# BIOL 281: Human Physiology - Lecture Notes
## I. Introduction to Human Physiology & Homeostasis
### A. What is Physiology?
- The study of the function of the body's organ systems.
- Focuses on the mechanisms of how the body works, from the molecular level to the whole
organism.
### B. Levels of Structural Organization
1. **Chemical Level:** Atoms and molecules essential for life.
2. **Cellular Level:** The basic structural and functional units of an organism.
3. **Tissue Level:** Groups of similar cells that perform a specific function.
- Epithelial Tissue
- Connective Tissue
- Muscle Tissue
- Nervous Tissue
4. **Organ Level:** Structures composed of two or more different types of tissues with specific
functions.
5. **System Level:** Related organs with a common function.
6. **Organismal Level:** The entire living individual.
### C. Homeostasis: Maintaining a Stable Internal Environment
- **Definition:** The ability of the body to maintain relatively stable internal conditions despite
changes in the external environment.
- **Key Variables Maintained:**
- Temperature
- Blood glucose
- Blood pressure
- pH
- Oxygen and carbon dioxide levels
- **Feedback Systems:**
1. **Receptor:** Monitors changes in a controlled condition and sends input to a control
center.
2. **Control Center:** Sets the range of values, evaluates input, and generates output
commands.
3. **Effector:** Receives output from the control center and produces a response.
- **Types of Feedback Loops:**
- **Negative Feedback:** The response reverses the original stimulus. This is the most
common type of feedback loop in the body (e.g., regulation of body temperature, blood
pressure).
- **Positive Feedback:** The response enhances the original stimulus. This is less common
and is typically found in processes that need to be completed quickly (e.g., childbirth, blood
clotting).
## II. Cellular Physiology
### A. The Cell Membrane
- **Structure:** Phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.
- **Functions:**
- Physical isolation
- Regulation of exchange with the environment (selectively permeable)
- Sensitivity to the environment
- Structural support
### B. Transport Across the Cell Membrane
- **Passive Transport (No ATP required):**
- **Simple Diffusion:** Movement of a substance from an area of high concentration to low
concentration.
- **Facilitated Diffusion:** Movement of a substance down its concentration gradient with
the help of a membrane protein (carrier or channel).
- **Osmosis:** Movement of water across a selectively permeable membrane from an area
of high water concentration to low water concentration.
- **Active Transport (ATP required):**
- **Primary Active Transport:** Uses energy directly from ATP to transport substances against
their concentration gradient (e.g., Sodium-Potassium pump).
- **Secondary Active Transport:** Uses the energy stored in a concentration gradient of one
substance to drive the transport of another substance against its concentration gradient.
- **Vesicular Transport:**
- **Endocytosis:** Movement of substances into a cell in vesicles.
- **Phagocytosis:** "Cell eating"
- **Pinocytosis:** "Cell drinking"
- **Exocytosis:** Movement of substances out of a cell in vesicles.
## III. Neurophysiology
### A. Organization of the Nervous System
- **Central Nervous System (CNS):** Brain and spinal cord.
- **Peripheral Nervous System (PNS):** All nervous tissue outside the CNS.
- **Somatic Nervous System (SNS):** Voluntary control of skeletal muscles.
- **Autonomic Nervous System (ANS):** Involuntary control of smooth muscle, cardiac
muscle, and glands.
- **Sympathetic Division:** "Fight or flight"
- **Parasympathetic Division:** "Rest and digest"
### B. The Neuron
- **Dendrites:** Receive input.
- **Cell Body (Soma):** Contains the nucleus and organelles.
- **Axon:** Transmits electrical signals (action potentials).
- **Axon Terminals:** Release neurotransmitters.
### C. Membrane Potential
- **Resting Membrane Potential:** The electrical potential difference across the membrane of a
resting neuron (typically -70mV). Maintained by the Na+/K+ pump and leak channels.
- **Graded Potentials:** Small, localized changes in membrane potential that can be either
depolarizing or hyperpolarizing.
- **Action Potentials:** A rapid, all-or-none change in membrane potential used for long-
distance communication.
1. **Depolarization:** Voltage-gated Na+ channels open, Na+ rushes in.
2. **Repolarization:** Voltage-gated K+ channels open, K+ rushes out.
3. **Hyperpolarization:** K+ channels remain open, leading to a more negative membrane
potential than resting.
### D. The Synapse
- The junction between a neuron and another cell.
- **Chemical Synapse:**
1. Action potential arrives at the axon terminal.
2. Voltage-gated Ca2+ channels open, and Ca2+ enters the axon terminal.
3. Ca2+ influx causes synaptic vesicles to release neurotransmitters via exocytosis.
4. Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the
postsynaptic membrane.
5. Binding of neurotransmitter opens ion channels, creating a postsynaptic potential (either
excitatory or inhibitory).
## IV. The Endocrine System
### A. Principles of Endocrine Signaling
- **Hormones:** Chemical messengers released into the bloodstream that act on distant target
cells.
- **Endocrine Glands:** Ductless glands that secrete hormones (e.g., pituitary, thyroid, adrenal).
- **Target Cells:** Cells that have specific receptors for a particular hormone.
### B. Major Endocrine Glands and Their Hormones
- **Hypothalamus:** Controls the pituitary gland.
- **Pituitary Gland:**
- **Anterior Pituitary:** Growth Hormone (GH), Thyroid-Stimulating Hormone (TSH),
Adrenocorticotropic Hormone (ACTH), Follicle-Stimulating Hormone (FSH), Luteinizing Hormone
(LH), Prolactin (PRL).
- **Posterior Pituitary:** Stores and releases Antidiuretic Hormone (ADH) and Oxytocin.
- **Thyroid Gland:** Thyroxine (T4) and Triiodothyronine (T3) - regulate metabolism; Calcitonin -
lowers blood calcium.
- **Parathyroid Glands:** Parathyroid Hormone (PTH) - raises blood calcium.
- **Adrenal Glands:**
- **Adrenal Cortex:** Aldosterone (regulates salt and water balance), Cortisol (stress
response), Androgens.
- **Adrenal Medulla:** Epinephrine and Norepinephrine ("fight or flight").
- **Pancreas:** Insulin (lowers blood glucose), Glucagon (raises blood glucose).
- **Gonads:**
- **Ovaries:** Estrogen and Progesterone.
- **Testes:** Testosterone.
### C. Mechanisms of Hormone Action
- **Water-Soluble Hormones (e.g., peptides, catecholamines):** Bind to receptors on the cell
surface and act via second messengers.
- **Lipid-Soluble Hormones (e.g., steroids, thyroid hormones):** Diffuse through the cell
membrane and bind to intracellular receptors, directly altering gene expression.
## V. The Muscular System
### A. Types of Muscle Tissue
- **Skeletal Muscle:** Striated, voluntary, attached to bones.
- **Cardiac Muscle:** Striated, involuntary, found only in the heart.
- **Smooth Muscle:** Non-striated, involuntary, found in the walls of hollow organs.
### B. Skeletal Muscle Physiology
- **Sarcomere:** The basic functional unit of a myofibril. Composed of thick (myosin) and thin
(actin) filaments.
- **Sliding Filament Theory:** During muscle contraction, thin filaments slide past thick
filaments, causing the sarcomere to shorten.
- **Excitation-Contraction Coupling:**
1. An action potential in a motor neuron releases acetylcholine (ACh) at the neuromuscular
junction.
2. ACh binding to receptors on the muscle fiber membrane generates a muscle action
potential.
3. The action potential travels down the T-tubules, causing the sarcoplasmic reticulum to
release Ca2+.
4. Ca2+ binds to troponin, which moves tropomyosin away from the myosin-binding sites on
actin.
5. Myosin heads bind to actin and perform a power stroke, pulling the thin filaments toward
the center of the sarcomere.
- **Motor Unit:** A single motor neuron and all the muscle fibers it innervates.
## VI. The Cardiovascular System
### A. Components of the Cardiovascular System
- **Heart:** A four-chambered pump.
- **Blood Vessels:** Arteries, arterioles, capillaries, venules, and veins.
- **Blood:** A fluid connective tissue.
### B. The Heart
- **Chambers:** Right Atrium, Right Ventricle, Left Atrium, Left Ventricle.
- **Valves:** Ensure one-way blood flow (Tricuspid, Pulmonary, Mitral/Bicuspid, Aortic).
- **Blood Flow through the Heart:**
- Deoxygenated blood enters the right atrium -> right ventricle -> pulmonary artery -> lungs.
- Oxygenated blood from the lungs enters the left atrium -> left ventricle -> aorta -> rest of the
body.
- **Cardiac Conduction System:**
1. Sinoatrial (SA) node (pacemaker)
2. Atrioventricular (AV) node
3. Bundle of His
4. Right and Left Bundle Branches
5. Purkinje fibers
### C. The Cardiac Cycle
- **Systole:** Contraction phase of the ventricles.
- **Diastole:** Relaxation phase of the ventricles.
- **Electrocardiogram (ECG or EKG):** A recording of the electrical activity of the heart.
- **P wave:** Atrial depolarization.
- **QRS complex:** Ventricular depolarization.
- **T wave:** Ventricular repolarization.
### D. Blood Vessels and Blood Pressure
- **Arteries:** Carry blood away from the heart.
- **Veins:** Carry blood toward the heart.
- **Capillaries:** The site of exchange between blood and tissues.
- **Blood Pressure:** The force exerted by blood on the walls of blood vessels.
- **Systolic Pressure:** The highest pressure in arteries during ventricular systole.
- **Diastolic Pressure:** The lowest pressure in arteries during ventricular diastole.
## VII. The Respiratory System
### A. Functions of the Respiratory System
- Gas exchange (O2 and CO2).
- Regulation of blood pH.
- Vocalization.
### B. Anatomy of the Respiratory System
- **Upper Respiratory Tract:** Nose, pharynx, and associated structures.
- **Lower Respiratory Tract:** Larynx, trachea, bronchi, and lungs.
- **Alveoli:** Tiny air sacs in the lungs where gas exchange occurs.
### C. Pulmonary Ventilation (Breathing)
- **Inspiration (Inhalation):** An active process involving the contraction of the diaphragm and
external intercostal muscles, which increases the volume of the thoracic cavity and decreases
intrapulmonary pressure.
- **Expiration (Exhalation):** A largely passive process at rest, involving the relaxation of the
inspiratory muscles, which decreases the volume of the thoracic cavity and increases
intrapulmonary pressure.
### D. Gas Exchange
- **External Respiration:** Exchange of gases between the alveoli and the blood in the
pulmonary capillaries.
- **Internal Respiration:** Exchange of gases between the blood in systemic capillaries and
tissue cells.
- **Gas transport in the blood:**
- **Oxygen:** Primarily transported bound to hemoglobin in red blood cells.
- **Carbon Dioxide:** Transported in three ways:
1. Dissolved in plasma.
2. Bound to hemoglobin.
3. As bicarbonate ions (HCO3-) in the plasma.
## VIII. The Renal System
### A. Functions of the Kidneys
- Regulation of blood volume and composition.
- Regulation of blood pressure.
- Production of hormones (calcitriol and erythropoietin).
- Excretion of wastes.
### B. The Nephron: The Functional Unit of the Kidney
- **Renal Corpuscle:**
- **Glomerulus:** A capillary network.
- **Bowman's Capsule:** Surrounds the glomerulus.
- **Renal Tubule:**
- Proximal Convoluted Tubule (PCT)
- Loop of Henle
- Distal Convoluted Tubule (DCT)
### C. Urine Formation
1. **Glomerular Filtration:** Water and most solutes in blood plasma move across the
glomerular capillaries into Bowman's capsule.
2. **Tubular Reabsorption:** The process of returning needed substances from the filtrate back
to the blood.
3. **Tubular Secretion:** The process of moving substances from the blood into the filtrate.
### D. Regulation of Kidney Function
- **Hormonal Control:**
- **Antidiuretic Hormone (ADH):** Increases water reabsorption.
- **Aldosterone:** Increases Na+ reabsorption and K+ secretion.
- **Atrial Natriuretic Peptide (ANP):** Decreases Na+ and water reabsorption.
## IX. The Digestive System
### A. Functions of the Digestive System
1. **Ingestion:** Taking in food.
2. **Secretion:** Release of water, acid, buffers, and enzymes.
3. **Motility:** Mixing and moving of food and secretions.
4. **Digestion:** Breakdown of food into smaller molecules.
- **Mechanical Digestion:** Chewing, churning.
- **Chemical Digestion:** Enzymatic breakdown.
5. **Absorption:** Passage of digested products into the blood or lymph.
6. **Defecation:** Elimination of feces.
### B. Phases of Digestion
1. **Cephalic Phase:** The smell, sight, thought, or initial taste of food activates neural centers
and prepares the mouth and stomach for food to be eaten.
2. **Gastric Phase:** Begins when food reaches the stomach.
3. **Intestinal Phase:** Begins when food enters the small intestine.
### C. Major Organs of the Digestive Tract
- **Mouth:** Mechanical digestion (chewing) and chemical digestion of carbohydrates.
- **Stomach:** Secretes gastric juice (HCl and pepsin) for protein digestion.
- **Small Intestine:** The primary site of digestion and absorption of nutrients.
- **Large Intestine:** Absorption of water and electrolytes, and formation of feces.
### D. Accessory Digestive Organs
- **Liver:** Produces bile, which emulsifies fats.
- **Gallbladder:** Stores and concentrates bile.
- **Pancreas:** Produces pancreatic juice containing digestive enzymes and bicarbonate.
## X. The Reproductive System
### A. Male Reproductive System
- **Testes:** Produce sperm and testosterone.
- **Duct System (epididymis, ductus deferens, ejaculatory duct, urethra):** Transports and stores
sperm.
- **Accessory Glands (seminal vesicles, prostate, bulbourethral glands):** Secrete seminal fluid.
### B. Female Reproductive System
- **Ovaries:** Produce oocytes (eggs) and hormones (estrogen and progesterone).
- **Uterine (Fallopian) Tubes:** Site of fertilization.
- **Uterus:** Site of implantation of a fertilized ovum and development of the fetus.
- **Vagina:** Receives the penis during sexual intercourse and serves as a passageway for
childbirth.
### C. The Ovarian and Uterine Cycles
- **Ovarian Cycle:** A series of events in the ovaries that occur during and after the maturation
of an oocyte.
- **Follicular Phase:** Development of the ovarian follicle.
- **Ovulation:** Release of the oocyte from the ovary.
- **Luteal Phase:** Formation of the corpus luteum.
- **Uterine (Menstrual) Cycle:** A concurrent series of changes in the endometrium of the
uterus to prepare for the arrival of a fertilized ovum.
- **Menstrual Phase:** Shedding of the endometrium.
- **Proliferative Phase:** Rebuilding of the endometrium.
- **Secretory Phase:** Endometrium prepares for implantation.
