Chapter 9

Question 1

List and describe the four stages of the digestive process.

Answer 1

The four stages of the digestive process are:
1) Ingestion occurs when the mouth takes in food.
2) Digestion involves the breakdown of larger pieces of food into smaller pieces that digestive enzymes can act on.
3) Absorption occurs as subunit molecules cross the GI tract wall and enter cells.
4) Elimination removes indigestible molecules and discharges them from the body.

Question 2

Briefly describe the structure of the mouth. What is the function of the mouth? Distinguish between
mechanical digestion and chemical digestion. What is the function of salivary amylase?

Answer 2

The mouth, pharynx, and esophagus are in the first part of the GI tract.
The Mouth
A roof, formed by the hard and soft palates, separates the mouth from the nasal cavities. The mouth receives food and begins the process of mechanical and chemical digestion. Three pairs of salivary glands secrete saliva (containing salivary amylase for digestion of starch) into the mouth.

Question 3

What is a bolus?

Answer 3

Mechanical digestion begins when the teeth chew the food and the tongue forms a bolus for swallowing.

Question 4

Name the two parts that each tooth has. Distinguish among enamel, dentin, and pulp

Answer 4

Each tooth has a crown and a root. The crown has a layer of enamel, dentin, and an inner pulp. The root has dentin and pulp. Blood vessels and nerves are in the pulp

Question 5

What are some ailments associated with the teeth?

Answer 5

Gum disease and dental caries are two ailments associated with the teeth.

Question 6

What type of muscle composes the tongue? What are the sensory receptors of the tongue?

Answer 6

The tongue is composed of skeletal muscle, and it is covered by a mucous membrane that contains the sensory receptors called taste buds.

Question 7

What is the pharynx? What is the function of the esophagus?

Answer 7

The air and food passages, two tubes that run parallel to one another, cross in the pharynx, which is a hollow space at the back of the throat. The esophagus is the long tube that takes food to the stomach.

Question 8

What does the epiglottis do when we swallow? Can we breathe and swallow at the same time? Why or why not?

Answer 8

When one swallows, the air passage is usually blocked off by the epiglottis and food must enter the esophagus. We do not breathe when we swallow.

Question 9

What is peristalsis? Where does it occur in the digestive tract?

Answer 9

A rhythmic contraction called peristalsis pushes food along the esophagus and continues in all the organs of the digestive tract.

Question 10

What are sphincters? What is their function?

Answer 10

Sphincters are muscles that encircle tubes and act as valves. The tubes close when the sphincters contract and open when they relax.

Question 11

What is heartburn and what causes it?

Answer 11

When food moves from the stomach back into the esophagus, heartburn occurs.

Question 12

What happens physically in the digestive system that causes vomiting?

Answer 12

When strong contractions of the abdominal muscles and the diaphragm force the stomach contents into the esophagus and oral cavity, vomiting occurs.

Question 13

What is the function of the stomach? What is chyme? What are rugae?

Answer 13

The stomach expands and stores food. While food is in the stomach, the stomach churns, mixing the food with its acidic gastric juices (containing HCl and pepsin for the digestion of protein) to produce chyme. Few materials are absorbed through the stomach lining. Besides the circular and longitudinal layers of stomach smooth muscle, the oblique layer allows the stomach to stretch and mechanically break down food. Deep folds called rugae disappear when the stomach fills. Peristaltic waves move food toward the pyloric sphincter.

Question 14

What is the function of the small intestine?

Answer 14

The small intestine is smaller in diameter than the large intestine but is actually longer.

Question 15

Why do you suppose pancreatic juice is alkaline (basic)? What are the functions of: lipase, pancreatic amylase, and pancreatic trypsin?

Answer 15

Digestion Is Completed in the Small Intestine
The small intestine contains enzymes to digest all types of foods. The duodenum receives bile from the gallbladder and pancreatic enzymes. Pancreatic juice is basic because of the presence of NaHCO3. Lipase is a pancreatic enzyme that hydrolyzes fat, and pancreatic amylase digests carbohydrates. Pancreatic trypsin and other intestinal proteases complete protein digestion.

Question 16

What are villi? Where would you find them and what is their function? What are lacteals?

Answer 16

Nutrients Are Absorbed in the Small Intestine
The walls of the small intestine absorb the sugar, amino acid, glycerol, and fatty acid molecules that were products of digestion. They have fingerlike projections called villi, where nutrient molecules are absorbed into the cardiovascular and lymphatic systems. The lymphatic capillary in a villus is called a lacteal. Lipoprotein molecules called chylomicrons enter lacteals. Nutrients are carried to all cells of the body by the bloodstream.

Question 17

What is the cause of lactose intolerance? What are the symptoms?

Answer 17

Lactose Intolerance
Lactose is the primary sugar in milk. Some people are not able to digest lactose because they are missing the enzyme lactase. Lactose intolerance is characterized by diarrhea, gas, bloating, and abdominal cramps after consuming milk or other dairy products. A dietary supplement is available to prevent these symptoms.

Question 18

What is the cause of celiac disease? What are the symptoms? What foods do people with celiac disease
need to avoid?

Answer 18

An autoimmune response to a protein called gluten is what causes celiac disease. Grains such as wheat, barley, and rye contain gluten. People with celiac disease experience abdominal discomfort and diarrhea from the inflammatory response in the small intestine that can damage villi and microvilli. Gluten sensitivity is a less severe condition in which symptoms may be the same but damage to the villi and microvilli is not present. Those without celiac disease or sensitivity will receive no benefit from a gluten-free diet.

Question 19

Describe the basic function of the following accessory organs of digestion: pancreas, liver, gallbladder.

Answer 19

The Accessory Organs
The three accessory organs of digestion—the pancreas, liver, and gallbladder—send secretions to the duodenum via ducts. The pancreas produces pancreatic juice, which contains digestive enzymes to break down carbohydrates (pancreatic amylase), proteins (trypsin), and fats (lipase). The liver produces bile, which is stored in the gallbladder. The liver receives blood from the small intestine by way of the hepatic portal vein. It has numerous important functions, and any malfunction of the liver is a matter of considerable concern. The gallbladder stores bile until it is sent to the duodenum.

Question 20

What is insulin? Where is it produced? What is the function of insulin?

Answer 20

Gallstones are crystals of cholesterol. The pancreas also secretes the hormone insulin into the blood. Insulin helps bring the level of blood glucose under control.

Question 21

What is diabetes?

Answer 21

Diabetes occurs when the pancreas does not produce sufficient amounts of insulin.

Question 22

Briefly describe the following liver disorders: hepatitis, cirrhosis, jaundice.

Answer 22

Hepatitis and cirrhosis are two serious diseases that affect the entire liver and hinder its ability to repair itself. Jaundice is a yellowish tint to the eyes that occurs when bile pigments leak into the blood due to a liver ailment. The liver is capable of regeneration except during liver failure.

Question 23

How are secretions of digestive juices controlled?

Answer 23

The secretions of digestive juices are controlled by the nervous system and by digestive hormones. The parasympathetic nervous system automatically stimulates gastric secretion when you look at or smell food. The stomach and duodenal wall produce hormones that regulate digestion, particularly CCK, secretin, and gastrin.

Question 24

List the parts of the large intestine. What is the appendix?

Answer 24

The large intestine consists of the cecum, colon (ascending, transverse, descending, and sigmoid), and the rectum, which ends at the anus. The cecum contains the appendix, which is thought to aid in fighting infections.

Question 25

What is the function of the large intestine? What is defecation?

Answer 25

The large intestine absorbs water, salts, and some vitamins, and it forms and stores feces. Defecation, which is ridding the body of feces, is also a function of the large intestine. The consistency of normal feces is three-fourths water and one-fourth solid wastes. Bacteria, dietary fiber, and other indigestible materials make up the solid wastes. Stercobilin is a breakdown product of bilirubin, a bile pigment produced from hemoglobin breakdown that causes the brown color of feces.

Question 26

Briefly define or describe the following disorders of the colon and rectum: diarrhea, constipation, Hemorrhoids, diverticulosis, irritable bowel syndrome, inflammatory bowel disease, polyps and cancer.

Answer 26

Disorders of the Colon and Rectum Many of these disorders can be prevented or minimized by a good diet and proper hygiene. Diarrhea The major causes of diarrhea are infection of the lower intestinal tract and nervous stimulation. Constipation When a person is constipated, the feces are dry and hard. An intake of water and fiber can help the regularity of defecation. Chronic constipation is associated with hemorrhoid development. Diverticulosis Diverticulosis is the occurrence of little pouches of mucosa that have pushed out through weak spots in the muscularis. Irritable Bowel Syndrome IBS is a condition in which the muscularis contracts powerfully but without its normal coordination. Inflammatory Bowel Disease This is a collective term for a number of inflammatory disorders including ulcerative colitis and Crohn’s disease. Polyps and Cancer Polyps are small growths arising from the epithelial lining, which may be benign or cancerous. Some investigators believe that dietary fat increases the likelihood of colon cancer. An endoscopic exam called a colonoscopy allows a doctor to examine the colon.

Question 27

With reference to body mass index (BMI), how is obesity defined?

Answer 27

Obesity has become one of the biggest health problems in the United States, and it is on the rise around the world. Defining Obesity Obesity is often defined as having a body mass index (BMI) of 30 or greater. Figure 9.11 on page 184 of the text will help you determine your BMI.

Question 28

Define nutrient. List the functions of the following classes of nutrients in the diet: carbohydrates, proteins, lipids. Which types of these nutrients do dietitians recommend avoiding if you are following a healthy diet?

Answer 28

A nutrient is defined as a component of food that performs a physiological function in the body. Carbohydrates To meet energy needs, dietitians recommend consuming foods rich in complex carbohydrates like breads and pasta. Simple carbohydrates like table sugar (sucrose) are not recommended. Fiber helps regularity and may help prevent cancer. Can Carbohydrates Be Harmful? Some nutritionists hypothesize that the high intake of refined carbohydrates and fructose sweeteners processed from cornstarch may be responsible for obesity. These foods have a high glycemic index because the blood glucose response to these foods is high, potentially leading to insulin resistance. Proteins Eating meat ensures that all the essential amino acids are acquired, but this is also possible by consuming a combination of legumes, grains, vegetables, seeds, and nuts. Can Proteins Be Harmful? The body can be harmed if the amount of protein in the diet is severely limited or if it is present in an overabundance. The average American eats about twice as much protein as needed. Dehydration can occur if protein consumption is excessive. Certain types of meat are known to be high in saturated fats, which is a risk factor for cardiovascular disease. Lipids Fats, oils, and cholesterol are lipids. Saturated fats, which are usually solid at room temperature, promote heart disease. Oils contain unsaturated fatty acids, which do not promote cardiovascular disease. Linoleic and linolenic acids are essential fatty acids and must be supplied by diet. Can Lipids Be Harmful? Lipids should be used sparingly because they contribute to plaque on blood vessel walls. Trans fatty acids arise when unsaturated fatty acids are hydrogenated to produce a solid fat. Trans fats may contribute to cholesterol in the blood. Cholesterol is carried in the blood by two transport proteins, HDL and LDL. HDL transports cholesterol to the liver, where it is metabolized, but LDL- carried cholesterol winds up in tissues, allowing the formation of plaques.

Question 29

What are functions and/or concerns about the following minerals in the diet? iron, calcium, sodium

Answer 29

Minerals are divided into major minerals and trace minerals. Major minerals are constituents of cells and body fluids and are structural components of tissues. Trace minerals are parts of larger molecules. Females need more dietary iron than males because they lose hemoglobin each month. Calcium Calcium is needed to have strong bones, and older women in particular are at risk for osteoporosis, a degenerative bone disease due to insufficient intake of calcium and/or uptake of calcium by their bones. Sodium Most Americans have too much sodium in their diet. Salt intake leads to hypertension in some people.

Question 30

What are vitamins? What are some of their functions?

Answer 30

Vitamins are organic compounds that the body is unable to produce but needs for metabolic purposes. Many vitamins are portions of coenzymes. Vitamins are divided into fat- and water-soluble classes. Antioxidants Vitamins A, E, and C are antioxidants that protect cell contents from damage due to free radicals. Dietary supplements may provide a safeguard against cancer and cardiovascular disease. Vitamin D A precursor molecule in skin is converted to vitamin D after exposure to UV light rays. Vitamin D is modified first in the kidneys and then the liver until calcitriol results. Calcitriol is needed for calcium absorption. Most milk is fortified with vitamin D, which prevents rickets.

Question 31

What is the food pyramid?

Answer 31

The new food pyramid can be used to help you decide how your daily calories should be distributed among the foods to eat. The new guidelines developed by the U.S. Department of Agriculture are called MyPlate (Figure 9.15 on page 192 of the text). Proper diet should be accompanied by daily physical activity.

Question 32

Describe the following eating disorders/body image problems: obesity, anorexia nervosa, bulimia, muscle dysmorphia.

Answer 32

People with eating disorders are dissatisfied with their body image. Severe conditions such as obesity, anorexia nervosa, muscle dysmorphia, and bulimia can lead to malnutrition, disability, and death. Muscle dysmorphia affects more men than women.