Human Biology
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
The Blood Vessels
Blood vessels consist of arteries (and arterioles) that take blood away from the heart;
capillaries, in which trade of materials with the tissues takes place; and veins (and venules) that
take blood to the heart.
The Heart
The heart has a right and left side and four chambers. On the right side, an atrium gets O2-
negative blood from the body, and a ventricle pumps it into the pulmonary circuit. On the left
side, an atrium receives O2-rich blood from the lungs, and a ventricle pumps it into the systemic
circuit. During the cardiac cycle, the SA node (pacemaker) initiates the heartbeat by causing the
atria to contract. The AV node conveys the stimulus to the ventricles, causing them to contract.
The heart sounds, “lub-dup,” are caused by the closing of the atrioventricular valves, followed by
the closing of the semilunar valves.
Functions of the Cardiovascular System
The heart rate indicates the heartbeat rate. Blood pressure induced by the beating of the heart
accounts for the flow of blood in the arteries, but because blood pressure drops off after the
capillaries, it cannot cause blood flow in the veins. Skeletal muscle contraction, the presence of
valves, and respiratory movements account for blood flow in veins. The reduced speed of blood
flow in capillaries helps exchange of nutrients and wastes.
The Vascular Pathways
The cardiovascular system is divided into the pulmonary circuit and the systemic circuit. In
the pulmonary circuit, the pulmonary trunk from the right ventricle and the two pulmonary
arteries take O2-negative blood to the lungs, and four pulmonary veins return O2-rich blood to
the left atrium. To trace the path of blood in the systemic circuit, start with the aorta from the left
ventricle. Follow its path until it branches to an artery going to a specific organ. It can be
assumed that the artery divides into arterioles and capillaries, and that the capillaries lead to
venules. The vein that takes blood to the vena cava most likely has the same name as the artery
that delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the
arteries carry O2-rich blood, and the veins carry O2-poor blood.
Cardiovascular Disorders
Hypertension and atherosclerosis are two cardiovascular disorders that lead to stroke, heart
attack, and aneurysm. Medical and surgical methods are available to control cardiovascular
disease, but the best defense is prevention by following a heart-healthy diet, getting regular
exercise, maintaining a proper weight, and not smoking.
Homeostasis
Homeostasis is closely dependent on the cardiovascular system as it serves the needs of the
cells. However, several other body systems are crucial to the functioning of the cardiovascular
system. The digestive system supplies nutrients, and the respiratory system supplies oxygen and
removes carbon dioxide from the blood. Like the heart, the nervous and endocrine systems are
involved in maintaining the blood pressure that moves blood in the arteries and arterioles. The
lymphatic system returns tissue fluid to the veins where blood is propelled by skeletal muscle
contraction and respiratory movements.
Lymphatic System
The lymphatic system consists of lymphatic vessels and lymphoid organs. The lymphatic
vessels receive lipoproteins at intestinal villi and excess tissue fluid at blood capillaries and carry
these to the bloodstream. Lymphocytes are produced and accumulate in the lymphoid organs (red
bone marrow, lymph nodes, tonsils, spleen, and thymus gland). Lymph is cleansed of pathogens
and/or their toxins in lymph nodes, and blood is cleansed of pathogens and/or their toxins in the
spleen. T lymphocytes mature in the thymus, while B lymphocytes mature in the red bone
marrow where all blood cells are produced. White blood cells are necessary for nonspecific and
specific defenses.
Nonspecific Defenses
Immunity involves nonspecific and specific defenses. Nonspecific defenses include barriers to
entry, the inflammatory response, natural killer cells, and protective proteins.
Specific Defenses
Specific defenses require B lymphocytes and T lymphocytes, also known as B cells and T
cells. B cells undergo clonal selection with production of plasma cells and memory B cells after
their antigen receptors combine with a specific antigen. Plasma cells secrete antibodies and
eventually undergo apoptosis. Plasma cells are responsible for antibody-mediated immunity. IgG
antibody is a Y-shaped molecule that has two binding sites for a specific antigen. Memory B
cells remain in the body and produce antibodies if the same antigen enters the body at a later
date. T cells are responsible for cell-mediated immunity. The two major types of T cells are
cytotoxic T cells and helper T cells. Cytotoxic T cells kill virus-infected or cancer cells on
contact because they recognize a nonself antigen. Helper T cells produce cytokines and stimulate
other immune cells. Like B cells, each T cell bears antigen receptors. However, for a T cell to
recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), usually
a macrophage, along with an HLA (human leukocyte-associated antigen). Thereafter, the
activated T cell undergoes clonal expansion until the infection has been stemmed. Then most of
the activated T cells undergo apoptosis. Some cells remain, however, as memory T cells.
Induced Immunity
Immunity can be induced in various ways. Vaccines are available to induce long-lasting,
active immunity, and antibodies sometimes are available to provide an individual with
temporary, passive immunity. Cytokines, such as interferon, are used in an attempt to promote
the body’s ability to overcome cancer and to treat AIDS.
Immunity Side Effects
Allergic responses occur when the immune system reacts vigorously to substances not
normally recognized as foreign. Immediate allergic responses, usually involving coldlike
symptoms, are caused by the activity of antibodies. Delayed allergic responses, such as contact
dermatitis, are caused by the activity of T cells.
Respiratory Tract
The respiratory tract consists of the nose (nasal cavities), the nasopharynx, the pharynx, the
larynx (which includes the vocal cords), the trachea, the bronchi, the bronchioles, and the alveoli.
The bronchi, along with the pulmonary arteries and veins, enter the lungs, which include the
alveoli, air sacs surrounded by a capillary network.
Mechanism of Respiration
Inspiration begins when the respiratory center in the medulla oblongata sends excitatory nerve
impulses to the diaphragm and the muscles of the rib cage. As they contract, the diaphragm
lowers, and the rib cage moves upward and outward; the lungs expand, creating a partial
vacuum, which causes air to rush in. The respiratory center now stops sending impulses to the
diaphragm and muscles of the rib cage. As the diaphragm relaxes, it resumes its dome shape, and
as the rib cage retracts, air is pushed out of the lungs during expiration.
Gas Exchanges in the Body
External respiration occurs when CO2 leaves blood through the alveoli and O2 enters blood
from the alveoli. Oxygen is transported to the tissues in combination with hemoglobin as
oxyhemoglobin (HbO2). Internal respiration occurs when O2 leaves blood and CO2 enters blood
at the tissues. Carbon dioxide is primarily carried to the lungs in the plasma as the bicarbonate
ion (HCO3–). Hemoglobin combines with hydrogen ions and becomes reduced (HHb).
Respiration and Health
A number of diseases are associated with the respiratory tract. These disorders are divided into
those that affect the upper respiratory tract and those that affect the lower respiratory tract.
Infections of the nasal cavities, sinuses, throat, tonsils, and larynx are all well-known.
Additionally, infections can spread from the nasopharynx to the ears. The lower respiratory tract
is also subject to infections such as acute bronchitis, pneumonia, and pulmonary tuberculosis. In
restrictive pulmonary disorders, exemplified by pulmonary fibrosis, the lungs lose their
elasticity. In obstructive pulmonary disorders, exemplified by chronic bronchitis, emphysema,
and asthma, the bronchi (and bronchioles) do not efficiently conduct air to and from the lungs.
Smoking, which is associated with chronic bronchitis and emphysema, can eventually lead to
lung cancer.
Urinary System
The kidneys produce urine, which is carried by the ureters to the bladder where it is stored
before being released through the urethra. The kidneys excrete nitrogenous wastes, including
urea, uric acid, and creatinine. They maintain the normal water-salt balance and the acid-base
balance of the blood.
Kidneys
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis.
Microscopically, they contain the nephrons. Each nephron has its own blood supply; the afferent
arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary
tuft. The efferent arteriole leaves the capsule and immediately branches into the peritubular
capillary network. Each region of the nephron is anatomically suited to its task in urine
formation. The spaces between the podocytes of the glomerular capsule allow small molecules to
enter the capsule from the glomerulus. The cuboidal epithelial cells of the proximal convoluted
tubule have many mitochondria and microvilli to perform active transport (following passive
transport) from the tubule to the blood. In contrast, the cuboidal epithelial cells of the distal
convoluted tubule have numerous mitochondria but lack microvilli. They perform active
transport from the blood to the tubule.
Urine Formation
Urine is composed mainly of nitrogenous waste products and salts in water. The steps in urine
formation are glomerular filtration, tubular reabsorption, and tubular secretion
Maintaining Water-Salt Balance
The kidneys regulate the water-salt balance of the body. Water is reabsorbed from certain
parts of the tubule, and the loop of the nephron establishes an osmotic gradient that draws water
from the descending loop of the nephron and also from the collecting duct. The permeability of
the collecting duct is under the control of the hormone ADH. The reabsorption of salt increases
blood volume and pressure because more water is also reabsorbed. Other hormones, aldosterone
and ANH, control the kidneys’ reabsorption of sodium (Na+).
Maintaining Acid-Base Balance
The kidneys maintain blood pH within normal limits. They reabsorb HCO3– and excrete H+
as needed to maintain the pH at about 7.4.
Homeostasis
The urinary system works with the other systems of the body to maintain homeostasis in the
ways described in the illustration on page 198.
Problems with Kidney Function
Various types of problems, including recurrent urinary infections, can lead to renal failure,
which necessitates receiving a kidney from a donor or undergoing hemodialysis by applying a
kidney machine or CAPD.
