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PHY 503: EXAM 3 PRACTICE TEST QUESTIONS WITH
ACCURATE SOLUTIONS
- The gastric phase of gastric secretion accounts for about 60% of the acid response to a meal. Which substance can virtually eliminate the secretion of acid during the gastric phase? A) antacids B) antigastrin antibodies C) atropine D) histamine H2 blocker E) proton pump inhibitor -- Correct Answer ✔✔ E) proton pump inhibitor A proton pump inhibitor such as omeprazole inhibits all acid secretion by directly inhibiting H+/K+/ATPase. The parietal cell has receptors for secretagogues such as gastrin, ACh, and histamine. Therefore antigastrin antibodies, atropine, and histamine H2 blockers can reduce secretion of acid, but none can completely eliminate acid secretion. Antacids neutralize gastric acid once it has entered the stomach, but they cannot inhibit acid secretion from parietal cells.
- Gastric acid is secreted when a meal is consumed. Which factors have a direct action on the parietal cell to stimulate acid secretion? A) gastrin B) somatostatin C) ACh D) histamine -- Correct Answer ✔✔ A, C, and D Gastrin, ACh, and histamine can directly stimulate parietal cells to secrete acid. These three secretagogues also have a multiplicative effect on acid secretion such that the inhibition of one secretagogue reduces the effectiveness of the remaining
two. ACh also has an indirect effect to increase acid secretion by stimulating gastrin secretion from G cells. Somatostatin inhibits acid secretion.
- Which of the following can inhibit gastric acid secretion? A) somatostatin B) secretin C) GLIP D) enterogastrones E) nervous reflexes F) all of the above -- Correct Answer ✔✔ F) all of the above Gastric acid stimulates the release of SST, 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 though 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, an neurally mediated decrease in gastric acid secretion follows.
- An 82 y/o woman with upper abdominal pain and blood in the stool has been taking NSAIDs for arthritis. Endoscopy reveals patchy gastritis throughout the stomach. Biopsies were negative for H. 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 -- Correct Answer ✔✔ B) gastric acid secretion NSAID use may result in NSAID-associated gastritis or peptic ulcer. 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. Administration of pentagastrin should produce a less than expected increase in gastric acid secretion. Although gastrin and pentagastrin can both stimulate growth of the duodenal mucosa, it should be clear that IV pentagastrin would not
part because the concentrated H+ in the gastric juice stimulate SST release, which has a direct action to decrease secretion of gastrin and acid. The acid itself also 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 SST release. CCK and VIP do not have a role in the regulation of gastric acid secretion.
- A 23 y/o medical student consumes a cheeseburger, fries, and a chocolate shake. Which of the following hormones produce physiological effects at some point during the next several hours? A) gastrin B) secretin C) CCK D) GLIP E) all of the above -- Correct Answer ✔✔ E) all of the above
- A 68 y/o 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 -- Correct Answer ✔✔ A) ammonium H. pylori is a bacterium that accounts for 95% of patients with a duodenal ulcer and virtually 100% of patients with a gastric ulcer when chronic use of aspirin or NSAIDs is eliminated. H. pylori is characterized by high urease activity, which metabolizes urea to ammonia. Ammonia reacts with H+ to become ammonium, which allows the bacteria to withstand the acid environment of the stomach. The ammonium directly damages the epithelial cells, increasing the permeability of the gastric mucosal barrier.
- The ileum and distal jejunum of a 34 y/o man are ruptured in an MVC. The entire ileum and part of the jejunum are resected. What is most likely to occur in this man?
A) atrophic gastritis B) constipation C) gastric ulcer D) GERD E) vitamin B12 deficiency -- Correct Answer ✔✔ E) vitamin B12 deficiency Vitamin B12 is absorbed in the ileum; this absorption requires IF, which is a glycoprotein secreted by parietal cells in the stomach. Binding of IF to dietary vitamin B12 is necessary for attachment to specific receptors in the brush border of the ileum. Atrophic gastritis is a type of autoimmune gastritis that is mainly confined to the acid-secreting 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's esophagus, which is a forerunner to adenocarcinoma.
- 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 Vibrio cholerae. A toxin from V. cholerae is most likely to stimulate an increase in which of the following in epithelial cells of the intestinal crypts of these people? A) cAMP B) cGMP C) chloride absorption D) sodium absorption -- Correct Answer ✔✔ A) cAMP The toxin from V. cholerae causes an irreversible increase in cAMP levels (not cGMP levels) in the enterocytes located in the crypts of the small intestine. This increase in cAMP causes an irreversible opening of Cl- channels on the luminal membrane. Movement of Cl- ions into the gut lumen causes a secondary movement of Na+ ions to maintain electrical neutrality. Water follows the osmotic gradient created by Na+ and Cl-, causing a tremendous increase in fluid loss into the gut lumen, and severe diarrhea follows.
proteins that are fully processed but are nonfunctional or only partially functional at the appropriate cellular sites.
- A 71 y/o male with upper abdominal pain and blood in the stool takes NSAIDs for the pain and washes them 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 -- Correct Answer ✔✔ A) intrinsic factor IF is a glycoprotein secreted from parietal cells that is necessary for absorption of B12. The patient has a diminished capacity to secrete acid because of chronic gastritis. Because acid and IF are both secreted by parietal cells, a diminished capacity to secrete acid is usually associated with a diminished capacity to secrete IF. Ptyalin, also known as salivary amylase, is an enzyme that begins CHO digestion in the mouth. Rennin, also known as chymosin, is a proteolytic enzyme synthesized by chief cells in the stomach, and its role in digestion is to curdle or coagulate milk in the stomach. It should be clear that saliva secretion is not affected by gastritis. Trypsin is a proteolytic enzyme secreted by the pancreas.
- Which ion has the highest concentration in saliva under basal conditions? A) bicarbonate B) chloride C) potassium D) sodium -- Correct Answer ✔✔ A) bicarbonate Although the potassium concentration in saliva is about 7x greater than that of plasma, and the bicarbonate concentration in saliva is only about 3x greater than that of plasma, the actual concentration of bicarbonate in saliva is 50-70 mEq/L, whereas the concentration of potassium is about 30 mEq/L under basal conditions.
- The proenzyme pepsinogen is secreted mainly from which of the following structures?
A) acinar cells from the pancreas B) ductal cells of the pancreas C) epithelial cells of the duodenum D) gastric glands of the stomach -- Correct Answer ✔✔ D) gastric glands of the stomach Pepsinogen is the precursor of the enzyme pepsin. Pepsinogen is secreted from peptic or chief cells of the gastric gland. To be converted to the active form, pepsinogen must come in contact with HCl or pepsin itself. Pepsin is a proteolytic enzyme that digests collagen and other types of connective tissue in meats.
- 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 -- Correct Answer ✔✔ A) CCK CCK is the only GI 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 containing mostly CHOs. CCK also has a direct effect on the feeding centers of the brain to reduce further eating. Although CCK is the only GI hormone that inhibits gastric emptying, all the GI hormones with the exception of gastrin are released to some extent by the presence of fat in the intestine.
- Compared with plasma, saliva has the highest relative concentration of which ion under basal conditions? A) bicarbonate B) chloride C) potassium D) sodium -- Correct Answer ✔✔ C) potassium
- Various proteolytic enzymes are secreted in an inactive form into the lumen of the GI tract. Which of the following substances are important for activating one or more proteolytic enzymes, converting them to an active form? A) trypsin B) enterokinase C) pepsin D) all of the above -- Correct Answer ✔✔ D) all of the above Essentially all proteolytic enzymes are secreted in an inactive form, which prevents autodigestion o the secreting organ. Enterokinase is physically attacked to the brush border of enterocytes that line the inner surface of the SI, and it 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 (chymotrypsinogen, procarboxypeptidase, and proelastase). Pepsin is first secreted as pepsinogen, but as soon as it comes into contact with HCl, and especially in contact with previously formed pepsin plus HCl, it is activated to form pepsin.
- The assimilation of fats includes micelle formation, secretion of chylomicrons, emulsification of fat, and absorption of fat by enterocytes. In which order do these steps occur? -- Correct Answer ✔✔ emulsification of fat, micelle formation, absorption of fat by enterocytes, secretion of chylomicrons Fat entering the SI is first emulsified into smaller globules by bile released from the gallbladder. Pancreatic lipase in conjunction with colipase then digests the fat (which is mostly TGs) into monoglycerides and FFAs. These substances then become surrounded by bile salts to form water-soluble aggregates called micelles. When a micelle makes contact with an enterocyte, the monoglycerides and FFAs diffuse directly through the cell membrane into the enterocyte; TGs are too large to be absorbed. Once inside the enterocyte, the monoglycerides and FFAs form new TG molecules that are subsequently packaged by the Golgi into chylomicrons. The chylomicrons exocytose at the basolateral membrane of the enterocyte and enter a lymphatic capillary (central lacteal) in the villus.
- The GI 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? -- Correct Answer ✔✔ gastrin stimulates, secretin inhibits, CCK has no effect, GLIP inhibits, and motilin has no effect Gastrin stimulates gastric acid secretion, and secretin and GLIP inhibit under normal physiological conditions. It is important to differentiate the physiological effects of GI hormones from their pharmacological effects. For example, gastrin and CCK have identical actions on GI function when large pharmaceutical 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 given, but only one action is shared at physiological concentration (inhibition of acid secretion).
- The GI 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 emptying? -- Correct Answer ✔✔ gastrin has no effect, secretin has no effect, CCK decreases, GLIP has no effect, and motilin has no effect CCK is the only GI 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 GI hormones increase gastric emptying under physiological conditions; however, gastrin, secretin, and GLIP can inhibit gastric emptying when pharmacological doses are given.
- CCK and gastrin share multiple effects at pharmacological concentrations. Which effects do CCK and gastrin share (or not share) at physiological concentrations? -- Correct Answer ✔✔ NOT shared: stimulation of acid secretion, inhibition of gastric emptying, stimulation of pancreatic mucosal growth, stimulation of gastric mucosal growth Gastrin and CCK do not share any effects on GI function at normal physiological concentrations. 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
- A 45 y/o male 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 H+ B) mucus secretion C) proton pump inhibition D) tight junctions between cells E) vagotomy -- Correct Answer ✔✔ A) back-leak of H+ H+ leak into the mucosa when it is damaged. As the H+ accumulates in the mucosa, the intracellular buffers become saturated, and the pH of the cells decrease, resulting in injury and cell death. The H+ also damage mast cells, causing them to secrete large amounts of histamine, which damages the blood capillaries in 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 mucosal barrier because it impedes the leakage of H+ into the mucosa. PPIs are used as a treatment for ulcers because they can decrease secretion of H+. The tight junctions between cells within the mucosa help prevent back-leak of H+. Vagotomy was once used to treat gastric ulcers, because severing the vagus nerve decreases gastric acid secretion.
- A 19 y/o man is fed intravenously for several weeks after a severe MVC. The intravenous feeding leads to atrophy of the GI mucosa, most likely because the blood level of which hormone is reduced? A) CCK only B) gastrin only C) secretin only D) gastrin and CCK E) gastrin and secretin F) secretin and CCK -- Correct Answer ✔✔ B) gastrin only Gastrin has a critical role in stimulating mucosal growth throughout the GI tract, but none of the other hormones do this.
- Which stimulus-mediator pair normally inhibits gastrin release?
A) acid-CCK B) acid-GLIP C) acid-SST D) fatty acid-motilin E) fatty acid-SST -- Correct Answer ✔✔ C) acid-SST Acid acts directly on SST cells to stimulate the release of SST. The SST decreases acid secretion by directly inhibiting the acid-secreting parietal cells and indirectly by inhibiting gastrin secretion from antral G cells. 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 stimulator of motilin, but motilin does not affect gastrin release. Fatty acids re not thought to stimulate SST release.
- A 55 y/o man consumes a meal. Over the next 6 hours, gastrin, secretin, motilin, GLIP, and CCK are released at various times. Which structure is most likely to release all five hormones in this man? A) antrum B) colon C) duodenum D) esophagus E) ileum -- Correct Answer ✔✔ C) duodenum All 5 hormones are released from the duodenum and jejunum. Only gastrin is released from the antrum. Small amounts of CCK and secretin are also released from the ileum. No GI hormones are released from the colon or esophagus.
- 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: a decrease in pH of gastric contents, an increase in rate of acid secretion, a decrease in rate of acid secretion, and an increase in the pH of the gastric contents. What is the order of these events? -- Correct Answer ✔✔ increase in pH of gastric contents, increase in rate of acid secretion, decrease in pH of gastric contents, decrease in rate of acid secretion 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 SST from
- A 43 y/o male eats a meal containing 40% protein, 10% fat, and 50% CHO. Thirty minutes later, he 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) rectosphinteric -- Correct Answer ✔✔ A) duodenocolic Appearance of mass movements after meals is facilitate by gastrocolic and duodenocolic reflexes, which result form distension of the stomach and duodenum. They are greatly suppressed when the extrinsic autonomic nerves to the colon have been removed; therefore, reflexes are likely transmitted by way of the ANS. All the gut reflexes are named with the anatomical origin of the reflex as the prefix followed by the gut segment in which the outcome is observed. 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 secretion. The intestino- intestinal reflex occurs when overdistension or injury to a bowel segment signals the bowel to relax. The rectosphinteric reflex is initiated when feces enters the rectum and stimulates the urge to defecate.
- A 23 y/o male consumes a meal containing 30% protein, 15% fat, and 55% CHO. At which location in the GI tract are bile salts most likely to be absorbed by an active transport process? A) stomach B) duodenum C) jejunum D) ileum E) colon -- Correct Answer ✔✔ D) ileum About 94% of 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 intestinal mucosa in the distal ileum.
- 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 of the following factors can explain why the oral glucose load is cleared from the blood at a faster rate compared to the intravenous glucose load? A) CCK-induced insulin release B) CCK-induced VIP release C) GLIP-induced glucagon release D) GLIP-induced insulin release E) VIP-induced GLIP release -- Correct Answer ✔✔ D) GLIP-induced insulin release GLIP is released by the presence of fat, CHO, or protein in the GI 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 IV glucose. IV 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. VIP does not stimulate GLIP release.
- A 33 y/o 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. What is the likely pattern of pressure in the LES of this patient before and after swallowing? A) normal before swallowing, decreased after swallowing B) normal before swallowing, increased after swallowing C) elevated before swallowing, still elevated at about the same pressure after swallowing D) below 0 mmHg before swallowing, further below 0 mmHg after swallowing E) below 0 mmHg before swallowing, about the same pressure after swallowing -- Correct Answer ✔✔ C) elevated before swallowing, still elevated at about the same pressure after swallowing 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 to the stomach. High, positive pressure that fails to decrease after swallowing on a manometric trace is indicative of achalasia.
forceful peristaltic contractions in the stomach that move chyme toward the pylorus 3) relaxation of the pylorus, which allows chyme to pass into the duodenum and 4) absence of segmentation contractions in the SI, which can otherwise impede entry of chyme into the intestine.
- Swallowing is a complex process that involves signaling between the pharynx and swallowing center in the brainstem. 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) UES -- Correct Answer ✔✔ C) palatopharyngeal folds The palatopharyngeal folds are located on each side of the pharynx and are pulled medially, forming a sagittal slit through which a bolus of food must pass. This slit performs a selective function, allowing food that has been chewed sufficiently to pass by but impeding the passage of larger objects. The soft palate is pulled upward to closed 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 UES relaxes, allowing food to move from the posterior pharynx into the upper esophagus.
- A 48 y/o woman consumes a healthy meal. Where in the GI tract are smooth muscle contractions most likely to have the highest frequency? A) duodenum B) jejunum C) ileum D) proximal colon E) distal colon -- Correct Answer ✔✔ A) proximal duodenum The frequency of slow waves is fixed in various parts of the gut. The maximum frequency of smooth muscle contraction 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.
- The spinal cord of a 60 y/o woman is severed at T6 in an automobile accident. She devises a method to distend the rectum to initiate the rectosphincteric reflex. Rectal distension causes which of the following responses in this woman? A) no responses B) contraction of the rectum C) contraction of EAS and rectum D) relaxation of IAS and contraction of rectum E) relaxation of IAS and contraction of EAS F) relaxation of IAS, contraction of EAS, and contraction of rectum -- Correct Answer ✔✔ D) relaxation of IAS and contraction of rectum When feces enters the rectum, distension of the rectal wall initiates signals that spread through the myenteric plexus to initiate peristaltic waves in the descending colon, sigmoid colon, and rectum, which all force feces toward the anus. At the same time the IAS relaxes, allowing the feces to pass. In people with transected spinal cords, the defecation reflexes can cause automatic emptying of the bowel because the EAS is normally controlled by the conscious brain through signals transmitted in the spinal cord.
- A healthy 21 y/o 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? A) nothing has occurred B) contraction of EAS and rectum C) relaxation of IAS and contraction of rectum D) relaxation of IAS only E) relaxation of IAS, contraction of EAS, and contraction of rectum -- Correct Answer ✔✔ E) relaxation of IAS, contraction of EAS, and contraction of rectum The defecation (rectosphincteric) reflex occurs when a mass movement forces feces into the rectum. When the rectum is stretched, the IAS releases and the rectum contracts to push feces toward the anus. The EAS is controlled
