1. A 21-year-old woman visits her physician because of nausea, diarrhea, light-headedness, and flatulence. After an overnight fast, the physician administers 50 grams of oral lactose at time zero (indicated by the arrows in the above figure). Which combination is most likely in this patient during the next 3 hours? A) A B) B C) C D) D
1. B) Patients with a lactase deficiency cannot digest milk products that contain lactose (milk sugar). The operons of gut bacteria quickly switch over to lactose metabolism, which results in fermentation that produces copious amounts of gas (a mixture of hydrogen, carbon dioxide, and methane). This gas, in turn, may cause a range of abdominal symptoms including stomach cramps, bloating, and flatulence. The gas is absorbed by blood (especially in the colon) and exhaled from the lungs. Blood glucose levels do not increase because lactose is not digested to glucose and galactose in these patients.
2. A 43-year-old man eats a meal consisting of 40 percent protein, 10 percent fat, and 50 percent carbohydrate. Thirty minutes later the man feels the urge to defecate. Which reflex results in the urge to defecate when the duodenum is stretched? A) Duodenocolic B) Enterogastric C) Intestino-intestinal D) Rectosphincteric
2. A) The appearance of mass movements after meals is facilitated by gastrocolic and duodenocolic reflexes. These reflexes result from distention of the stomach and duodenum. They are greatly suppressed when the extrinsic autonomic nerves to the colon have been removed; therefore, the reflexes are likely transmitted by way of the autonomic nervous system. All the gut reflexes are named with the anatomical origin of the reflex as the prefix followed by the name of the gut segment in which the outcome of the reflex is observed. For example, the duodeno-colic reflex begins in the duodenum and ends in the colon. When the duodenum is distended, nervous signals are transmitted to the colon, which stimulates mass movements. The enterogastric reflex occurs when signals originating in the intestines inhibit gastric motility and gastric secretion. The intestino-intestinal reflex occurs when overdistention or injury to a bowel segment signals the bowel to relax. The rectosphincteric reflex, also called the defecation reflex, is initiated when feces enters the rectum and stimulates the urge to defecate.
3. A 23-year-old man consumes a meal containing 30 percent protein, 15 percent fat, and 55 percent carbohydrate. At which of the locations depicted in the above figure are bile salts most likely to be absorbed by an active transport process? A) A B) B C) C D) D E) E
3. D) About 94 percent of the bile salts are reabsorbed into the blood from the small intestine, with about half of this by diffusion through the mucosa in the early portions of the small intestine and the remainder by an active transport process through the intestinal mucosa in the distal ileum.
4. The ileum and distal jejunum of a 34-year-old man are ruptured in an automobile accident. The entire ileum and a portion of the jejunum are resected. What is most likely to occur in this man? A) Atrophic gastritis B) Constipation C) Gastric ulcer D) Gastroesophageal reflux disease (GERD) E) Vitamin B12 deficiency
4. E) Vitamin B12 is absorbed in the ileum; this absorption requires intrinsic factor, which is a glycoprotein secreted by parietal cells in the stomach. Binding of intrinsic factor to dietary vitamin B12 is necessary for attachment to specific receptors located in the brush border of the ileum. Atrophic gastritis is a type of autoimmune gastritis that is mainly confined to the acidsecreting corpus mucosa. The gastritis is diffuse, and severe atrophy eventually develops. Ileal resection is likely to cause diarrhea but not constipation. A gastric ulcer is possible but relatively unlikely. GERD is caused by gastric acid and bile reflux into the esophagus; mucosal damage and epithelial cell transformation lead to Barrett esophagus, which is a forerunner to adenocarcinoma, a particularly lethal cancer
5. Which ion has the highest concentration in saliva under basal conditions? A) Bicarbonate B) Chloride C) Potassium D) Sodium
5. A) Although the potassium concentration in saliva is about seven times greater than that of plasma, and the bicarbonate concentration in saliva is only about three times greater than that of plasma, the actual concentration of bicarbonate in saliva is 50 to 70 mEq/L, whereas the concentration of potassium is about 30 mEq/L, under basal conditions.
6. A 10-year-old boy consumes a cheeseburger, fries, and chocolate shake. The meal stimulates the release of several gastrointestinal hormones. The presence of fat, carbohydrate, or protein in the duodenum stimulates the release of which hormone from the duodenal mucosa? A) Cholecystokinin (CCK) B) Glucose-dependent insulinotropic peptide (GLIP) C) Gastrin D) Motilin E) Secretin
6. B) GLIP is the only gastrointestinal hormone released by all three major foodstuffs (fats, proteins, and carbohydrates). The presence of fat and protein in the small intestine stimulates the release of CCK, but carbohydrates do not stimulate its release. The presence of protein in the antrum of the stomach stimulates the release of gastrin, but fat and carbohydrates do not stimulate its release. Fat has a minor effect to stimulate the release of motilin and secretin, but neither hormone is released by the presence of protein or carbohydrate in the gastrointestinal tract.
7. A clinical experiment is conducted in which one group of subjects is given 50 grams of glucose intravenously and another group is given 50 grams of glucose orally. Which factor can explain why the oral glucose load is cleared from the blood at a faster rate compared with the intravenous glucose load? A) CCK-induced insulin release B) CCK-induced vasoactive intestinal peptide (VIP) release C) GLIP-induced glucagon release D) GLIP-induced insulin release E) VIP-induced GLIP release
7. D) GLIP is released by the presence of fat, carbohydrate, or protein in the gastrointestinal tract. GLIP is a strong stimulator of insulin release and is responsible for the observation that an oral glucose load releases more insulin and is metabolized more rapidly than an equal amount of glucose administered intravenously. Intravenously administered glucose does not stimulate the release of GLIP. Neither CCK nor VIP stimulates the release of insulin. GLIP does not stimulate glucagon release, and glucagon has the opposite effect of insulin; that is, it would decrease the rate of glucose clearance from the blood. VIP does not stimulate GLIP release.
8. Digestion of which of the following is impaired to the greatest extent in patients with achlorhydria? A) Carbohydrate B) Fat C) Protein
8. C) Achlorhydria means simply that the stomach fails to secrete hydrochloric acid. This condition is diagnosed when the pH of the gastric secretions fails to decrease below 4 after stimulation by pentagastrin. When acid is not secreted, pepsin also usually is not secreted. Even when it is, the lack of acid prevents it from functioning because pepsin requires an acid medium for activity. Thus, protein digestion is impaired.
9. A 33-year-old man visits his physician because his chest hurts when he eats, especially when he eats meat. He also belches excessively and has heartburn. His wife says he has bad breath. A radiograph shows a dilated esophagus. Which pressure tracing shown in the above figure was most likely taken at the lower esophageal sphincter (LES) of this patient before and after swallowing (indicated by the arrow)? The dotted line represents a pressure of 0 mm Hg. A) A B) B C) C D) D E) E
9. C) Achalasia is a condition in which the LES fails to relax during swallowing. As a result, food swallowed into the esophagus fails to pass from the esophagus into the stomach. Trace C shows a high, positive pressure that fails to decrease after swallowing, which is indicative of achalasia. Trace A shows a normal pressure tracing at the level of the LES, reflecting typical receptive relaxation in response to the food bolus. Trace E is similar to trace C, but the pressures are subatmospheric. Subatmospheric pressures occur only in the esophagus where it passes through the chest cavity.
10. The proenzyme pepsinogen is secreted mainly from which of the following structures? A) Acinar cells of the pancreas B) Ductal cells of the pancreas C) Epithelial cells of the duodenum D) Gastric glands of the stomach
10. D) Pepsinogen is the precursor of the enzyme pepsin. Pepsinogen is secreted from the peptic or chief cells of the gastric gland (also called the oxyntic gland). To be converted from the precursor form to the active form (pepsin), pepsinogen must come in contact with hydrochloric acid or pepsin itself. Pepsin is a proteolytic enzyme that digests collagen and other types of connective tissue in meats.
11. Which hormone is released by the presence of fat and protein in the small intestine and has a major effect in decreasing gastric emptying? A) CCK B) GLIP C) Gastrin D) Motilin E) Secretin
11. A) CCK is the only gastrointestinal hormone that inhibits gastric emptying under physiological conditions. This inhibition of gastric emptying keeps the stomach full for a prolonged time, which is one reason why a breakfast containing fat and protein “sticks with you” better than breakfast meals containing mostly carbohydrates. CCK also has a direct effect on the feeding centers of the brain to reduce further eating. Although CCK is the only gastrointestinal hormone that inhibits gastric emptying, all the gastrointestinal hormones with the exception of gastrin are released to some extent by the presence of fat in the intestine.
12. Compared with plasma, saliva has the highest relative concentration of which ion under basal conditions? A) Bicarbonate B) Chloride C) Potassium D) Sodium
12. C) Under basal conditions, saliva contains high concentrations of potassium and bicarbonate ions and low concentrations of sodium and chloride ions. The primary secretion of saliva by acini has an ionic composition similar to that of plasma. As the saliva flows through the ducts, sodium ions are actively reabsorbed and potassium ions are actively secreted in exchange for sodium. Because sodium is absorbed in excess, chloride ions follow the electrical gradient, causing chloride levels in saliva to decrease greatly. Bicarbonate ions are secreted by an active transport process causing an elevation of bicarbonate concentration in saliva. The net result is that, under basal conditions, sodium and chloride concentrations in saliva are about 10 percent to 15 percent of that of plasma, bicarbonate concentration is about threefold greater than that of plasma, and potassium concentration is about seven times greater than that of plasma.
13. Which of the following can inhibit gastric acid secretion?
13. F) All these factors can inhibit gastric acid secretion under normal physiological conditions. Gastric acid stimulates the release of somatostatin (a paracrine factor), which has a direct effect on the parietal cell to inhibit acid secretion, as well as an indirect effect mediated by suppression of gastrin secretion. Secretin and GLIP inhibit acid secretion through a direct action on parietal cells as well as indirectly through suppression of gastrin secretion. Enterogastrones are unidentified substances released from the duodenum and jejunum that directly inhibit acid secretion. When acid or hypertonic solutions enter the duodenum, a neurally mediated decrease in gastric acid secretion follows.
14. The gastrointestinal hormones have physiological effects that can be elicited at normal concentrations, as well as pharmacological effects that require higher than normal concentrations. What is the direct physiological effect of the various hormones on gastric acid secretion?
14. B) Gastrin stimulates gastric acid secretion, and secretin and GLIP inhibit gastric acid secretion under normal physiological conditions. It is important to differentiate the physiological effects of the gastrointestinal hormones from their pharmacological actions. For example, gastrin and CCK have identical actions on gastrointestinal function when large, pharmacological doses are administered, but they do not share any actions at normal physiological concentrations. Likewise, GLIP and secretin share multiple actions when pharmacological doses are administered, but only one action is shared at physiological concentrations: inhibition of gastric acid secretion.
15. The cephalic phase of gastric secretion accounts for about 30 percent of the acid response to a meal. Which of the following can completely eliminate the cephalic phase of gastric secretion? A) Antacids (e.g., Rolaids) B) Antigastrin antibody C) Atropine D) Histamine H2 blocker E) Vagotomy F) Sympathectomy
15. E) The cephalic phase of gastric secretion occurs before food enters the stomach. Seeing, smelling, chewing, and anticipating food is perceived by the brain, which, in essence, tells the stomach to prepare for a meal. Stimuli for the cephalic phase thus include mechanoreceptors in the mouth, chemoreceptors (smell and taste), thought of food, and hypoglycemia. Because the cephalic phase of gastric secretion is mediated entirely by way of the vagus nerve, vagotomy can abolish the response. Antacids neutralize gastric acid, but they do not inhibit gastric secretion. An antigastrin antibody would attenuate (but not abolish) the cephalic phase because this would have no effect on histamine and acetylcholine stimulation of acid secretion. Atropine would attenuate the cephalic phase by blocking acetylcholine receptors on parietal cells; however, atropine does not abolish acetylcholine stimulation of gastrin secretion. A histamine H2 blocker would attenuate the cephalic phase of gastric secretion but would not abolish it.
16. Migrating motility complexes (MMCs) occur about every 90 minutes between meals and are thought to be stimulated by the gastrointestinal hormone motilin. An absence of MMCs causes an increase in which of the following? A) Duodenal motility B) Gastric emptying C) Intestinal bacteria D) Mass movements E) Swallowing
16. C) MMCs (sometimes called interdigestive myoelectric complexes) are peristaltic waves of contraction that begin in the stomach and slowly migrate in an aboral direction along the entire small intestine to the colon. By sweeping undigested food residue from the stomach, through the small intestine, and into the colon, MMCs function to maintain low bacterial counts in the upper intestine. Bacterial overgrowth syndrome can occur when the normally low bacterial colonization in the upper gastrointestinal tract increases significantly. It should be clear that an absence of MMCs would decrease duodenal motility and gastric emptying. MMCs do not have a direct effect on mass movements and swallowing
17. Which manometric recording in the above figure illustrates normal function of the esophagus at midthoracic level before and after swallowing (indicated by the arrow)? The dotted lines represent a pressure of 0 mm Hg. A) A B) B C) C D) D E) E
17. C) Trace C shows a basal subatmospheric pressure with a positive pressure wave caused by passage of the food bolus. Trace A does not correspond to any normal event in the esophagus. Trace B could represent the LES in a patient with achalasia. Trace D depicts normal operation of the LES. Trace E show a basal positive pressure trace, which does not occur where the esophagus passes through the chest cavity
18. Gastric emptying is tightly regulated to ensure that chyme enters the duodenum at an appropriate rate. Which event promotes gastric emptying under normal physiological conditions in a healthy person?
18. C) Gastric emptying is accomplished by coordinated activities of the stomach, pylorus, and small intestine. Conditions that favor gastric emptying include (a) increased tone of the orad stomach, which helps to push chyme toward the pylorus; (b) forceful peristaltic contractions in the stomach that move chyme toward the pylorus; (c) relaxation of the pylorus; which allows chyme to pass into the duodenum; and (d) absence of segmentation contractions in the intestine, which can otherwise impede the entry of chyme into the intestine.
A tropical hurricane hits a Caribbean island, and the people living there are forced to drink unclean water. Within the next several days, a large number of people experience severe diarrhea, and about half of these people die. Samples of drinking water are positive for the bacterium Vibrio cholerae.
19. A toxin from V. cholerae is most likely to stimulate an increase in which of the following in the epithelial cells of the crypts of Lieberkühn in these people ? A) Cyclic adenosine monophosphate (cAMP) B) Cyclic guanosine monophosphate (cGMP) C) Chloride absorption D) Sodium absorption
19. A) The toxin from V. cholerae (cholera toxin) causes an irreversible increase in cAMP levels (not cGMP levels) in the enterocytes located in the crypts of Lieberkühn of the small intestine. This increase in cAMP causes an irreversible opening of chloride channels on the luminal membrane. Movement of chloride ions into the gut lumen causes a secondary movement of sodium ions to maintain electrical neutrality. Water follows the osmotic gradient created by sodium and chloride, causing a tremendous increase in fluid loss into the gut lumen. Severe diarrhea follows.
A tropical hurricane hits a Caribbean island, and the people living there are forced to drink unclean water. Within the next several days, a large number of people experience severe diarrhea, and about half of these people die. Samples of drinking water are positive for the bacterium Vibrio cholerae.
20. Which type of ion channel is most likely to be irreversibly opened in the intestinal epithelial cells of these people? A) Calcium B) Chloride C) Magnesium D) Potassium E) Sodium
20. B) Cholera toxin causes an irreversible opening of chloride channels in the enterocytes located in the crypts of Lieberkühn of the small intestine, as indicated in the explanation for the previous answer. Although sodium ions enter the gut lumen to maintain electrical neutrality after the flux of chloride ions into the gut lumen, the sodium ions move through relatively large paracellular pathways rather than through actual sodium channels. Calcium, potassium, and magnesium do not have a significant role in the course of an infection with V. cholerae.
21. Which range best describes the life span (in days) of an intestinal enterocyte infected with V. cholerae in a person who survives? A) 1 to 3 B) 3 to 6 C) 6 to 9 D) 9 to 12 E) 12 to 15
21. B) Enterocytes are derived from stem cells located in the crypts of Lieberkühn of the small intestine. They mature as they migrate upward toward the villus tip, where they are extruded into the gut lumen, becoming part of the ingesta. In humans, the entire population of epithelial cells is replaced in 3 to 6 days. Cholera also usually runs its course in 3 to 6 days. Because cholera toxin causes an irreversible opening of chloride channels in the enterocytes, it is thought that the time course of cholera is dictated by the life span of the enterocytes.
22. The gastrointestinal hormones have physiological effects that can be elicited at normal concentrations as well as pharmacological effects that require higher than normal concentrations. What is the physiological effect of the various hormones on gastric emptying?
22. E) CCK is the only gastrointestinal hormone that inhibits gastric emptying under normal physiological conditions. CCK inhibits gastric emptying by relaxing the orad stomach, which increases its compliance. When the compliance of the stomach is increased, the stomach can hold a larger volume of food without excess buildup of pressure in the lumen. None of the gastrointestinal hormones increases gastric emptying under physiological conditions; however, gastrin, secretin, and GLIP can inhibit gastric emptying when pharmacological doses are administered experimentally.
23. A healthy 12-year-old boy ingests a meal containing 20 percent fats, 50 percent carbohydrates, and 30 percent proteins. The gastric juice is most likely to have the lowest pH in this boy at which time after the meal (in hours)? A) 0.5 B) 1.0 C) 2.0 D) 3.0 E) 4.0
23. E) The figure below shows the time course of gastric pH, rate of acid secretion, and stomach volume immediately before and for 4 hours after a meal. Note that the pH of the gastric juice is lowest immediately before the meal (not an answer choice) and 4 hours after consuming the meal (the correct answer). It is a common misconception that the pH of the gastric juice is lowest (most acidic) after a meal, when acid secretion is highest.
24. CCK and gastrin share multiple effects at pharmacological concentrations. Which effects do CCK and gastrin share (or not share) at physiological concentrations?
24. A) Gastrin and CCK do not share any effects on gastrointestinal function at normal physiological conditions; however, they have identical actions on gastrointestinal function when pharmacological doses are administered. Gastrin stimulates gastric acid secretion and mucosal growth throughout the stomach and intestines under physiological conditions. CCK stimulates growth of the exocrine pancreas and inhibits gastric emptying under normal conditions. CCK also stimulates gallbladder contraction, relaxation of the sphincter of Oddi, and secretion of bicarbonate and enzymes from the exocrine pancreas.
25. Swallowing is a complex process that involves signaling between the pharynx and swallowing center in the brain stem. Which structure is critical for determining whether a bolus of food is small enough to be swallowed? A) Epiglottis B) Larynx C) Palatopharyngeal folds D) Soft palate E) Upper esophageal sphincter
25. C) The palatopharyngeal folds located on each side of the pharynx are pulled medially, forming a sagittal slit through which the bolus of food must pass. This slit performs a selective function, allowing food that has been masticated sufficiently to pass by but impeding the passage of larger objects. The soft palate is pulled upward to close the posterior nares, which prevents food from passing into the nasal cavities. The vocal cords of the larynx are strongly approximated during swallowing, and the larynx is pulled upward and anteriorly by the neck muscles. The epiglottis then swings backward over the opening of the larynx. The upper esophageal sphincter relaxes, allowing food to move from the posterior pharynx into the upper esophagus.
26. A 48-year-old woman consumes a healthy meal. At which location in the above figure are smooth muscle contractions most likely to have the highest frequency? A) A B) B C) C D) D E) E
26. A) The frequency of slow waves is fixed in various parts of the gut. The maximum frequency of smooth muscle contractions cannot exceed the slow-wave frequency. The slow-wave frequency averages about 3 per minute in the stomach, 12 per minute in the duodenum, 10 per minute in the jejunum, and 8 per minute in the ileum. Therefore, the duodenum is most likely to have the highest frequency of smooth muscle contractions.
27. The spinal cord of a 60-year-old woman is severed at T6 in an automobile accident. She devises a method to distend the rectum to initiate the rectosphincteric reflex. Rectal distention causes which of the following responses in this woman?
27. D) When feces enters the rectum, distention of the rectal wall initiates signals that spread through the myenteric plexus to initiate peristaltic waves in the descending colon, sigmoid colon, and rectum, all of which force feces toward the anus. At the same time the internal anal sphincter relaxes, allowing the feces to pass. In people with transected spinal cords, the defecation reflexes can cause automatic emptying of the bowel because the external anal sphincter is normally controlled by the conscious brain through signals transmitted in the spinal cord.
28. An 82-year-old woman with upper abdominal pain and blood in the stool has been taking nonsteroidal antiinflammatory drugs (NSAIDs) for arthritis. Endoscopy reveals patchy gastritis throughout the stomach. Biopsies were negative for Helicobacter pylori. Pentagastrin administered intravenously would lead to a less than normal increase in which of the following? A) Duodenal mucosal growth B) Gastric acid secretion C) Gastrin secretion D) Pancreatic enzyme secretion E) Pancreatic growth
28. B) The use of NSAIDs may result in NSAID-associated gastritis or peptic ulceration. Chronic gastritis, by definition, is a histopathological entity characterized by chronic inflammation of the stomach mucosa. When inflammation affects the gastric corpus, parietal cells are inhibited, leading to reduced acid secretion. Although diagnosis of chronic gastritis can only be ascertained histologically, the administration of pentagastrin should produce a less than expected increase in gastric acid secretion. Pentagastrin is a synthetic gastrin composed of the terminal four amino acids of natural gastrin plus the amino acid alanine. It has all the same physiological properties of natural gastrin. Although gastrin and pentagastrin can both stimulate growth of the duodenal mucosa, it should be clear that intravenous pentagastrin would not cause substantial growth in the context of a clinical test. In any case, chronic administration of pentagastrin would not lead to a less than expected growth of the duodenal mucosa. Pentagastrin is not expected to increase gastrin secretion, pancreatic enzyme secretion, or pancreatic growth.
29. Which substances have a physiological role in stimulating the release of hormones or stimulating nervous reflexes, which in turn can inhibit gastric acid secretion?
29. E) The presence of acid, fatty acids, and hyperosmotic solutions in the duodenum and jejunum leads to suppression of acid secretion through a variety of mechanisms. Acid stimulates the secretion of secretin from the small intestine, which in turn inhibits acid secretion from parietal cells. Acidification of the antrum and oxyntic gland area of the stomach stimulates the release of somatostatin, which in turn inhibits acid secretion by a direct action on the parietal cells and an indirect action mediated by suppression of gastrin secretion. The presence of fatty acids in the small intestine stimulates the release of GLIP, which inhibits acid secretion both directly (parietal cell inhibition) and indirectly (by decreasing gastrin secretion). Hyperosmotic solutions in the small intestine cause the release of unidentified enterogastrones, which directly inhibit acid secretion from parietal cells. Isotonic solutions have no effect on acid secretion.
30. A clinical study is conducted to determine the time course of gastric acid secretion and gastric pH in healthy volunteers after a meal consisting of 10 percent fat, 30 percent protein, and 60 percent carbohydrate. The results show an immediate increase in the pH of the gastric juice after the meal, which is followed several minutes later by a secondary increase in the rate of acid secretion. A decrease in which substance is most likely to facilitate the secondary increase in the rate of acid secretion in these volunteers? A) Gastrin B) Cholecystokinin C) Somatostatin D) Vasoactive intestinal peptide
30. C) Before a meal, when the stomach is empty, the pH of the gastric juice is at its lowest point and acid secretion is suppressed. Acid secretion is suppressed in part because (a) the concentrated hydrogen ions in the gastric juice stimulate somatostatin release, which has a direct action to decrease the secretion of both gastrin and acid, and (b) the acid itself has a direct effect to suppress parietal cell secretions. When a meal is taken, the buffering effects of the food cause the gastric pH to increase, which in turn decreases somatostatin release. Cholecystokinin and vasoactive intestinal peptide do not have a role in the regulation of gastric acid secretion.
31. Vomiting is a complex process that requires coordination of numerous components by the vomiting center located in the medulla. Which of the following occurs during the vomiting act?
31. D) The act of vomiting is preceded by antiperistalsis that may begin as far down in the gastrointestinal tract as the ileum. Distention of the upper portions of the gastrointestinal tract (especially the duodenum) becomes the exciting factor that initiates the actual act of vomiting. At the onset of vomiting, strong contractions occur in the duodenum and stomach along with partial relaxation of the lower esophageal sphincter. From then on, a specific vomiting act ensues that involves (a) a deep breath, (b) relaxation of the upper esophageal sphincter, (c) closure of the glottis, and (d) strong contractions of the abdominal muscles and diaphragm.
32. A 34-year-old woman has a recurrent history of duodenal ulcers associated with diarrhea, steatorrhea, and hypokalemia. Her fasting gastrin level is 550 pg/ml, and basal acid secretion is 18 mmol/hour. Human secretin at a dose of 0.4 μg/kg of body weight is administered intravenously over 1 minute. Postinjection blood samples are collected after 1, 2, 5, 10, and 30 minutes for determination of serum gastrin concentrations. Which serum gastrin concentration is considered diagnostic for gastrinoma in this woman (in pg/ml)? A) 450 B) 500 C) 550 D) 600 E) 700
32. E) Secretin inhibits gastrin secretion from normal G cells in the antrum and duodenum but actually stimulates gastrin secretion in gastrinoma cells. Any increase in serum gastrin concentration greater than 110 pg/ml above baseline after administration of human secretin is diagnostic of gastrinoma (also called ZollingerEllison syndrome). The secretin test is considered the most sensitive and accurate diagnostic method for gastrinoma
33. Various proteolytic enzymes are secreted in an inactive form into the lumen of the gastrointestinal tract. Which of the following substances are important for activating one or more proteolytic enzymes, converting them to an active form?
33. E) Essentially all proteolytic enzymes are secreted in an inactive form, which prevents autodigestion of the secreting organ. Enterokinase is physically attached to the brush border of the enterocytes that line the inner surface of the small intestine. Enterokinase activates trypsinogen to become trypsin in the gut lumen. The trypsin then catalyzes the formation of additional trypsin from trypsinogen, as well as several other proenzymes (e.g., chymotrypsinogen, procarboxypeptidase, proelastase). Pepsin is first secreted as pepsinogen, which has no proteolytic activity. However, as soon as it comes into contact with hydrochloric acid, and especially in contact with previously formed pepsin plus hydrochloride acid, it is activated to form pepsin.
34. A 71-year-old man with hematemesis and melena has a cresenteric ulcer in the duodenum. Lavage dislodged the clot, revealing an underlying raised blood vessel, which was successfully eradicated via cautery with a bipolar gold probe. Which of the following factors are diagnostic for duodenal ulcer?
34. B) Neither plasma gastrin levels nor the rate of acid secretion are diagnostic for duodenal ulcer. However, when patients with a duodenal ulcer are pooled together, they exhibit a statistically significant increase in the rate of acid secretion and a statistically significant decrease in plasma gastrin levels. How is this possible? The basal and maximal acid secretion rates of normal subjects range from 1 to 5 mEq/h and from 6 to 40 mEq/h, respectively, which overlaps with the basal (2- 10 mEq/h) and maximal (30-80 mEq/h) acid secretion rates of persons with a duodenal ulcer. The increase in acid secretion of the average person with a duodenal ulcer suppresses the secretion of gastrin from the antrum of the stomach. It should be obvious that endoscopy is diagnostic for duodenal ulcer.
35. A clinical study is conducted in which gastric acid secretion is stimulated using pentagastrin before and after treatment with a histamine H2 blocker. Which rates of gastric acid secretion (in mEq/hr) are most likely to have occurred in this experiment?
35. C) The various secretagogues, which include acetylcholine, gastrin, and histamine, have a multiplicative or synergistic effect on gastric acid secretion. This means that histamine potentiates the effects of gastrin and acetylcholine and that H2 blockers attenuate the secretory responses to both acetylcholine and gastrin. Likewise, acetylcholine potentiates the effects of gastrin and histamine and atropine attenuates the secretory effects of histamine and gastrin. Therefore, in the experiment described, the stimulation of acid secretion by pentagastrin is attenuated by the H2 blocker because of this multiplicative effect of the secretagogues.
36. A 23-year-old medical student consumes a cheeseburger, fries, and chocolate shake. Which of the following hormones produce physiological effects at some point during the next several hours?
36. E) All of the gastrointestinal hormones are released after a meal and all have physiological effects.
37. Which structure best describes the origin of tracing X shown in the figure? A) Distal rectum B) Ileocecal valve C) Internal anal sphincter D) LES E) Proximal rectum
37. C) The internal anal sphincter relaxes when the rectum is stretched, as indicated by repeated decreases in pressure after inflation of the rectal balloon. Pressures in the distal and proximal rectum are expected to increase after inflation of the rectal balloon. Inflation of a rectal balloon should not affect pressures at the lower esophageal sphincter or ileocecal valve.
38. Which of the following best describes the condition for which the patient received pelvic floor training? A) Anal fissure (i.e., a tear or superficial laceration) B) Chronic diarrhea C) Fecal incontinence (i.e., no control over defecation) D) Hemorrhoids E) Hirschsprung’s disease
38. C) Before pelvic floor training, the pressure at the external anal sphincter was unchanged after inflation of the rectal balloon. This failure of the external anal sphincter to contract is expected to result in defecation. After pelvic floor training, the external anal sphincter contracts when the rectal balloon is inflated, which prevents inappropriate defecation.
39. A 68-year-old woman with hematemesis has heartburn and stomach pain. An endoscopy shows inflammation involving the gastric body and antrum as well as a small gastric ulcer. Biopsies were positive for H. pylori. H. pylori damages the gastric mucosa primarily by increasing mucosal levels of which of the following? A) Ammonium B) Bile salts C) Gastrin D) NSAIDs E) Pepsin
39. A) H. pylori is a bacterium that accounts for 95 percent of patients with a duodenal ulcer and virtually 100 percent of patients with a gastric ulcer when chronic use of aspirin or other NSAIDs are eliminated. H. pylori is characterized by high urease activity, which metabolizes urea to NH3 (ammonia). Ammonia reacts with H+ to become ammonium (NH4 +). This reaction allows the bacterium to withstand the acid environment of the stomach. The ammonium production is believed to be the major cause of cytotoxicity because the ammonium directly damages epithelial cells, increasing the permeability of the gastric mucosal barrier. Bile salts and NSAIDs can also damage the gastric mucosal barrier, but these substances are not directly related to H. pylori infection. Pepsin can exacerbate the mucosal lesions cause by H. pylori infection, but pepsin levels are not increased by H. pylori. It should be clear that gastrin does not mediate the mucosal damage caused by H. pylori.
40. A physiology experiment is conducted in an isolated rat small intestine. The intestine is bathed with all essential nutrients, ions, and gases in a glass dish maintained at a temperature of 37°C. The proximal jejunum is observed to contract at a frequency of five contractions per minute. A glass micropipette is then inserted into an interstitial cell of Cajal (pacemaker cell) at the same location in the jejunum, and a slow-wave frequency of 10 contractions per minute is recorded. Norepinephrine is then added to the bathing solution. Which of the following best describes the most likely slow-wave frequency and contraction frequency after treatment with norepinephrine (in occurrences per minute)?
40. B) Slow-wave frequency is not affected significantly by either the autonomic nervous system or hormones; it is relatively constant at any given location in the small intestine. When a slow wave reaches a threshold value, a calcium spike potential (action potential) occurs and calcium ions enter the smooth muscle cell, which causes it to contract. Norepinephrine hyperpolarizes smooth muscle cells in the intestine and thereby decreases the likelihood that the membrane potential can reach a threshold value. Therefore, norepinephrine does not affect the basal slow-wave frequency of 10 occurrences per minute but does lower the contraction frequency of the smooth muscle cells to 0 occurrences per minute in this problem.
41. A healthy 21-year-old woman eats a big meal and then takes a 3-hour ride on a bus that does not have a bathroom. Twenty minutes after eating, the woman feels a strong urge to defecate, but manages to hold it. Which mechanisms have occurred in this woman?
41. E) The defecation reflex (also called the rectosphincteric reflex) occurs when a mass movement forces feces into the rectum. When the rectum is stretched, the internal anal sphincter relaxes and the rectum contracts pushing the feces toward the anus. The external anal sphincter is controlled voluntarily and can be contracted when defecation is not possible. Therefore, when a person feels the urge to defecate, the internal anal sphincter is relaxed, the rectum contracts, and the external anal sphincter is either contracted or relaxed depending on the circumstances.
42. A physiology experiment is conducted in an anesthetized rat. The distal duodenum is opened without disturbing its blood supply, and an oxygen-recording micropipette is inserted into the tip of a villus that is submerged in inert oil. An oxygen value of 10 mm Hg is recorded. The distal duodenum at the same location is then treated with the vasodilator adenosine. Which value of oxygen is most likely in the tip of the villus within 2 minutes after treatment with adenosine (in mm Hg)? A. 0 B. 5 C. 7 D. 10 E. 12
42. E) Oxygen is shunted from the artery of a villus into its venous drainage so that by the time the arterial blood reaches the villus tip, the oxygen tension has been reduced to about 10 mm Hg. Adenosine dilates the villus artery, increasing blood flow to the villus tip. This increase in blood flow decreases the residence time for blood in the artery so that greater amounts of oxygen can reach the villus tip, thus increasing the oxygen tension at the villus tip. Factors that decrease intestinal blood flow (e.g., hemorrhagic shock and a severe degree of exercise) can lead to ischemic death of villi because of their basal low level of oxygenation.
43. One of the following hormones can stimulate growth of the intestinal mucosa, and two other hormones can stimulate pancreatic growth. Which three hormones are these?
43. E) One of the most critical actions of gastrointestinal hormones is their trophic activity. Gastrin can stimulate mucosal growth throughout the gastrointestinal tract as well as growth of the exocrine pancreas. If most of the endogenous gastrin is removed by antrectomy, the gastrointestinal tract atrophies. Exogenous gastrin prevents the atrophy. Partial resection of the small intestine for tumor removal, morbid obesity, or other reasons results in hypertrophy of the remaining mucosa. The mechanism for this adaptive response is poorly understood. Both cholecystokinin and secretin stimulate growth of the exocrine pancreas. GLIP and motilin do not appear to have trophic actions on the gastrointestinal tract.
44. A 65-year-old man eats a healthy meal. Approximately 40 minutes later the ileocecal sphincter relaxes and chyme moves into the cecum. Gastric distention leads to relaxation of the ileocecal sphincter by way of which reflex? A) Enterogastric B) Gastroileal C) Gastrocolic D) Intestino-intestinal E) Rectosphincteric
44. B) Relaxation of the ileocecal sphincter occurs with or shortly after eating. This reflex has been termed the gastroileal reflex. It is not clear whether the reflex is mediated by gastrointestinal hormones (gastrin and cholecystokinin) or extrinsic autonomic nerves to the intestine. Note that the gastroileal reflex is named with the origin of the reflex first (gastro) and the target of the reflex named second (ileal). This method of naming is characteristic of all the gastrointestinal reflexes. The enterogastric reflex involves signals from the colon and small intestine that inhibit gastric motility and gastric secretion. The gastrocolic reflex causes the colon to evacuate when the stomach is stretched. The intestinointestinal reflex causes a bowel segment to relax when it is overstretched. The rectosphincteric reflex is also called the defecation reflex.
45. The gastric mucosal barrier has a physiological and an anatomical basis to prevent back-leak of hydrogen ions into the mucosa. Some factors are known to strengthen the integrity of the gastric mucosal barrier, whereas other factors can weaken the barrier. Which factors strengthen or weaken the barrier?
45. D) Damage to the gastric mucosal barrier allows hydrogen ions to back-leak into the mucosa in exchange for sodium ions. A low pH in the mucosa causes mast cells to leak histamine, which damages the vasculature, causing ischemia. The ischemic mucosa allows a greater leakage of hydrogen ions—leading to more cell injury and death—resulting in a vicious cycle. Factors that normally strengthen the gastric mucosal barrier include mucus (which impedes the influx of hydrogen ions), gastrin (which stimulates mucosal growth), certain prostaglandins (which can stimulate mucus secretion), and various growth factors that can stimulate growth of blood vessels, gastric mucosa, and other tissues. Factors that weaken the gastric mucosal barrier include H. pylori (a bacterium that produces toxic levels of ammonium), as well as aspirin, NSAIDs, ethanol, and bile salts.
46. The assimilation of fats includes (1) micelle formation, (2) secretion of chylomicrons, (3) emulsification of fat, and (4) absorption of fat by enterocytes. Which sequence best describes the correct temporal order of these events? A) 4, 3, 2, 1 B) 3, 1, 4, 2 C) 3, 4, 1, 2 D) 2, 1, 4, 3 E) 4, 2, 1, 3 F) 2, 4, 1, 3 G) 1, 2, 3, 4 H) 1, 3, 2, 4
46. B) Fat entering the small intestine is first emulsified into smaller globules by bile released from the gallbladder. Pancreatic lipase in conjunction with the co-enzyme colipase then digests the fat (which is mostly triglycerides) into monoglycerides and free fatty acids; these substances then become surrounded by bile salts to form water-soluble aggregates called micelles. When a micelle makes contact with an enterocyte of the intestinal wall, the monoglycerides and free fatty acids diffuse directly through the cell membrane into the enterocyte; triglycerides are too large to be absorbed. Once inside the enterocyte, the monoglycerides and free fatty acids form new triglyceride molecules that are subsequently packaged by the Golgi apparatus into chylomicrons. The chylomicrons exocytose at the basolateral membrane of the enterocyte and enter a lymphatic capillary (central lacteal) in the villus.
47. A 62-year-old man with dyspepsia and a history of chronic gastric ulcer has abdominal pain. Endoscopy shows a large ulcer in the proximal gastric body. Biopsies were positive for H. pylori. Which substances are used clinically for treatment of gastric ulcers of various etiologies?
47. C) The medical treatment of gastric ulcers is aimed at restoring the balance between acid secretion and mucosal protective factors. Proton pump inhibitors are drugs that covalently bind and irreversibly inhibit the H+/K+ adenosine triphosphatase (ATPase) pump, effectively inhibiting acid release. Therapy can also be directed toward histamine release, that is, H2 blockers, such as cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), and nizatidine (Axid). These agents selectively block the H2 receptors in the parietal cells. Antibiotic therapy is used to eradicate the H. pylori infection. NSAIDs can cause damage to the gastric mucosal barrier, which is a forerunner of gastric ulcer.
48. Cystic fibrosis (CF) is an inherited disorder of the exocrine glands affecting children and young people. Mucus in the exocrine glands becomes thick and sticky and eventually blocks the ducts of these glands (especially in the pancreas, lungs, and liver), forming cysts. A primary disruption in the transfer of which ion across cell membranes occurs in CF, leading to decreased secretion of fluid? A) Calcium B) Chloride C) Phosphate D) Potassium E) Sodium
48. B) Movement of chloride ions out of cells leads to secretion of fluid by cells. CF is caused by abnormal chloride ion transport on the apical surface of epithelial cells in exocrine gland tissues. The CF transmembrane regulator (CFTR) protein functions both as a cAMPregulated Cl− channel and, as its name implies, a regulator of other ion channels. The fully processed form of CFTR is found in the plasma membrane of normal epithelia. Absence of CFTR at appropriate cellular sites is often part of the pathophysiology of CF. However, other mutations in the CF gene produce CFTR proteins that are fully processed but are nonfunctional or only partially functional at the appropriate cellular sites.
49. A 45-year-old man presents with abdominal pain and hematemesis. An abdominal examination was relatively benign, and abdominal radiographs were suggestive of a perforated viscus. Endoscopy revealed a chronically perforated gastric ulcer, through which the liver was visible. Which mechanism is a forerunner to gastric ulcer formation? A) Back-leak of hydrogen ions B) Mucus secretion C) Proton pump inhibition D) Tight junctions between cells E) Vagotomy
49. A) Hydrogen ions leak into the mucosa when it is damaged. As the hydrogen ions accumulate in the mucosa, the intracellular buffers become saturated, and the pH of the cells decreases, resulting in injury and cell death. The hydrogen ions also damage mast cells, causing them to secrete excess amounts of histamine. The histamine exacerbates the condition by damaging blood capillaries within the mucosa. The result is focal ischemia, hypoxia, and vascular stasis. The mucosal lesion is a forerunner of gastric ulcer. Mucus secretion helps strengthen the gastric mucosal barrier because mucus impedes the leakage of hydrogen ions into the mucosa. Various proton pump inhibitors are used as a treatment modality for gastric ulcers because these inhibitors can decrease the secretion of hydrogen ions (protons). The tight junctions between cells within the mucosa help prevent the back-leak of hydrogen ions. Vagotomy was once used to treat gastric ulcer disease because severing or crushing the vagus nerve decreases gastric acid secretion.
50. A 10-year-old boy consumes a glass of milk and two cookies. His LES and fundus relax while the food is still in the esophagus. Which substance is most likely to cause relaxation of the LES and fundus in this boy? A. Gastrin B. Histamine C. Motilin D. Nitric oxide E. Norepinephrine
50. D) The fundus of the stomach and lower esophageal sphincter both relax during a swallow while the bolus of food is still higher in the esophagus. This phenomenon is called receptive relaxation. Receptive relaxation is mediated by afferent and efferent pathways in the vagus nerves. Nitric oxide is the neurotransmitter thought to mediate receptive relaxation at the smooth muscle cell. Motilin is a gastrointestinal hormone that mediates migrating motility complexes (also called housekeeping contractions); these contractions occur between meals. Gastrin and histamine do not have significant effects on smooth muscle contraction or relaxation at physiological levels. Norepinephrine can decrease smooth muscle contraction in the small intestine but is not involved in receptive relaxation.
51. A 19-year-old man is fed intravenously for several weeks after a severe automobile accident. The intravenous feeding leads to atrophy of the gastrointestinal mucosa, most likely because the blood level of which of the following hormones is reduced? A) Cholecystokinin only B) Gastrin only C) Secretin only D) Gastrin and cholecystokinin E) Gastrin and secretin F) Secretin and cholecystokinin
51. B) Gastrin has a critical role in stimulating mucosal growth throughout the gastrointestinal system.
52. Mass movements are often stimulated after a meal by distention of the stomach (gastrocolic reflex) and distention of the duodenum (duodenocolic reflex). Mass movements often lead to which of the following? A) Bowel movements B) Gastric movements C) Haustrations D) Esophageal contractions E) Pharyngeal peristalsis
52. A) Mass movements force feces into the rectum. When the walls of the rectum are stretched by the feces, the defecation reflex is initiated and a bowel movement follows when this is convenient. Mass movements do not affect gastric motility. Haustrations are bulges in the large intestine caused by contraction of adjacent circular and longitudinal smooth muscle. It should be clear that mass movements in the colon do not affect esophageal contractions or pharyngeal peristalsis.
53. A 45-year-old woman with type 1 diabetes has an early feeling of fullness when eating. She is often nauseous after a meal and vomits about once each week after eating. Glucose-induced damage to which structure is most likely to explain her gastrointestinal problem? A) Celiac ganglia B) Enteric nervous system C) Esophagus D) Stomach E) Vagus nerve
53. E) This woman has gastroparesis (also called delayed gastric emptying). This disorder slows or at times even stops the movement of chyme from the stomach to the duodenum. Diabetes is the most common known cause of gastroparesis; it occurs in about 20 percent of persons with type 1 diabetes. The high blood glucose is thought to damage the vagus nerve and thereby delay gastric emptying.
54. Which stimulus-mediator pair normally inhibits gastrin release?
54. C) Acid acts directly on somatostatin cells to stimulate the release of somatostatin. The somatostatin decreases acid secretion by directly inhibiting the acid-secreting parietal cells and indirectly by inhibiting gastrin secretion from G cells in the antrum. Acid is a weak stimulus for CCK release, but CCK does not inhibit (or stimulate) gastrin release. Acid does not stimulate GLIP release. Fatty acids are a weak stimulus for motilin, but motilin does not affect gastrin release. Fatty acids are not thought to stimulate somatostatin release.
55. A 55-year-old man consumes a meal consisting of 20 percent fat, 50 percent carbohydrate, and 30 percent protein. The following gastrointestinal hormones are released at various times during the next 6 hours: gastrin, secretin, motilin, glucose-dependent insulinotropic peptide, and cholecystokinin. Which structure is most likely to release all five hormones in this man? A) Antrum B) Colon C) Duodenum D) Esophagus E) Ileum
55. C) All five gastrointestinal hormones are released from both the duodenum and jejunum. Only gastrin is released from the antrum. Small amounts of cholecystokinin and secretin are also released from the ileum. No gastrointestinal hormones are released from the colon or esophagus
56. An 89-year-old man has a cerebrovascular accident (stroke) in the medulla and pons that completely eliminates all vagal output to the gastrointestinal tract. Which function is most likely to be totally eliminated in this man? A) Gastric acid secretion B) Gastrin release C) Pancreatic bicarbonate secretion D) Primary esophageal peristalsis E) Secondary esophageal peristalsis F) None of the above
56. D) Primary peristalsis of the esophagus is a continuation of pharyngeal peristalsis; central control originates in the swallowing center located in the medulla and pons. Visceral somatic fibers in the vagus nerves directly innervate smooth muscle fibers of the pharynx and upper esophagus, which coordinate pharyngeal peristalsis and primary peristalsis of the esophagus. Esophageal contractions can occur independently of vagal stimulation by a local stretch reflex initiated by the food bolus itself; this phenomenon is called secondary peristalsis. Although the vagus nerves can stimulate gastric acid secretion, gastrin release, and pancreatic bicarbonate secretion, these processes can be activated by other mechanisms. Thus, elimination of vagal stimulation does not completely eliminate them.
57. An 84-year-old man with hematemesis and melena is diagnosed with a duodenal ulcer. A patient diagnosed with a duodenal ulcer is likely to exhibit which of the following?
57. D) Persons with duodenal ulcers have about 2 billion parietal cells and can secrete about 40 mEq H+ per hour. Unaffected individuals have about 50 percent of these values. Plasma gastrin levels are related inversely to acid secretory capacity because of a feedback mechanism by which antral acidification inhibits gastrin release. Thus, plasma gastrin levels are reduced in persons with duodenal ulcers. Maximal acid secretion and plasma gastrin levels are not diagnostic for duodenal ulcer disease because of significant overlap with the normal population among persons in each group.
58. The gastric phase of gastric secretion accounts for about 60 percent of the acid response to a meal. Which substance can virtually eliminate the secretion of acid during the gastric phase? A) Antacids (e.g., Rolaids) B) Antigastrin antibodies C) Atropine D) Histamine H2 blocker E) Proton pump inhibitor
58. C) Gastrin, acetylcholine, and histamine can directly stimulate parietal cells to secrete acid. These three secretagogues also have a multiplicative effect on acid secretion such that inhibition of one secretagogue reduces the effectiveness of the remaining two secretagogues. Acetylcholine also has an indirect effect to increase acid secretion by stimulating gastrin secretion from G cells. Somatostatin inhibits acid secretion.
59. A 71-year-old man with upper abdominal pain and blood in the stool takes NSAIDs for the pain and washes it down with whiskey. Pentagastrin administration produced lower than predicted levels of gastric acid secretion. Secretion of which substance is most likely to be diminished in this patient with gastritis? A) Intrinsic factor B) Ptyalin C) Rennin D) Saliva E) Trypsin
59. A) Intrinsic factor is a glycoprotein secreted from parietal cells (i.e., acid-secreting cells in the stomach) that is necessary for absorption of vitamin B12. The patient has a diminished capacity to secrete acid because of chronic gastritis. Because acid and intrinsic factor are both secreted by parietal cells, a diminished capacity to secrete acid is usually associated with diminished capacity to secrete intrinsic factor. Ptyalin, also known as salivary amylase, is an enzyme that begins carbohydrate digestion in the mouth. The secretion of ptyalin is not affected by gastritis. Rennin, known also as chymosin, is a proteolytic enzyme synthesized by chief cells in the stomach. Its role in digestion is to curdle or coagulate milk in the stomach, a process of considerable importance in very young animals. It should be clear that saliva secretion is not affected by gastritis. Trypsin is a proteolytic enzyme secreted by the pancreas.
60. Gastric acid is secreted when a meal is consumed. Which factors have a direct action on the parietal cell to stimulate acid secretion?
60. E) A proton pump inhibitor such as omeprazole inhibits all acid secretion by directly inhibiting the H+, K+-ATPase (H+ pump). The parietal cell has receptors for secretagogues such as gastrin, acetylcholine, and histamine. Therefore, antigastrin antibodies, atropine, and histamine H2 blockers can reduce the secretion of acid, but none of these can completely eliminate acid secretion. Antacids neutralize gastric acid once it has entered the stomach, but they cannot inhibit acid secretion from parietal cells.
61. A 45-year-old woman adds high-fiber wheat and bran foods to her diet to reduce her serum cholesterol levels. She had avoided eating foods containing wheat or rye since she was a child because her mother said they would make her sick. The woman loses 25 pounds on her new diet but has frequent stomach cramps, gas, and diarrhea. She has also become weaker, finding it difficult to complete her morning walks. What is most likely to be increased in this woman? A) Blood hemoglobin concentration B) Carbohydrate absorption C) Fecal fat D) Protein absorption E) Serum calcium
61. C) This woman has celiac disease, also called glutensensitive enteropathy, which is a chronic disease of the digestive tract that interferes with the absorption of nutrients from food. Mucosal lesions seen on upper gastrointestinal biopsy specimens are the result of an abnormal, genetically determined, cell-mediated immune response to gliadin, a constituent of the gluten found in wheat; a similar response occurs to comparable proteins found in rye and barley. Gluten is not found in oats, rice, or corn. When persons with celiac disease ingest gluten, the mucosa of their small intestine is damaged by an immunologically mediated inflammatory response, which results in malabsorption and maldigestion at the brush border. Digestion of fat is normal in persons with celiac disease because lipase secreted by the pancreas still functions normally. Malabsorption in celiac disease increases the stool content of carbohydrates, fat, and nitrogen. There is no cure for celiac disease, but a strict gluten-free diet can help manage symptoms and promote intestinal healing.
62. The control of gastric acid secretion in response to a meal involves several events that take place over a 4- or 5-hour period after the meal. These events include (1) a decrease in the pH of the gastric contents, (2) an increase in the rate of acid secretion, (3) a decrease in the rate of acid secretion, and (4) an increase in the pH of the gastric contents. Which sequence best describes the correct temporal order of events over a 4- or 5-hour period after a meal? A) 4, 3, 2, 1 B) 3, 1, 4, 2 C) 3, 4, 1, 2 D) 2, 1, 4, 3 E) 4, 2, 1, 3 F) 1, 2, 3, 4 G) 2, 3, 1, 4 H) 1, 3, 2, 4
62. E) After a meal, the pH of the gastric contents increases because the food buffers the acid in the stomach. This increase in pH suppresses the release of somatostatin from delta cells in the stomach (hydrogen ions stimulate the release of somatostatin). Because somatostatin inhibits secretion of both gastrin and gastric acid, the fall in somatostatin levels leads to an increase in acid secretion. The increase in acid secretion causes the pH of the gastric contents to decrease. As the pH of the gastric contents decreases, the rate of acid secretion also decreases.
63. A newborn boy does not pass meconium within 48 hours of delivery. His abdomen is distended, and he begins vomiting. A suction biopsy of a distally narrowed segment of the colon shows a lack of ganglionic nerve cells. This newborn is at risk for developing which condition? A) Achalasia B) Enterocolitis C) Halitosis D) Pancreatitis E) Peptic ulcer
63. B) This infant has Hirschsprung’s disease, which is characterized by a congenital absence of ganglion cells in the distal colon resulting in a functional obstruction. Prolonged fecal stasis can lead to enterocolitis (i.e., inflammation of the colon); full-thickness necrosis and perforation can occur in severe cases. In achalasia, the LES fails to relax during swallowing. Halitosis (bad breath) can occur in persons with Hirschsprung’s disease, but this condition is not serious. Peptic ulcer and pancreatitis (inflammation of the pancreas) are not common in persons with Hirschsprung’s disease.
64. A 43-year-old obese woman with a history of gallstones is admitted to the emergency department because of excruciating pain in the upper right quadrant. The woman is jaundiced, and a radiograph suggests obstruction of the common bile duct. Which values of direct and indirect bilirubin are most likely to be present in the plasma of this woman (in milligrams per deciliter)?
64. C) Pancreatitis is inflammation of the pancreas. The pancreas secretes digestive enzymes into the small intestine that are essential in the digestion of fats, proteins, and carbohydrates. Reduced secretion of fluid into the pancreatic ducts in CF cause these digestive enzymes to accumulate in the ducts. The digestive enzymes then become activated in the pancreatic ducts (which typically would not occur) and can begin to “digest” the pancreas, leading to inflammation and a myriad of other problems (cysts and internal bleeding). Enterokinase is located at the brush border of intestinal enterocytes where it normally activates trypsin from its precursor, trypsinogen. Trypsin inhibitor is normally present in the pancreatic ducts where it prevents trypsin from being activated, and thus prevents autodigestion of the pancreas. When the ducts are blocked in cystic fibrosis, the available trypsin inhibitor is insufficient to prevent trypsin from being activated. Excessive secretion of CCK does not occur in persons with CF. Gallstone obstruction can lead to pancreatitis (by autodigestion) when the obstruction prevents pancreatic juice from entering the intestine, but this is unrelated to CF.
65. Which mechanism for transport of substances across the luminal cell membrane of an enterocyte is present in newborns and infants but not in adults? A) Endocytosis B) Facilitated diffusion C) Passive diffusion D) Primary active transport E) Secondary active transport
65. A) Intestinal absorption of immunoglobulins (present in colostrum) during early infancy occurs by endocytosis. This ability to absorb large molecules by endocytosis occurs during the first several months of life but does not occur thereafter. Facilitated diffusion, passive diffusion, and primary and secondary active transport are all normal transport processes in enterocytes.
66. Damage to the gastric mucosal barrier is a forerunner of a gastric ulcer. Which substance can both damage the gastric mucosal barrier and stimulate gastric acid secretion? A) Bile salts B) Epidermal growth factor C) Gastrin D) H. pylori E) Mucus
66. D) The discovery of H. pylori and its association with peptic ulcer disease, adenocarcinoma, gastric lymphoma, and other diseases make it one of the most significant medical discoveries of this century. In the United States about 26 million people will experience ulcer disease in their lifetime, and in up to 90 percent, it will likely be due to H. pylori. H. pylori is a gram-negative bacterium with high urease activity, an enzyme that catalyzes the formation of ammonia from urea. The ammonia (NH3) is converted to ammonium (NH4 +) in the acid environment of the stomach. The ammonium damages the gastric mucosal barrier because it damages epithelial cells. H. pylori also increases gastric acid secretion, possibly by increasing parietal cell mass. This combination of increased acid secretion along with damage to the gastric mucosal barrier promotes the development of gastric ulcer. Bile salts can damage the gastric mucosal barrier, but they do not have a clinically significant effect on acid secretion. Epidermal growth factor, gastrin, and mucus strengthen the gastric mucosal barrier
67. CF is the most common cause of pancreatitis in children. Which option best explains the mechanism of CF-induced pancreatitis? A) Activation of enterokinase B) Activation of trypsin inhibitor C) Autodigestion of pancreas D) Excessive secretion of CCK E) Gallstone obstruction
67. C) About 20 percent of persons older than 65 years have gallstones (cholelithiasis) in the United States, and 1 million newly diagnosed cases of gallstones are reported each year. Gallstones are the most common cause of biliary obstruction. Regardless of the cause of gallstones, serum bilirubin values (especially direct or conjugated) are usually elevated. Indirect or unconjugated bilirubin values are usually normal or only slightly elevated. Only answer C shows a high level of direct bilirubin (conjugated bilirubin) compared with the level of indirect bilirubin (unconjugated bilirubin).