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HUMAN BIOLOGY Seventeenth Edition

Sylvia S. Mader Michael Windelspecht

Chapter 9 Digestive System

and Nutrition

9.1 Overview of Digestion 1

Learning Outcomes: • State the function of each organ of the

gastrointestinal tract. • List the accessory organs and name a function for

each. • Describe the structure of the gastrointestinal tract

wall.

9.1 Overview of Digestion 2

Overview of the digestive system. The organs are located within the gastrointestinal (GI) tract.

Function—to hydrolyze, or break down, the macromolecules found in food. • The subunit molecules (monosaccharides, amino acids,

fatty acids, and glycerol) can cross plasma membranes using facilitated and active transport.

The nutrients made available are transported by the blood to our cells.

Organs of the GI Tract and Accessory Structures of Digestion (Figure 9.1)

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Processes of Digestion

Digestion processes: Ingestion—intake of food via the mouth.

Digestion—mechanically or chemically breaking down foods into their subunits. • Mechanical digestion—chewing in the mouth and

contractions of smooth muscles in the stomach.

• Chemical digestion—digestive enzymes hydrolyze macromolecules into subunits.

• Begins in the mouth, continues in the stomach, and is completed in the small intestine.

Stages of Digestion

Digestion processes, continued.

Movement—food is passed from one organ to the next, normally by contractions of smooth muscle called peristalsis; indigestible must be expelled.

Absorption—movement of nutrients across the GI tract wall into the blood; they are then delivered to cells.

Elimination—removal of indigestible wastes. • Defecation.

Wall of the Digestive Tract 1

Wall of the digestive tract. Lumen—open area of a hollow organ or vessel; in the GI tract, it contains food or feces.

Layers: • Mucosa—innermost layer; produces mucus for protection; also

produces digestive enzymes.

• Submucosa—loose connective tissue; contains blood vessels, lymphatic vessels, and nerves.

• Muscularis—made of two layers of smooth muscle (inner, circular layer, and an outer, longitudinal layer) that move food along the GI tract.

• Serosa—outer lining; is part of the peritoneum.

The Layers of the Gastrointestinal Tract Wall (Figure 9.2)

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Wall of the Digestive Tract 2

Diverticulosis. A condition in which the mucosa of any part of the GI tract (usually the large intestine) pushes through the other layers and forms pouches where food collects.

Diverticulitis—when the pouches become infected. • This happens in 10–25% of people with diverticulosis.

Bowel Disease

Inflammatory bowel disease (IBD)—chronic diarrhea, abdominal pain, fever, and weight loss. Irritable bowel syndrome (IBS)—contractions of the muscularis cause abdominal pain, constipation, and diarrhea. • The underlying cause is not known.

Check Your Progress 9.1

List the digestive organs and accessory structures of the digestive system.

Describe the processes that occur during the digestive process.

Identify the four layers of the GI tract from the lumen outward.

9.2 The Mouth, Pharynx, and Esophagus

Learning Outcomes: • Identify the structures of the mouth, pharynx, and

esophagus and provide a function for each. • Explain the series of events involved in swallowing. • Summarize the diseases and conditions associated

with the mouth, pharynx, and esophagus.

The Mouth 1

Mouth (oral cavity). Receives food and begins mechanical and chemical digestion.

The roof of the mouth separates the nasal cavity from the oral cavity. • Two parts: a bony hard palate and a soft palate.

• The soft palate is made of muscle; ends in the uvula.

Tonsils—in the back of the mouth on either side of the tongue. • Lymphatic tissue; help protect from disease.

• There is a single pharyngeal tonsil in the nasopharynx, commonly called the adenoids.

Structures of the Mouth (Figure 9.3a) 1

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The Mouth 2

Mouth (oral cavity), continued. Three pairs of salivary glands secrete saliva, which contains: • Salivary amylase—begins carbohydrate digestion.

• Lysozyme—antibacterial enzyme.

Tongue. • Covered in taste buds.

• Assists in mechanical breakdown, movement of food.

• Forms a bolus (mass of chewed food) and moves it toward the pharynx.

The Mouth 3

Teeth. Mechanically digest food.

20 smaller deciduous (baby) teeth, 32 adult teeth.

Two main divisions: • Crown—the part of the tooth above the gum line.

• Root—the portion below.

The Mouth 4

Teeth, continued. • Enamel—extremely hard outer layer. • Dentin—a thick layer of bonelike material. • Pulp—nerves and blood vessels. • Periodontal membranes—anchor the tooth to the

jawbone.

Structures of the Mouth (Figure 9.3b) 2

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The Mouth 5

Teeth, continued. Dental caries—tooth decay, cavities. • Occur when bacteria metabolize sugar and produce acids,

which erode the teeth.

• Can be painful when it reaches the nerves of the pulp.

Gingivitis—inflammation of the gums; can spread to the periodontal membrane, causing loosening of the teeth.

Periodontitis—loss of bone and loosening of the teeth.

The Pharynx and Esophagus

The mouth and nasal passages lead to the pharynx. In turn, the pharynx opens into both the food passage (esophagus) and air passage (trachea, or windpipe). • These two tubes are parallel to each other; the trachea is

in front of the esophagus.

• The esophagus is a muscular tube that leads to the stomach.

Swallowing

Swallowing. Starts off voluntary, but once food or drink is pushed back into the pharynx, it becomes an involuntary reflex.

Food normally enters the esophagus because other possible avenues are blocked. • The soft palate moves back to close off the nasal passage,

and the trachea moves up under the epiglottis to cover the glottis, the opening to the larynx.

The Process of Swallowing (Figure 9.4)

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Peristalsis 1

Peristalsis—contractions that push food through the digestive tract. Sphincter—a ring of muscle that acts as a valve. When it contracts, it stops food from moving through; when it relaxes, it allows food through.

That is, the lower esophageal sphincter is between the esophagus and the stomach. • Heartburn—failure of this sphincter; stomach contents move

from the stomach into the esophagus.

Peristalsis 2

Vomiting—when strong contractions of the abdominal muscles and the diaphragm (the muscle separating the thoracic and abdominal cavities) force the contents of the stomach into the esophagus and oral cavity.

Check Your Progress 9.2

Describe the role of the mouth, pharynx, and esophagus in digestion. Detail how mechanical digestion and chemical digestion occur in the mouth. Explain what ordinarily prevents food from entering the nose or trachea when you swallow.

9.3 The Stomach and Small Intestine

Learning Outcomes: • Describe the structure of the stomach and explain

its role in digestion. • Describe the structure of the small intestine and

explain its role in digestion. • Explain how carbohydrates, lipids, and proteins are

processed by the small intestine.

The Stomach 1

Stomach. Stores food, starts digestion of proteins, and controls movement of food into the small intestine.

Does not absorb nutrients. • However, it does absorb alcohol, because alcohol is fat-

soluble and can pass through membranes easily.

There are three layers of muscle in the muscularis layer (instead of two) to help in mechanical digestion. • Circular, longitudinal, and third oblique layer.

Structure of the Stomach (Figure 9.5)

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(c): Steve Gschmeissner/Brand X Pictures/SPL/Getty Images 28

The Stomach 2

Heartburn (GERD). • The lining of the esophagus is thinner than the lining

of the stomach; if chyme enters the esophagus, it produces a burning sensation.

• Can be caused by pregnancy and excess fat pushing on the stomach.

• Gastroesophageal reflux disease (GERD)—chronic heartburn.

The Stomach 3

Stomach, continued. The mucosa has deep folds called rugae.

The mucosa also has gastric pits, which contain gastric glands. • The gastric glands produce gastric juice, which contains:

• Pepsin—digests proteins.

• Hydrochloric acid (HCl)—pH of 2.

• Kills bacteria and activates pepsin.

• Mucus.

The Stomach 4

Stomach, continued. Normally, the stomach empties in 2–6 hours.

Chyme—a mixture of food and gastric juice. • Pyloric sphincter—allows only a small amount of chyme

to enter the small intestine at a time.

The Small Intestine 1

The small intestine—named for its small diameter compared with the large intestine’s. The small intestine is very long, longer than the large intestine. • Averaging about 6 m (18 ft) in length, whereas the large

intestine is about 1.5 m (4.5 ft).

It consists of three regions: • Duodenum.

• Jejunum.

• Ileum. 32

The Small Intestine 2

The Small Intestine Is the Main Digestive Organ. Pancreas—secretes digestive enzymes through a duct into the duodenum, the first portion of the small intestine.

Another duct brings bile from the liver and gallbladder into the duodenum.

Bile emulsifies fat. • Mechanical digestion; causes fat droplets to disperse in water to

expose more of it to lipase.

• Produced by the pancreas, it hydrolyzes fats into glycerol and fatty acids.

The Small Intestine 3

The Small Intestine Is the Main Digestive Organ, continued. Pancreatic amylase—produced by the pancreas, secreted into the duodenum. • Digests carbohydrates.

Trypsin—produced by the pancreas, secreted into the duodenum. • Digests proteins, so is a protease—a class of enzymes that digest

proteins.

Pancreatic juice contains sodium bicarbonate, which neutralizes acidic chime.

Major Digestive Enzymes (Table 9.1) 1

Table 9.1a Major Digestive Enzymes: Carbohydrate Digestion Enzyme Produced By Site of Action Optimum pH Function

Salivary amylase Salivary glands Mouth Neutral Begins the breakdown of starch to maltose

Pancreatic amylase Pancreas Small intestine Basic Breakdown of starch to maltose Maltase Small intestine Small intestine Basic Breakdown of maltose to glucose Lactase Small intestine Small intestine Basic Breakdown of lactose to glucose

and galactose

Table 9.1b Major Digestive Enzymes: Protein Digestion Enzyme Produced By Site of Action Optimum pH Function

Pepsin Gastric glands Stomach Acidic Breakdown of proteins to peptides and amino acids

Trypsin Pancreas Small intestine Basic Breakdown of proteins to peptides and amino acids

Peptidases Small intestine Small intestine Basic Breakdown of peptides to amino acids

Major Digestive Enzymes (Table 9.1) 2

Table 9.1c Major Digestive Enzymes: Nucleic Acid Digestion Enzyme Produced By Site of Action Optimum pH Function

Nuclease Pancreas Small intestine Basic Breakdown of nucleic acids to nucleotides

Nucleosidases Small intestine Small intestine Basic Breakdown of nucleotides to phosphates, bases, and sugars

Table 9.1d Major Digestive Enzymes: Fat Digestion Enzyme Produced By Site of Action Optimum pH Function

Salivary lipase

Salivary glands Mouth Neutral Begins the breakdown of triglycerides into fatty acids

Lipase Pancreas Small intestine Basic Breakdown of lipids to glycerol and fatty acids

The Small Intestine 4

Nutrients Are Absorbed in the Small Intestine. The mucosa contains fingerlike projections called villi (sing., villus). The cells that cover the villi have microvilli. • Give the villi a fuzzy “brush border.”

• Contain brush border enzymes that complete digestion.

These two structures greatly increase the surface area of the small intestine for absorption of nutrients.

Absorption in the Small Intestine (Figure 9.6)

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(photos) (b): Al Telser/McGraw Hill; (c): Steve Gschmeissner/Science Photo Library/Getty Images 38

The Small Intestine 5

Nutrients Are Absorbed in the Small Intestine, continued. Nutrients are absorbed into the villi, which contain blood capillaries and a small lymphatic capillary called a lacteal. • Monosaccharides and amino acids enter the blood capillaries of a

villus.

• Glycerol and fatty acids form lipoprotein droplets called chylomicrons, which then enter a lacteal.

After nutrients are absorbed, they are eventually carried to all the cells of the body by the blood.

Digestion and Absorption of Organic Nutrients (Figure 9.7)

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Lactose Intolerance

Lactose Intolerance. Lactose is the primary sugar in milk.

Lactase—the brush border enzyme that digests lactose.

Characterized by diarrhea, gas, bloating, and abdominal cramps after ingesting milk and other dairy products. • Diarrhea occurs because the undigested lactose causes fluid retention

in the small intestine.

• Gas, bloating, and cramps occur when bacteria break down the lactose anaerobically.

Celiac Disease

Celiac Disease. • Autoimmune response against a protein called

gluten, which is naturally found in grains such as wheat, barley, and rye.

• The presence of gluten in the small intestine results in an inflammatory response, which damages the villi and microvilli of the small intestine.

• Can lead to abdominal pain, diarrhea, and malnutrition.

Check Your Progress 9.3

Describe the functions of the stomach and how the wall of the stomach is modified to perform these functions. Detail the functions of the small intestine and how the wall of the small intestine is modified to perform these functions. Summarize the differences in how carbohydrates, proteins, and fats are digested and absorbed by the small intestine.

9.4 The Accessory Organs and Regulation of Secretions

Learning Outcomes: • Explain the functions of the pancreas, liver, and

gallbladder during digestion. • List the secretions of the pancreas, liver, and

gallbladder. • Summarize how secretions of the accessory organs

are regulated.

The Accessory Organs 1

Pancreas.

Located behind the stomach.

Most pancreatic cells produce pancreatic juice, which enters the duodenum via the pancreatic duct. • Contains sodium bicarbonate and digestive enzymes.

Accessory Organs of the Digestive System (Figure 9.8)

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The Accessory Organs 2

Pancreas, continued. Also an endocrine gland; secretes the hormone insulin when the blood glucose levels rise.

Type 1 diabetes—not enough insulin. • Normally diagnosed in childhood.

Type 2 diabetes—the body’s cells are insulin- resistant. • Normally occurs in adulthood.

• Risk factors: obesity, inactivity, family history.

The Accessory Organs 3

Liver. The largest gland in the body.

Lies mainly in the upper right abdominal cavity, under the diaphragm.

Lobules—structural and functional units.

The hepatic portal vein brings blood to the liver from the GI tract. • The lobules filter this blood, removing poisonous

substances.

Functions of the Liver (Table 9.2)

Table 9.2 Functions of the Liver 1. Destroys old red blood cells; excretes bilirubin, a breakdown product of

hemoglobin in bile, a liver product 2. Detoxifies blood by removing and metabolizing poisonous substances 3. Stores iron (Fe raised to the 2 plus power), the water-soluble vitamin B12, and the fat-soluble

vitamins A, D, E, and K 4. Makes plasma proteins, such as albumins and fibrinogen, from amino

acids 5. Stores glucose as glycogen after a meal; breaks down glycogen to glucose

to maintain the glucose concentration of blood between eating periods 6. Produces urea after breaking down amino acids 7. Helps regulate blood cholesterol level, converting some to bile salts

The Accessory Organs 4

Liver, continued. Stores vitamins.

Involved in blood glucose homeostasis. • Stores glucose as glycogen; when blood glucose is low, it

releases glucose by breaking down glycogen.

• Converts glycerol and amino acids to glucose.

• As amino acids are converted to glucose, urea is formed.

Produces plasma proteins.

Regulates blood cholesterol levels.

The Accessory Organs 5

Liver, concluded. Produces bile, which contains bile salts, water, cholesterol, and bicarbonate. • Contains bilirubin, a green pigment formed from the

breakdown of hemoglobin.

The Accessory Organs 6

Gallbladder. • Pear-shaped organ just below the liver. • Stores bile. • Gallstones—made of a stone-like material.

Liver Disorders

Liver disorders: hepatitis and cirrhosis. Liver disease can cause bile pigments to leak into the blood, causing jaundice. • Yellowish tint to the whites of the eyes and the skin.

Hepatitis. • Inflammation of the liver.

• Has different forms.

Hepatitis

Hepatitis, continued. Hepatitis A—usually acquired from sewage- contaminated drinking water and food.

Hepatitis B—usually from sexual contact, but also from blood transfusions or contaminated needles. • More contagious than the AIDS virus and is spread in the

same way.

• Vaccines are available for hepatitis A and B.

Hepatitis C—usually acquired by infected blood. • Can lead to chronic hepatitis, liver cancer, and death.

Cirrhosis

Cirrhosis. Chronic disease; first, liver becomes fatty, and then filled with fibrous scar tissue.

Often seen in people with obesity and alcohol use disorder, due to malnutrition and the excessive alcohol (a toxin) the liver is forced to break down.

The liver can regenerate and recover if the rate of regeneration exceeds the rate of damage. • During liver failure there may not be enough time to let

the liver heal so will need a liver transplantation.

Regulation of Digestive Secretions 1

Secretion of digestive juices is controlled by the nervous system and digestive hormones. When you look at or smell food, the parasympathetic nervous system stimulates gastric secretion.

A meal rich in protein causes the stomach to produce the hormone gastrin. • Increases the secretory activity of gastric glands.

Hormonal Control and Regulation of Digestion (Figure 9.9)

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Regulation of Digestive Secretions 2

Nervous system and hormonal control, continued. Secretin—secreted by the duodenum. • Release is stimulated by HCl (present in chyme).

Cholecystokinin (CCK)—released by the duodenum when proteins and fat are present. • Causes the liver to increase production of bile and causes

the gallbladder to contract and release stored bile.

• These hormones increase the production of pancreatic juice.

Check Your Progress 9.4

Name and describe the functions of three main accessory organs that assist with the digestive process.

Discuss what could occur if each of the accessory organs of digestion did not function properly.

Detail why the regulation of digestive secretions is important to the overall process of digestion. Describe what could occur without regulation.

9.5 The Large Intestine and Defecation

Learning Outcomes: • Describe the structure and function of the large

intestine. • List the disorders of the large intestine and provide a

cause for each.

The Large Intestine 1

Large intestine—includes the cecum, the colon, the rectum, and the anal canal. Larger in diameter than the small intestine, but it is shorter in length.

Cecum—the first portion. • Vermiform appendix—projection off of the cecum.

• Fights infections.

• Appendicitis—inflamed appendix; can cause peritonitis, a life-threatening infection of the peritoneum.

The Regions of the Large Intestine (Figure 9.10)

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The Large Intestine 2

Large intestine, continued. Colon—includes the ascending colon, which goes up the right side of the body; transverse colon, which crosses the abdominal cavity; descending colon, which passes down the left side; and the sigmoid colon, which enters the rectum, the last portion of the large intestine. • The rectum opens at the anus, where defecation, the

expulsion of feces, occurs.

Functions of the Large Intestine 1

Functions of the large intestine. Does not produce digestive enzymes.

Does not absorb nutrients except certain vitamins.

Absorbs water from feces to prevent dehydration.

Absorbs vitamins produced by intestinal flora, the bacteria that inhabit the intestine. • Bacteria break down indigestible material and produce B-

complex vitamins and vitamin K.

Functions of the Large Intestine 2

Functions of the large intestine, continued. Forms feces. • ¾ water, ¼ solid wastes.

• Bacteria and dietary fiber (indigestible remains) make up the solid wastes.

• Bacteria digesting the indigestible materials causes the odor of feces and accounts for the gas.

• Stercobilin, a breakdown product of bilirubin, and oxidized iron cause the brown color of feces.

Functions of the Large Intestine 3

Functions of the large intestine, concluded. Defecation—ridding the body of feces. • Peristalsis forces feces into the rectum.

• Stretching of the rectal wall initiates nerve impulses to the spinal cord.

• Then the rectal muscles contract and the anal sphincters relax, allowing the feces to exit the body through the anus.

• Can inhibit defecation by contracting the external anal sphincter, which is made of skeletal muscle.

Disorders of the Colon and Rectum 1

Diarrhea—increased peristalsis and failure to absorb water from feces, due to either an infection or nervous stimulation.

Constipation—dry, hard feces; may be controlled with water and fiber.

Hemorrhoids—enlarged, inflamed blood vessels of the anus due to chronic constipation, pregnancy, aging, anal intercourse.

Diverticulosis—pouches; weak spots in the muscularis layer.

Disorders of the Colon and Rectum 2

Irritable bowel syndrome (IBS), or spastic. colon—the muscularis contracts powerfully but without normal coordination. • Symptoms: abdominal cramps, gas, constipation, and

urgent, explosive stools.

Disorders of the Colon and Rectum 3

Inflammatory bowel disease (IBD)—includes: Ulcerative colitis—affects the large intestine and rectum. • Results in diarrhea, rectal bleeding, abdominal cramps, and urgency to

defecate.

Crohn’s disease—usually in the small intestine. • Ulcers in the intestinal wall; they are painful and bleed as they erode

the submucosal layer, where there are nerves and blood vessels.

• Can’t absorb nutrients in the affected areas.

• Symptoms: diarrhea, weight loss, abdominal cramping, anemia, bleeding, and malnutrition.

Disorders of the Colon and Rectum 4

Polyps and cancer. Polyps—small growths in the colon lining. • Can be benign or cancerous.

• If colon cancer is detected while still confined to a polyp, the expected outcome is a complete cure.

• Increased dietary fat raises the risk of colon cancer.

• Fiber in the diet inhibits colon cancer, and regular elimination reduces the time that the colon wall is exposed to cancer-promoting agents in the feces.

Check Your Progress 9.5

Describe the parts of the large intestine, and provide the function for each. Explain the role of the large intestine in the digestive tract. Describe how constipation and diarrhea are related to the large intestine.

9.6 Nutrition and Weight Control 1

Learning Outcomes: • Calculate a BMI value and interpret its relationship

to your overall health. • Identify the role of each class of nutrient in the

human body.

9.6 Nutrition and Weight Control 2

Obesity—significantly overweight. One of the greatest health problems in the United States. • Almost 42% of adults and 18.5% of children are obese.

• Excess body fat is associated with a higher risk for premature death, type 2 diabetes, hypertension, cardiovascular disease, stroke, osteoarthritis, and certain types of cancer.

Defining Obesity

Defining obesity. Having a body mass index (BMI) of 30 or greater. • Weight in kilograms (kg) is divided by the height in 2m .

2m .

BMI Values (Table 9.3)

Table 9.3 BMI Values Classification BMI Values Healthy 18.5 to 24.9 Overweight 25.0 to 29.9 Obese 30.0 to 39.9 Extremely (morbid) obese 40.0 and higher

The Body Mass Index Chart (Figure 9.11)

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Source: Adapted from "Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report." 76

Classes of Nutrients

Classes of nutrients. Nutrient—a required component of food that performs a physiological function in the body. • Provides energy, promotes growth and development, and

regulates cellular metabolism.

• Includes carbohydrates, proteins, lipids, minerals, and vitamins.

Carbohydrates 1

Carbohydrates—are either simple or complex. Glucose—simple sugar.

Complex carbohydrates are digested to glucose.

Although body cells can use fatty acids as an energy source, brain cells require glucose.

Any product made from refined grains, such as white bread, cake, and cookies, should be minimized in the diet. • During refinement of grains, fiber is removed, along with

vitamins and minerals. 78

Carbohydrates 2

Carbohydrates, continued. • Sources of complex carbohydrates, such as beans,

peas, nuts, fruits, and whole-grain products, are good sources of vitamins, minerals, and fiber.

• Insoluble fiber adds bulk to the feces and stimulates movements of the large intestine, preventing constipation.

• Soluble fiber combines with bile salts and cholesterol in the small intestine and prevents them from being absorbed.

Carbohydrates 3

Can carbohydrates be harmful? High intake of refined carbohydrates and fructose sweeteners contribute to obesity. In addition, they have a high glycemic index, because they quickly increase blood glucose. • When blood glucose levels rise rapidly, the pancreas

produces a lot of insulin to bring the level down.

• Chronically high insulin levels may lead to insulin resistance, type 2 diabetes, and increased fat deposition.

Reducing High-Glycemic-Index Carbohydrates (Table 9.4)

Table 9.4 Reducing High-Glycemic-Index Carbohydrates To Reduce Dietary Sugar

• Eat fewer sweets, such as candy, soft drinks, ice cream, and pastries. • Eat fresh or frozen fruits or fruits canned without heavy syrup. Avoid

artificial fruit juices. • Use less sugar—white, brown, or raw—and less honey and syrups. • Avoid sweetened breakfast cereals. • Eat less jelly, jam, and preserves. • When cooking, use spices, such as cinnamon, instead of sugar to flavor

foods. • Do not put sugar in tea or coffee. • Avoid processed foods made from refined carbohydrates, such as white

bread, rice, and pasta, and limit potato intake.

Proteins 1

Proteins—made of 20 different amino acids. There are eight essential amino acids—must be attained through the diet.

Complete proteins—contain all essential amino acids; usually derived from animal sources. • Non-animal sources of complete proteins are tofu, soymilk, and other

processed food from soybeans.

Incomplete proteins—plant sources; need to combine them to get all essential amino acids. • Must ingest essential amino acids every day; they are not stored in

the body.

Proteins 2

Can proteins be harmful? An overabundance of protein intake can result in dehydration during exercise. • Can also lead to calcium loss in urine, which can lead to

kidney stones.

Eating red meat can lead to cardiovascular disease since it is high in saturated fats.

Lipids 1

Lipids—include fats, oils, and cholesterol. Saturated fats. • Usually of animal origin.

• Solid at room temperature (unsaturated fats are usually liquid at room temperature).

• That is, butter, fat in meat, coconut oil, and palm oil.

Unsaturated fats. • Don’t promote cardiovascular disease.

• That is, corn oil and safflower oil are high in polyunsaturated fatty acids.

Lipids 2

Lipids, continued. Polyunsaturated oils contain the essential fatty acids linoleic acid and linolenic acid.

Olive oil and canola oil have more monounsaturated fatty acids than others.

Omega-3 fatty acids preserve brain function and protect against heart disease. • Flaxseed, cold-water fish are excellent sources.

Saturated and Unsaturated Fatty Acids (Figure 9.14)

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Lipids 3

Can lipids be harmful?

The risk for cardiovascular disease is increased by a diet high in saturated fats and cholesterol. • Saturated fats contribute to the formation of

atherosclerotic plaques that limit blood flow. • Cholesterol is carried in the blood by two transport

proteins: high-density lipoprotein (HDL) and low-density lipoprotein (LDL). • HDL (the “good” lipoprotein) ends up in the liver, where the

cholesterol is metabolized. • LDL (the “bad” lipoprotein) ends up being deposited in the

tissues.

Lipids 4

Can lipids be harmful? continued. Trans fatty acids (trans fats) arise when unsaturated fatty acids are hydrogenated to produce a solid fat. • Found in commercially packaged goods, such as cookies

and crackers. • If something contains partially hydrogenated vegetable oil, it

contains trans fats.

Reducing Lipids in the Diet (Table 9.5) 1

Table 9.5a Reducing Lipids in the Diet To Reduce Saturated Fats and Trans Fats in the Diet

• Choose poultry, fish, or dry beans and peas as a protein source. • Remove skin from poultry, and trim fat from red meats before cooking;

place on a rack, so that fat drains off. • Broil, boil, or bake rather than fry. • Limit your intake of butter, cream, trans fats, shortenings, and tropical

oils (coconut and palm oils). • Use herbs and spices to season vegetables instead of butter, margarine,

or sauces. Use lemon juice instead of salad dressing. • Drink skim milk instead of whole milk and use skim milk in cooking and

baking.

Reducing Lipids in the Diet (Table 9.5) 2

Table 9.5b Reducing Lipids in the Diet To Reduce Dietary Cholesterol

• Avoid cheese, egg yolks, liver, and certain shellfish (shrimp and lobster). Preferably, eat white fish and poultry.

• Substitute egg whites for egg yolks in both cooking and eating. • Include soluble fiber in the diet. Oat bran, oatmeal, beans, corn, and

fruits, such as apples, citrus fruits, and cranberries, are high in soluble fiber.

Minerals 1

Minerals are divided into major minerals and trace minerals. Major minerals are needed at quantities greater than 100 mg per day; trace, less than 100 mg. Major minerals—in cells and body fluids; are structural components of tissues. Trace minerals are often part of larger molecules. • That is, iron is present in hemoglobin, and iodine is a part

of thyroid hormones. • That is, zinc, copper, and manganese are present in

enzymes. 91

Minerals (Table 9.6) 1

Table 9.6a Minerals: Major (More than 100 mg/Day Needed) Mineral Functions Food Sources Health Concerns Deficiency Health Concerns Toxicity

Calcium (Ca raised to the 2 plus power) Strong bones and teeth, nerve conduction, muscle contraction, blood clotting

Dairy products, leafy green vegetables

Stunted growth in children, low bone density in adults

Kidney stones, interferes with iron and zinc absorption

Phosphorus (P O 4 raised to the 3 minus power) Bone and soft tissue growth; part of phospholipids, ATP, and nucleic acids

Meat, dairy products, sunflower seeds, food additives

Weakness, confusion, pain in bones and joints

Low blood and bone calcium levels

Potassium (K raised to the plus power) Nerve conduction, muscle contraction

Many fruits and vegetables, bran

Paralysis, irregular heartbeat, eventual death

Vomiting, heart attack, death

Sulfur (S raised to the 2 minus power) Stabilizes protein shape, neutralizes toxic substances

Meat, dairy products, legumes

Not likely In animals, depresses growth

Sodium (Na raised to the plus power) Nerve conduction, pH and water balance

Table salt Lethargy, muscle cramps, loss of appetite

Edema, high blood pressure

Chloride (Cl raised to the minus power) Water balance Table salt Not likely Vomiting, dehydration

Magnesium (Mg raised to the 2 plus power) Part of various enzymes for nerve and muscle contraction, protein synthesis

Whole grains, leafy green vegetables

Muscle spasm, irregular heartbeat, convulsions, confusion, personality changes

Diarrhea

Minerals (Table 9.6) 2

Table 9.6b Minerals: Trace (Less than 100 mg/Day Needed) Mineral Functions Food Sources Health Concerns Deficiency Health Concerns Toxicity Zinc (Zn raised to the 2 plus power) Protein synthesis, wound

healing, fetal development and growth, immune function

Meats, legumes, whole grains

Delayed wound healing, stunted growth, diarrhea, mental lethargy

Anemia, diarrhea, vomiting, renal failure, abnormal cholesterol levels

Iron (Fe raised to the 2 plus power) Hemoglobin synthesis Whole grains, meats, prune juice

Anemia, physical and mental sluggishness

Iron toxicity disease, organ failure, eventual death

Copper (Cu raised to the 2 plus power) Hemoglobin synthesis Meat, nuts, legumes Anemia, stunted growth in children

Damage to internal organs if not excreted

Iodine (I raised to the minus power) Thyroid hormone synthesis Iodized table salt, seafood Thyroid deficiency Depressed thyroid function, anxiety

Selenium (S e O 4 raised to the 3 minus power) Part of antioxidant enzyme Seafood, meats, eggs Vascular collapse, possible cancer development

Hair and fingernail loss, discolored skin

Manganese (Mn raised to the 2 plus power) Part of enzymes Nuts, legumes, green vegetables

Weakness and confusion Confusion, coma, death

Minerals 2

Minerals, continued. • Occasionally individuals do not receive enough iron,

calcium, magnesium, or zinc in their diets. • Adult females need more iron in their diet than

males because they lose hemoglobin each month during menstruation.

• A varied and complete diet usually supplies enough of each type of mineral.

Calcium

Calcium. • In bones, teeth. • Needed for nerve impulse conduction, muscle

contraction and blood clotting. • Calcium supplements prevent osteoporosis—a

degenerative bone disease common in the elderly. • Vitamin D is needed with calcium to prevent bone

loss.

Sodium

Sodium—regulates water balance. • Important in the movement of materials across the

plasma membrane as well as the conduction of a nerve impulse.

• The recommended amount of sodium intake per day is 1,500 mg, but the average American takes in more than 3,400 mg.

• Excess sodium can worsen hypertension.

Reducing Dietary Sodium (Table 9.7)

Table 9.7 Reducing Dietary Sodium To Reduce Dietary Sodium

• Use spices instead of salt to flavor foods. • Add little or no salt to foods at the table, and add only small amounts of

salt when you cook. • Eat unsalted crackers, pretzels, potato chips, nuts, and popcorn. • Avoid hot dogs, ham, bacon, luncheon meats, smoked salmon, sardines,

and anchovies. • Avoid processed cheese and canned or dehydrated soups. • Avoid brine-soaked foods, such as pickles and olives. • Read nutrition labels to avoid high-salt products.

Vitamins

Vitamins—organic compounds. • Used for metabolism. • Need to ingest, since they are not produced in high

enough quantities by the body. • Are often parts of coenzymes. • There are 13 vitamins, two types: fat soluble and

water soluble.

Fat-Soluble Vitamins (Table 9.8) Table 9.8 Fat-Soluble Vitamins

Vitamin Functions Food Sources Health Concerns Deficiency

Health Concerns Toxicity

Vitamin A Antioxidant synthesized from beta-carotene; needed for healthy eyes, skin, hair, and mucous membranes and for proper bone growth

Deep yellow/orange and leafy, dark green vegetables; fruits; cheese; whole milk; butter; eggs

Night blindness, impaired growth of bones and teeth

Headache, dizziness, nausea, hair loss, abnormal development of fetus

Vitamin D Group of steroids needed for development and maintenance of bones and teeth and for absorption of calcium

Milk fortified with vitamin D, fish liver oil; also made in the skin when exposed to sunlight

Rickets, decalcification and weakening of bones

Calcification of soft tissues, diarrhea, possible renal damage

Vitamin E Antioxidant that prevents oxidation of vitamin A and polyunsaturated fatty acids

Leafy green vegetables, fruits, vegetable oils, nuts, whole-grain breads and cereals

Unknown Diarrhea, nausea, headaches, fatigue, muscle weakness

Vitamin K Needed for synthesis of substances active in clotting of blood

Leafy green vegetables, cabbage, cauliflower

Easy bruising and bleeding

Can interfere with anticoagulant medication

Water-Soluble Vitamins (Table 9.9) 1

Table 9.9 Water-Soluble Vitamins (top) Vitamin Functions Food Sources Health Concerns

Deficiency Health Concerns Toxicity

Vitamin C Antioxidant; needed for forming collagen; helps maintain capillaries, bones, and teeth

Citrus fruits, leafy green vegetables, tomatoes, potatoes, cabbage

Scurvy, delayed wound healing, infections

Gout, kidney stones, diarrhea, decreased copper

Thiamine (vitamin B1)

Part of coenzyme needed for cellular respiration; also promotes activity of the nervous system

Whole-grain cereals, dried beans and peas, sunflower seeds, nuts

Beriberi, muscular weakness, enlarged heart

Can interfere with absorption of other vitamins

Riboflavin (vitamin B2)

Part of coenzymes, such as FAD; aids cellular respiration, including oxidation of protein and fat

Nuts, dairy products, whole- grain cereals, poultry, leafy green vegetables

Dermatitis, blurred vision, growth failure

Unknown

Niacin (nicotinic acid)

Part of coenzyme NAD; needed for cellular respiration, including oxidation of protein and fat

Peanuts, poultry, whole-grain cereals, leafy green vegetables, beans

Pellagra, diarrhea, mental disorders

High blood sugar and uric acid, vasodilation, etc.

Folacin (folic acid)

Coenzyme needed for production of hemoglobin and formation of DNA

Dark, leafy green vegetables; nuts; beans; whole-grain cereals

Megaloblastic anemia, spina bifida

May mask B12 deficiency

FAD = flavin adenine dinucleotide

NAD = nicotinamide adenine dinucleotide

100

Water-Soluble Vitamins (Table 9.9) 2

Table 9.9 Water-Soluble Vitamins (bottom) Vitamin Functions Food Sources Health Concerns

Deficiency Health Concerns Toxicity

Vitamin B6 Coenzyme needed for synthesis of hormones and hemoglobin; CNS control

Whole-grain cereals, bananas, beans, poultry, nuts, leafy green vegetables

Rarely, convulsions, vomiting, seborrhea, muscular weakness

Insomnia, neuropathy

Pantothenic acid

Part of coenzyme A needed for oxidation of carbohydrates and fats; aids in the formation of hormones and certain neurotransmitters

Nuts, beans, dark green vegetables, poultry, fruits, milk

Rarely, loss of appetite, mental depression, numbness

Unknown

Vitamin B12 Complex, cobalt-containing compound; part of the coenzyme needed for synthesis of nucleic acids and myelin

Dairy products, fish, poultry, eggs, fortified cereals

Pernicious anemia Unknown

Biotin Coenzyme needed for metabolism of amino acids and fatty acids

Generally in foods, especially eggs

Skin rash, nausea, fatigue

Unknown

101

Antioxidants

Antioxidants—decrease the rate of oxidation or transfer of electrons.

Cellular metabolism generates free radicals, which damage cells and tissues.

The most common free radicals in cells are superoxide 2(O ) and hydroxide (OH ).

Vitamin C, E, and A are considered antioxidants because they defend the body against free radicals. • Are common in fruits and vegetables.

102

2(O ) (OH ).

Vitamin D

Vitamin D. Skin cells contain a precursor that is converted to vitamin D after UV exposure.

Vitamin D is modified first in the kidneys and then in the liver until finally it becomes calcitriol. • Promotes the absorption of calcium by the intestines.

Lack of vitamin D leads to rickets in children. • Bowing of the legs, caused by defective mineralization of

the skeleton.

• Most milk is fortified with vitamin D to prevent rickets. 103

How to Plan Nutritious Meals 1

Basal metabolism—the number of calories a body burns at rest to maintain normal body functions. • Depending on exercise levels, someone may need

more calories beyond the basal metabolic rate. • A person cannot become overweight without taking

in more calories than needed.

104

How to Plan Nutritious Meals 2

Limit the number of calories to an amount used daily. • Woman—maximum number of daily calories

(without exercise) is 2,000. • Man—maximum 2,500 calories. • The MyPlate graphic shows how someone should

distribute those calories among the food groups.

105

The MyPlate Dietary Recommendations (Figure 9.15)

Access the text alternative for slide images.

U.S. Department of Agriculture 106

How to Plan Nutritious Meals 3

A diet should include foods from all food groups. Eat more of these foods: fruits, vegetables, whole grains, and fat-free or low-fat milk products. • Choose dark green vegetables, orange vegetables, and leafy

vegetables.

• Dry beans and peas are good sources of fiber and an excellent protein source as well.

• Limit potatoes and corn.

• When eating grains, choose whole grains, such as brown rice, oatmeal, and whole-wheat bread.

• Choose fruit as a snack or a topping for foods, instead of sugar.

107

How to Plan Nutritious Meals 4

A diet should include, continued. Choose lean meats, such as poultry, and fish high in omega-3 fatty acids, such as salmon, trout, and herring, in moderate- sized portions. • Include oils rich in monounsaturated and polyunsaturated fatty acids

in the diet.

Eat less of foods high in saturated or trans fats, added sugars, cholesterol, salt, and alcohol.

Be physically active every day.

108

Eating Disorders 1

Eating disorders have social, cultural, emotional, and biological roots.

Anorexia nervosa—psychological disorder; a fear of getting fat. • Usually results in self-induced starvation, high physical

activity, and may include purging.

Bulimia nervosa—eat large amounts of high-calorie food (binge-eating) followed by purging to avoid weight gain.

109

Eating Disorders 2

Eating disorders, continued. Binge-eating disorder—overeating without purging. • Stress, anxiety, anger, and depression can contribute.

• Common in the obese.

110

Eating Disorders 3

Eating disorders, concluded. Muscle dysmorphia—thinks his or her body is underdeveloped. • Excess body-building.

• A preoccupation with diet and body form.

• May spend hours in the gym every day.

• Unlike anorexia nervosa and bulimia, affects more men than women.

111

Check Your Progress 9.6

Briefly describe and give an example of each class of nutrients. Discuss why carbohydrates and fats might be the cause of the obesity epidemic today. Explain the difference between a vitamin and mineral.

112

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End of Main Content

human Biology Seventeenth Edition
9.1 Overview of Digestion 1
9.1 Overview of Digestion 2
Organs of the GI Tract and Accessory Structures of Digestion (F
Processes of Digestion
Stages of Digestion
Wall of the Digestive Tract 1
The Layers of the Gastrointestinal Tract Wall (Figure 9.2)
Wall of the Digestive Tract 2
Bowel Disease
Check Your Progress 9.1
9.2 The Mouth, Pharynx, and Esophagus
The Mouth 1
Structures of the Mouth (Figure 9.3a) 1
The Mouth 2
The Mouth 3
The Mouth 4
Structures of the Mouth (Figure 9.3b) 2
The Mouth 5
The Pharynx and Esophagus
Swallowing
The Process of Swallowing (Figure 9.4)
Peristalsis 1
Peristalsis 2
Check Your Progress 9.2
9.3 The Stomach and Small Intestine
The Stomach 1
Structure of the Stomach (Figure 9.5)
The Stomach 2
The Stomach 3
The Stomach 4
The Small Intestine 1
The Small Intestine 2
The Small Intestine 3
Major Digestive Enzymes (Table 9.1) 1
Major Digestive Enzymes (Table 9.1) 2
The Small Intestine 4
Absorption in the Small Intestine (Figure 9.6)
The Small Intestine 5
Digestion and Absorption of Organic Nutrients (Figure 9.7)
Lactose Intolerance
Celiac Disease
Check Your Progress 9.3
9.4 The Accessory Organs and Regulation of Secretions
The Accessory Organs 1
Accessory Organs of the Digestive System (Figure 9.8)
The Accessory Organs 2
The Accessory Organs 3
Functions of the Liver (Table 9.2)
The Accessory Organs 4
The Accessory Organs 5
The Accessory Organs 6
Liver Disorders
Hepatitis
Cirrhosis
Regulation of Digestive Secretions 1
Hormonal Control and Regulation of Digestion (Figure 9.9)
Regulation of Digestive Secretions 2
Check Your Progress 9.4
9.5 The Large Intestine and Defecation
The Large Intestine 1
The Regions of the Large Intestine (Figure 9.10)
The Large Intestine 2
Functions of the Large Intestine 1
Functions of the Large Intestine 2
Functions of the Large Intestine 3
Disorders of the Colon and Rectum 1
Disorders of the Colon and Rectum 2
Disorders of the Colon and Rectum 3
Disorders of the Colon and Rectum 4
Check Your Progress 9.5
9.6 Nutrition and Weight Control 1
9.6 Nutrition and Weight Control 2
Defining Obesity
BMI Values (Table 9.3)
The Body Mass Index Chart (Figure 9.11)
Classes of Nutrients
Carbohydrates 1
Carbohydrates 2
Carbohydrates 3
Reducing High-Glycemic-Index Carbohydrates (Table 9.4)
Proteins 1
Proteins 2
Lipids 1
Lipids 2
Saturated and Unsaturated Fatty Acids (Figure 9.14)
Lipids 3
Lipids 4
Reducing Lipids in the Diet (Table 9.5) 1
Reducing Lipids in the Diet (Table 9.5) 2
Minerals 1
Minerals (Table 9.6) 1
Minerals (Table 9.6) 2
Minerals 2
Calcium
Sodium
Reducing Dietary Sodium (Table 9.7)
Vitamins
Fat-Soluble Vitamins (Table 9.8)
Water-Soluble Vitamins (Table 9.9) 1
Water-Soluble Vitamins (Table 9.9) 2
Antioxidants
Vitamin D
How to Plan Nutritious Meals 1
How to Plan Nutritious Meals 2
The MyPlate Dietary Recommendations (Figure 9.15)
How to Plan Nutritious Meals 3
How to Plan Nutritious Meals 4
Eating Disorders 1
Eating Disorders 2
Eating Disorders 3
Check Your Progress 9.6
End of Main Content