1. gustatory cells: Surface cells in the throat and on the taste buds in the mouth that transmit

Transcription

1 Chapter 3 Digestion and Absorption Key Terms 1. gustatory cells: Surface cells in the throat and on the taste buds in the mouth that transmit taste information. 2. absorption: The movement of substances into or across tissues; in particular, the passage of nutrients and other substances into the walls of the gastrointestinal tract and then into the bloodstream. 3. chemosenses: The chemical sensing system in the body, including taste and smell. 4. amylase: A salivary enzyme that catalyzes the hydrolysis of amylose, a starch. 5. villi: Small, fingerlike projections that blanket the folds in the lining of the small intestine. 6. chyme: A mass of partially digested food and digestive juices moving from the stomach into the small intestine. 7. cholecystokinin (CCK): A hormone produced by cells in the small intestine that stimulate the release of digestive enzymes from the pancreas and bile from the gallbladder. 8. esophagus: The food pipe that extends from the pharynx to the stomach. 9. catalyze: To speed up a chemical reaction. 10. diarrhea: Watery stools due to reduced absorption of water. 11. concentration gradient: A difference between the solute concentrations of two substances. 12. flatus: Lower intestinal gas that is expelled through the rectum. 13. lumen: Cavity or hollow channel in any organ or structure of the body.

2 14. gastrin: A hormone released from the walls of the stomach and duodenum that stimulates gastric secretions and motility. 15. segmentation: A series of muscular contractions that occur in the small intestine, thereby dividing and mixing chyme. 16. mucosa: The lining of the gastrointestinal tract, also called the intestinal wall. It is composed of epithelial cells and glands. 17. ulcer: A craterlike lesion that occurs in the lining of the stomach or duodenum. 18. bolus: A chewed, moistened lump of food that is ready to be swallowed. 19. passive diffusion: The movement of substances into or out of cells without the expenditure of energy or the involvement of transport proteins in the cell membrane. Also called simple diffusion. 20. intrinsic factor: A protein released from cells in the stomach wall that binds to and aids in absorption of vitamin B hydrochloric acid: A very strong acid of chloride and hydrogen atoms made by stomach glands and secreted into the stomach. Also called gastric acid. 22. sphincters: Circular bands of muscle fibers that surround the entrance or exit of a hollow body structure (e.g., the stomach) and act as valves to control the flow of material. 23. acrolein: A pungent decomposition product of fats, generated from dehydrating the glycerol component of fats; responsible for the coughing attacks caused by the fumes released by burning fat. This toxic water-soluble liquid vaporizes easily and is highly flammable. 24. pepsinogen: The inactive form of the enzyme pepsin. 25. hydrolysis: A reaction that breaks apart a compound through the addition of water.

3 26. ileum: The terminal segment of the small intestine (about 150 cm [5 ft] long), which opens into the large intestine. 27. digestion: The process of transforming the foods we eat into units for absorption. 28. emulsifiers: Agents that blend fatty and watery liquids by promoting the breakup of fat into small particles and stabilizing their suspension in a watery solution. 29. irritable bowel syndrome: A disruptive state of intestinal motility with no known cause. 30. bile: An alkaline, yellow-green fluid that is produced in the liver and stored in the gallbladder. It emulsifies dietary fats, aiding fat digestion and absorption. 31. circular muscle: Layers of smooth muscle that surround organs, including the stomach and the small intestine. 32. gallbladder: A pear-shaped sac that stores and concentrates bile from the liver. 33. enzymes: Proteins in the body that speed up the rate of chemical reactions but are not altered in the process. 34. mucus: A slippery substance secreted in the GI tract (and other body linings) that protects cells from irritants. 35. microvilli: Minute, hairlike projections that extend from the surface of absorptive cells facing the intestinal lumen. 36. longitudinal muscle: Muscle fibers aligned lengthwise. 37. pepsin: A protein-digesting enzyme produced by the stomach. 38. dyspepsia: A condition also known as upset stomach or indigestion; refers to difficulty with digestion.

4 Fill-in-the-Blank 1. Also called the preabsorptive phase responses, the cephalic phase responses are those responses of the parasympathetic nervous system to the sight, smell, thought, and sound of food. 2. The common chemical sense is a chemosensory mechanism that contributes to our senses of smell and taste. It comprises thousands of nerve endings, especially on the moist surfaces of the eyes, nose, mouth, and throat. 3. The central nervous system (CNS) consists of the brain and the spinal cord. It transmits signals that control muscular actions and glandular secretions along the entire gastrointestinal (GI) tract. 4. Chronic pain in the upper abdomen not due to any obvious physical cause is called functional dyspepsia. 5. Diverticulosis occurs when small pouches push outward through weak spots in the colon. 6. The movement of substances into or out of cells against a concentration gradient is called active transport. This requires energy and involves carrier proteins in the cell membrane. 7. Lingual lipase is a fat-splitting enzyme secreted by cells at the base of the tongue. 8. The part of the central nervous system that regulates the automatic responses of the body is the autonomic nervous system. 9. The enteric nervous system is a network of nerves located in the GI wall. 10. The largest glandular organ in the body, the liver, produces and secretes bile, detoxifies harmful substances, and helps metabolize carbohydrates, lipids, proteins, and micronutrients.

5 11. Elimination is a term that refers to the removal of undigested food from the body. 12. The esophageal sphincter is the opening between the esophagus and the stomach that relaxes and opens to allow the bolus to travel into the stomach, and then closes behind it. It also acts as a barrier to prevent the reflux of gastric contents. 13. The middle section of the small intestine (about 120 cm [4ft] long), lying between the duodenum and ileum, is the jejunum. 14. Infrequent and difficult bowel movements, followed by a sensation of incomplete evacuation, is called constipation. 15. The vascular system is a network of veins and arteries through which the blood carries nutrients. It is also called the blood circulatory system. 16. Facilitated diffusion is a process by which carrier (transport) proteins in the cell membrane transport substances into or out of cells down a concentration gradient. 17. Recycling of certain compounds between the small intestine and the liver is called enterohepatic circulation. 18. The gastrointestinal (GI) tract is the connected series of organs and structures used for digestion of food and absorption of nutrients. 19. The sphincter at the junction of the small and large intestines is the ileocecal valve. 20. Tissue damage to the esophagus due to the reflux of gastric contents is known as gastroesophageal reflux disease (GERD). 21. The lacteal is a small lymphatic vessel in the interior of each intestinal villus that picks up fat-soluble compounds from intestinal cells. 22. Gastric lipase is an enzyme in the stomach that primarily breaks down butterfat.

6 23. The pancreas secretes enzymes that affect the digestion and absorption of nutrients and releases hormones, such as insulin, that regulate metabolism as well as the way nutrients are used in the body. 24. The hormone gastric inhibitory peptide is released from the walls of the duodenum and slows the release of the stomach contents into the small intestine and stimulates release of insulin from the pancreas. 25. The lymphatic system is a system of small vessels, ducts, valves, and organized tissue (e.g., lymph nodes) through which lymph moves from its origin in the tissues toward the heart. 26. Peristalsis is the wavelike, rhythmic muscular contractions of the GI tract that propel its contents down the tract. 27. The pyloric sphincter is a circular muscle that forms the opening between the duodenum and the stomach. It regulates the passage of food into the small intestine. 28. The enlarged, muscular, saclike portion of the digestive tract between the esophagus and the small intestine is the stomach. It has a capacity of about 1 quart. 29. The tube (approximately 3 meters [10 ft] long) where the digestion of protein, fat, and carbohydrate is completed and where the majority of nutrients are absorbed is the small intestine. It is divided into three parts: the duodenum, the jejunum, and the ileum. 30. Salivary glands are glands in the mouth that release saliva. 31. ph is a measurement of the hydrogen ion concentration, or acidity, of a solution. 32. The blind pouch at the beginning of the large intestine into which the ileum opens from one side and which is continuous with the colon is called the cecum. 33. The portion of the large intestine extending from the cecum to the rectum is the colon.

7 34. The large intestine is the tube (about 150 cm [5 ft] long) extending from the ileum of the small intestine to the anus. It includes the appendix, cecum, colon, rectum, and anal canal. 35. Digestive secretions are substances released at different places in the GI tract to speed the breakdown of ingested carbohydrates, fats, and proteins. 36. Burning pain behind the breastbone area caused by acidic stomach contents backing up into the esophagus is called heartburn. 37. The duodenum is the portion of the small intestine closest to the stomach. It is 25 to 30 cm (10 to 12 in.) long and wider than the remainder of the small intestine. 38. Fluid that travels through the lymphatic system, made up of large fat particles and fluid drained from the areas between cells, is called lymph. 39. The process of separating and removing waste products of metabolism is excretion. Fill-in-the-Blank Summaries Putting It All Together: Digestion and Absorption The digestive process begins in the mouth. Chewing breaks food into smaller pieces, increasing the surface area available to enzymes. Saliva contains the enzyme amylase, which breaks down starch into small sugar molecules. In the mouth, saliva and mucus blend with the food to form a bolus. This ball of chewed food then slides through the esophagus to the stomach. Once in the stomach, the esophageal sphincter keeps the food from sliding back into the esophagus. Hydrochloric acid creates an acidic environment in the stomach that kills many pathogenic bacteria and aids in the digestion of protein. When the chyme is ready to leave the stomach, about percent of carbohydrate, percent of protein,

8 and less than 10 percent of fat have been digested. Very little absorption occurs in the stomach. In the small intestine, most digestion takes place in the duodenum. Fats do not usually mix with water, but this process is facilitated by bile once it is released from the gallbladder into the duodenum. Nutrients absorbed through the intestinal lining pass into the interior of the villi. Each villus contains blood vessels and a lacteal. Most minerals, with the exception of potassium, sodium, and chloride, are absorbed in the small intestine. Undigested material and some liquid move on to the large intestine, where water and electrolytes are absorbed, leaving waste material to be excreted as feces. Nutrition and GI Disorders A diet low in fiber and water and high in fat is the most common cause of constipation. As people age, the colon develops small pouches that bulge outward through weak spots. This condition is known as diverticulosis. Eating a diet high in fiber can help prevent this condition. GERD occurs when the lower esophageal sphincter relaxes inappropriately. The esophagus has no protective mucous lining, so acid can quickly damage it. Doctors recommend avoiding foods that can weaken this sphincter, such as peppermint. The cause of IBS remains a mystery. Some foods that are often offenders are beans and chocolate. Without treatment, IBS will not progress to a more serious illness. It is likely that a number of physical and psychosocial factors combine to trigger this disorder. After lung cancer, colon cancer is the most common form of cancer in the United States. Research to date shows that diets high in vegetables and regular physical activity are the most significant factors in reducing risk of this type of cancer. Flatus composition depends largely on carbohydrate intake and the activity of the colon s bacterial population. The major cause

9 of ulcers is Helicobacter pylori, which creates ulcers by weakening the protective mucus coating around the lining of the stomach. Short Answer 1. The GI tract has a large variety of functions. Explain the six primary functions. 1. Ingestion the receipt and softening of food 2. Transport of digested food 3. Secretion of digestive enzymes, acid, mucus, and bile 4. Absorption of end products of digestion 5. Movement of undigested material 6. Elimination the transport, storage, and excretion of waste products 2. In addition to enzymes, other chemicals support the digestive process. List these four chemicals. Acid in the stomach; neutralizing base in the small intestine; bile that prepares fat for digestion; mucus secreted along the GI tract 3. How does eating a high fiber diet help to prevent constipation? Some fibers dissolve easily in water and take on a soft, gel-like texture in the intestine. Other fibers pass along unchanged through the intestines. The bulk and soft texture of fiber help prevent hard, dry stools that are difficult to pass. 4. The digestion of protein, fat, and nearly all carbohydrates is completed and most nutrients are absorbed in which part of the digestive tract? Small intestine

10 5. Which body organ is considered the chemical factory, performing over 500 chemical functions that include the production of blood proteins, cholesterol, and sugars? Liver 6. Which nutrients are absorbed into the lymph system in the small intestine and leave the GI tract bypassing the liver? Fat-soluble nutrients and most end products of fat digestion 7. What substance present in a healthy stomach helps prevent foodborne illnesses? Hydrochloric acid 8. Identify four ways you can prevent and manage most GI disorders. Add fiber-rich foods and water to your diet; exercise; manage stress; maintain a healthy weight Labeling Identify the structural organization of the GI tract wall. Serosa; Longitudinal muscle; Circular muscle; Mucosa; Submucosa; Lumen