GI Physiology Netter's Review Q's

Metabolism of lipids within the hepatocytes includes: A. formation of most lipoproteins, including very low density and low-density lipoproteins. B. net breakdown of phospholipids. C. net breakdown of cholesterol. D. formation of steroid hormones. E. none of the above.

A. formation of most lipoproteins, including very low density and low-density lipoproteins. The hepatocytes are the primary site of formation of lipoproteins, which carry fats, protein, and cholesterol to different tissues for processing and storage.

When chyme is present in the stomach and duodenum, all of the following actions occur EXCEPT: A. stimulation of intestinal buffers by gastrin. B. stimulation of hepatic bile production by vagal nerves. C. stimulation of pancreatic enzyme secretion by cholecystokinin. D. stimulation of intestinal buffer secretion by secretin. E. conversion of trypsinogen to trypsin by enterokinase.

A. stimulation of intestinal buffers by gastrin. The presence of chyme in the antrum of the stomach and the duodenum stimulates release of gastrin, which is a potent stimulator of gastric acid secretion. It does not promote buffer secretion.

Which of the following processes is NOT a mechanism by which sodium ions enter the intestinal epithelial cells from the lumenal membrane? A. Diffusion down the sodium concentration gradient B. Active transport via Na + /K + ATPase C. Co-transport with certain amino acids D. Co-transport with monosaccharides E. Exchange for H +

B. Active transport via Na + /K + ATPase Sodium enters the luminal membrane by all the mechanisms except the Na + pump (Na+/K+ ATPase), which is located on the basolateral membrane and maintains the low intracellular Na + concentrations that drive the luminal Na + transport mechanisms.

A 42-year-old woman undergoes resection and removal of the last third of her ileum because of ileal obstruction. What would be a consequence of this maneuver? A. Liver bile production would be downregulated. B. Micelles would not be formed. C. Vitamin B12 would not be absorbed. D. Bowel movements will be decreased. E. Water absorption would increase.

C. Vitamin B12 would not be absorbed. Because bile recycling and vitamin B12 absorption occur in the last section of the ileum, removing this part of the small intestine will prevent B12 absorption (and bile recycling). The increase in bile excretion will reduce water absorption (because of the osmotic nature of bile).

Slow waves constituting the basal electrical rhythm: A. are hyperpolarized by stretch, acetylcholine, and gastrin. B. occur at a consistent rate throughout the GI tract. C. are undulations in the resting membrane potential. D. are depolarized by sympathetic nerve stimulation. E. are absent in the colon.

C. are undulations in the resting membrane potential. The undulations are a result of small changes in membrane potential generated by the SIP (smooth muscle, I CC, P DGFR-α + cell) syncytium. The slow waves occur at different rates from the mid-stomach through the colon.

Parietal cell gastric acid secretion is regulated: A. directly by secretin. B. directly by peptide YY. C. directly and indirectly by the vagus nerve. D. indirectly by somatostatin. E. indirectly by gastrin.

C. directly and indirectly by the vagus nerve. Vagal afferent nerves stimulate gastric acid secretion directly at the parietal cell and indirectly by increasing gastrin-releasing peptide (and, thus, gastrin release) and inhibiting somatostatin release.

Which of the following mechanisms would delay or diminish the absorption of proteins? A. Inhibition of gastric somatostatin release B. An increase in Na + /K + ATPase activity in the basolateral membranes of the enterocytes C. Stimulation of gastric pepsinogen release D. A pH of 3 in the duodenum and jejunum E. Secretion of cholecystokinin

D. A pH of 3 in the duodenum and jejunum Efficient digestion of proteins in the small intestine depends on the pancreatic proteases, which have optimal catalytic activity near physiologic pH (pH between 7 and 8). Low luminal pH will significantly decrease catalytic activity and reduce the amount of proteins digested to constituents that can be absorbed.

Select the TRUE statement about gastric acid secretion. A. Histamine suppresses acid secretion. B. Blocking the H + /K + ATPase pump increases alkaline tide. C. Basolateral HCO 3− /Cl− exchangers decrease intracellular Cl − in parietal cells. D. Parasympathetic stimulation of acid secretion is limited to the cephalic phase of acid secretion. E. Proton pump (H + /K + ATPase) activity is the rate-limiting step in acid secretion.

E. Proton pump (H + /K + ATPase) activity is the rate-limiting step in acid secretion. Proton pump activity drives acid secretion and is the target for regulatory hormones, peptides, and nerves.

Motility and secretion through the GI tract is regulated by all of the following factors EXCEPT: A. duodenal hormones. B. chemoreceptors. C. autonomic nerves. D. enteric nerves. E. growth hormone.

E. growth hormone. Growth hormone has no apparent effect on motility or secretion in the GI tract.

What effects would intestinal villous atrophy (from celiac disease) have on liver function? A. Conversion of fructose to glucose in the glycolytic pathway would be increased. B. β-Oxidation of fatty acids would be decreased. C. Plasma protein production would be decreased. D. Urea production would be increased. E. Deamination of amino acids would not occur.

C. Plasma protein production would be decreased. Villous atrophy will reduce the surface area for absorption of nutrients as well as the brush border proteases and saccharidases that provide the final digestion of proteins and carbohydrates to forms that can be absorbed. Thus, absorption of proteins and carbohydrates would be significantly affected, and production of plasma proteins would be reduced.

Select the TRUE statement about pancreatic secretions. A. The release of pancreatic enzymes into the duodenum is primarily stimulated by gastrin. B. The release of pancreatic enzymes into the duodenum is primarily stimulated by the sympathetic nerves. C. Secretin is released in response to low duodenal pH and acts at the pancreas to stimulate the release of electrolyte buffer solution. D. Pancreatic proteases are released in active form. E. Pancreatic lipase digests all lipids.

C. Secretin is released in response to low duodenal pH and acts at the pancreas to stimulate the release of electrolyte buffer solution. Secretin is a hormone released from S cells in the duodenum and early jejunum in response to acidic chyme. The secretin binds to receptors on the pancreatic acinar cells and stimulates release of electrolyte buffers into the pancreatic duct.

A 25-year-old woman presents with recurrent episodes of abdominal pain, abdominal distension, and occasional vomiting that occur 2 hours after a meal. She usually has to miss work, and her symptoms resolve after a day or two, during which she has no bowel movements. A CT scan of the abdomen shows patchy segments of the colon that are thickened, as well as a stricture in the mid jejunum. What is the most likely diagnosis? A. Small bowel obstruction B. Crohn's disease C. Ulcerative colitis D. Celiac disease E. Irritable bowel syndrome

B. Crohn's disease While many of the disorders listed can result in her symptoms, the presentation of both thickening of the colon as well as a stricture in the jejunum is indicative of Crohn's disease, which can occur at any point along the small and large intestine.

Select the FALSE answer about the migrating myoelectric complex (MMC). A. The MMC is a series of contractions that "sweep" undigested fibers and bacteria into the colon. B. The parasympathetic nervous system controls the MMC contractions. C. In each cycle, the main contractions of the MMC occur during phase III. D. The hormone motilin stimulates phase III contractions. E. The MMC occurs during fasting and stops upon feeding.

B. The parasympathetic nervous system controls the MMC contractions. There is no evidence for involvement of the parasympathetic nervous system in the MMC.

Bile salt(s): A. hydrolyze dietary fats. B. are essential for creating micelles. C. are efficiently absorbed into the portal blood all along the small intestine. D. do not contribute to intestinal buffering of acidic chyme. E. production is not affected by loss of the terminal ileum.

B. are essential for creating micelles. Bile is amphipathic and essential for carrying the hydrophobic lipids through the unstirred water layer adjacent to the enterocytes. The ability to form micelles, with hydrophilic ends of bile oriented outward, and lipophilic ends oriented inward and associated with the lipids, allows the efficient transport of lipids to the intestinal cells.

Action potentials in the GI smooth muscle: A. occur only in the upper GI tract. B. are stimulated when the slow waves are depolarized above −40 mV. C. occur only in the lower GI tract. D. result from influx of sodium ions into the smooth muscle cells. E. are stimulated only by extrinsic nerves.

B. are stimulated when the slow waves are depolarized above −40 mV. Action (or spike) potentials in the GI tract are caused by the influx of calcium into the smooth muscle when the slow waves are depolarized above −40 mV. This mechanism is active throughout the tract, and depolarization can result from local stretch (mechanoreceptors acting on enteric nerves), extrinsic nerves, and peptides.

Bacteria in the GI tract: A. are found only in the colon. B. can modulate immune function in the GI tract. C. metabolize compounds to long-chain fatty acids. D. are all probiotic, unless antibiotics are used. E. have no trophic actions in the gut.

B. can modulate immune function in the GI tract. Gut flora provide a protective function by stimulating the development and maintenance of immune competence in the gut.

Input from vagal efferent nerves to the gastrointestinal tract stimulates all of the following EXCEPT: A. lower intestinal motility (ileum, proximal colon). B. salivation. C. the cephalic phase of gastric acid secretion. D. receptive relaxation in the stomach. E. hepatic bile production.

B. salivation. Vagal efferent nerves regulate all of the actions EXCEPT salivation, which is controlled by the facial and glossopharyngeal nerves. The vagus does participate in secondary esophageal peristalsis, in conjunction with local enteric nerves.

The absorption of vitamin B12 (cobalamin) is dependent on all of the following EXCEPT: A. the integrity of the terminal ileum. B. the concentration of B12 in the enterocytes. C. the presence of TC-1 in saliva. D. the presence of intrinsic factor in gastric juice. E. the presence of vitamin B12-intrinsic factor binding sites in the ileum.

B. the concentration of B12 in the enterocytes. Vitamin B12 is an essential nutrient and has multiple mechanisms protecting it from protease activity and facilitating entry into the intestinal cells. There is no limitation to absorption posed by intracellular B12 concentrations.

The liver performs all of the following functions EXCEPT: A. synthesis of cholesterol. B. vitamin production. C. β-oxidation of fatty acids. D. bile acid production. E. metabolism of proteins.

B. vitamin production. The liver performs all the functions noted except vitamin production. It does store a variety of important vitamins and minerals, including vitamin B12 and iron; it also hydroxylates vitamin D.

In a patient with celiac disease: A. gastric ulcerations are common. B. fibrosis decreases intestinal absorption and reduces portal blood flow. C. flattening of intestinal villi decreases enzymatic digestion and reduces the area for absorption. D. hypersecretion of mucus obstructs absorption. E. hyposecretion of mucus allows acidification of the intestinal lumen, decreasing enzymatic digestion.

C. flattening of intestinal villi decreases enzymatic digestion and reduces the area for absorption. Celiac sprue is an autoimmune reaction initiated by gluten proteins in wheat, resulting in the flattening of the villus lining and expansion of the crypts. The reduction in the upper villi severely decreases the brush border enzyme digestion of carbohydrates and proteins and reduces the surface area for absorption.

Select the TRUE statement about carbohydrate digestion. A. Digestion of carbohydrates begins in the intestines. B. Loss of the intestinal brush border has no effect on carbohydrate digestion. C. Disaccharidases are secreted into the duodenum from the crypts of Lieberkühn. D. Starch digestion is initiated by α-amylase. E. The majority of carbohydrate digestion occurs before the duodenum.

D. Starch digestion is initiated by α-amylase. Starch is the primary dietary carbohydrate, and digestion begins in the mouth with salivary α-amylase. Only around 25% of digestion occurs preduodenally; pancreatic α-amylase digests the remaining starch to malto-oligosaccharides, and then intestinal brush border saccharidases (maltase, isomaltase, sucrose, and lactase) digest oligosaccharides and disaccharides (sucrose and lactose) to monosaccharides (glucose, galactose, and fructose).

Secretions entering the lumen of the stomach include all of the following substances EXCEPT: A. hydrochloric acid. B. lipase. C. mucus. D. gastric inhibitory peptide. E. intrinsic factor.

D. gastric inhibitory peptide. Gastric inhibitory peptide is an endocrine hormone secreted from cells in the duodenum and jejunum of the small intestine. The other substances are secreted directly into the gastric lumen.

Vagal stimulation early in feeding will stimulate all of the following secretions EXCEPT: A. pepsins. B. gastrin. C. intrinsic factor. D. glucagon-like peptide-1 (GLP-1). E. hydrochloric acid.

D. glucagon-like peptide-1 (GLP-1). The vagus will stimulate secretions from the parietal cells (HCl, IF) and chief cells (pepsins) into the stomach lumen as well as stimulate gastrin release (from G cells) into the blood. GLP-1 is found mainly in the ileum and is secreted in response to nutrients in the chyme.

Obstruction of blood flow through the liver (from cirrhosis or hepatitis) will: A. have no effect on gastrointestinal digestion or absorption. B. have no effect on bile secretion. C. increase bile secretion. D. increase portal vein pressure. E. reduce hepatic blood content.

D. increase portal vein pressure. Obstruction of blood flow through the liver increases the pressure in the portal vein, which brings blood from the intestines to the liver. This eventually results in portal hypertension. The obstruction also reduces bile secretion.

In the small intestine, peristalsis: A. occurs primarily in response to the chemical composition of the chyme. B. proceeds in both forward and backward directions from the site of contraction. C. involves receptive relaxation of the muscle proximal (toward the mouth) to the bolus of chyme. D. involves contraction of the muscle proximal to the bolus of chyme. E. is dependent on parasympathetic innervation.

D. involves contraction of the muscle proximal to the bolus of chyme. Peristalsis follows the law of the intestines, where muscle is contracted proximal to the bolus and relaxed distal to the bolus, producing aboral movement of the chyme.

In the absence of extrinsic innervation to the gastrointestinal tract, A. propulsive movements would not occur in the small intestine. B. propulsive movements would occur in the small intestine, but secretion into the small intestine would be abolished. C. secretion would be abolished in the entire GI tract. D. motility and secretion throughout the tract would be stimulated by local mechanoreceptors, chemoreceptors, and osmoreceptors as well as hormones. E. motility and secretion would be affected only in the large intestine.

D. motility and secretion throughout the tract would be stimulated by local mechanoreceptors, chemoreceptors, and osmoreceptors as well as hormones. The GI tract has an intrinsic nervous system (enteric nerves), which responds to signals from luminal receptors and hormones as well as extrinsic nerves. When the extrinsic nerve input is severed, motility and secretion continue, but not as efficiently.

All of the following are functions of the GI tract EXCEPT: A. secretion of endocrine hormones. B. secretion of digestive enzymes. C. absorption of nutrients from chyme. D. regulation of systemic blood flow. E. storage of chyme.

D. regulation of systemic blood flow. The GI tract does not directly regulate systemic blood flow.