GIT Physiology (Secretions, Hormones, Motility, Absorption) MCQs

Physiology · 47 free questions with answers & explanations.

1. Secretin is released from S cells of the duodenum in response to low duodenal pH. Its primary action on the pancreas is to:
2. Vitamin B12 (cobalamin) absorption is dependent on intrinsic factor produced by which gastric cell?
3. A patient with a resected terminal ileum 60 cm in length develops fat malabsorption and megaloblastic anemia 2 years later. Which two absorptive functions are specifically lost due to this resection?
4. Secretin is released from S-cells in the duodenum. Which stimulus most potently triggers secretin release, and what is its primary physiologic action?
5. Parietal cells secrete HCl via the H⁺-K⁺-ATPase. The stimulation of acid secretion by histamine involves H2 receptors that activate Gs → adenylyl cyclase → cAMP → PKA. Which additional pathway, activated simultaneously by acetylcholine and gastrin, synergistically amplifies acid secretion?
6. Iron absorption in the duodenum from non-haem dietary sources requires reduction of Fe³⁺ to Fe²⁺. This reduction is catalysed by duodenal cytochrome b (DcytB) on the apical membrane of enterocytes. The subsequent transporter that imports Fe²⁺ into the enterocyte and is also the transporter mutated in DMT1-deficiency anaemia is:
7. Migrating motor complex (MMC) phase III ('housekeeper wave') occurs during fasting. Which hormone triggers MMC phase III and which neural structure coordinates its propagation?
8. Secretin from S cells of the duodenum is the primary stimulant of pancreatic HCO3- secretion. The mechanism by which ductal cells of the pancreas secrete HCO3- involves which transport system?
9. Which mechanism is responsible for the 'gastrocolic reflex' that produces the urge to defaecate after a meal?
10. A patient with short bowel syndrome after massive ileal resection has diarrhoea due to bile salt malabsorption. The primary mechanism is:
11. The cephalic phase of gastric acid secretion is abolished by vagotomy. Which intracellular mechanism in parietal cells mediates the muscarinic (M3) component of vagal stimulation?
12. Fat absorption requires micellar solubilization. In a patient with ileal resection (>100 cm), which fat-soluble vitamin deficiency would be clinically most important to monitor and why?
13. Cholecystokinin (CCK) is released from I cells in the duodenum in response to luminal fat and protein. CCK stimulates gallbladder contraction and relaxes the sphincter of Oddi primarily through which mechanism?
14. Intrinsic factor (IF) is essential for vitamin B12 absorption. IF is secreted by gastric parietal cells and binds B12 in the stomach. The IF-B12 complex is absorbed in the terminal ileum by specific receptors. What are these receptors and what happens to IF after endocytosis?
15. Interstitial cells of Cajal (ICC) in the GIT serve as pacemaker cells generating the basic electrical rhythm (slow waves). The ionic mechanism responsible for pacemaker depolarization in ICC is primarily based on:
16. In the stomach, parietal cells secrete HCl via the H⁺/K⁺-ATPase on the apical canalicular membrane. The electrical neutrality during acid secretion is maintained by Cl⁻ efflux through which channel, and the intracellular HCO₃⁻ generated is exported via which mechanism?
17. A patient with chronic pancreatitis has malabsorption of fat-soluble vitamins. Which vitamin absorption is uniquely impaired even in the ABSENCE of pancreatic insufficiency or bile salt deficiency, because it requires a specific gastric secretion?
18. Parietal cells secrete HCl via H⁺/K⁺-ATPase. The proton pump is activated by a rise in intracellular cAMP (histamine via H2 receptor) and Ca²⁺ (acetylcholine via M3 and gastrin via CCK-B receptors). Which intracellular signaling interaction explains why cimetidine (H2 blocker) is more effective at suppressing acid secretion than blocking acetylcholine alone?
19. Cholecystokinin (CCK) is released from I-cells of the duodenum in response to fat and protein. CCK inhibits gastric emptying primarily through which mechanism involving the enteric nervous system?
20. Vitamin B₁₂ absorption in the terminal ileum requires binding to intrinsic factor (IF). The IF–B₁₂ complex binds which specific receptor on ileal enterocytes for receptor-mediated endocytosis?
21. The migrating motor complex (MMC) in the fasting state has a cycle of approximately 90 minutes and is divided into four phases. Phase III (activity front) is primarily regulated by which peptide hormone?
22. Hepatic glucose sensing and gluconeogenesis are regulated by glucose-6-phosphatase (G6Pase). Glycogen storage disease type Ia (von Gierke disease) presents with severe fasting hypoglycemia because:
23. Fat-soluble vitamins A, D, E, and K are absorbed in micelle form in the small intestine. A patient with ileal resection of >100 cm is at MOST risk for deficiency of which vitamin, and why?
24. A patient undergoes an ileal resection for Crohn's disease. He subsequently develops fat malabsorption and vitamin B12 deficiency. The mechanism of vitamin B12 (cobalamin) malabsorption after ileal resection is:
25. GLP-1 (glucagon-like peptide-1) is secreted by intestinal L-cells in response to a meal. Its physiological effects relevant to glucose homeostasis include all EXCEPT:
26. Secretin is released from S-cells of the duodenum. Its primary physiological role in digestion is:
27. The interstitial cells of Cajal (ICC) in the GI tract function as:
28. In the cephalic phase of gastric acid secretion, the neural pathway involves:
29. Fat malabsorption (steatorrhea) in chronic pancreatitis is predominantly due to deficiency of which pancreatic enzyme, and what is the minimum residual enzyme output that typically prevents clinically significant steatorrhea?
30. A patient develops a VIPoma secreting vasoactive intestinal peptide. Which physiological mechanism explains the profuse watery diarrhea (>3 L/day) in this condition?
31. Bile acid malabsorption occurs in patients with terminal ileum resection. Beyond fat malabsorption, which specific complication arises from loss of the enterohepatic circulation of bile salts?
32. A patient undergoes total gastrectomy for gastric cancer. Three months later, she develops macrocytic anemia and peripheral neuropathy. Which of the following BEST explains the sequence of physiological events leading to this deficiency?
33. During the intestinal phase of digestion, cholecystokinin (CCK) is released. Which cells secrete CCK, and what are its three main effects on gastrointestinal function?
34. A 45-year-old man undergoes total gastrectomy for gastric carcinoma. Which of the following nutritional/physiological deficiencies will develop EARLIEST, requiring immediate supplementation?
35. Cholecystokinin (CCK) released from I cells of the duodenum and jejunum acts on the pancreas to stimulate enzyme secretion. Through which receptor and intracellular pathway does CCK exert its effect on pancreatic acinar cells?
36. A patient with a VIPoma (Verner-Morrison syndrome) presents with profuse watery diarrhoea, hypokalaemia, and achlorhydria. VIP (vasoactive intestinal peptide) mediates this via which intracellular mechanism in intestinal crypt cells?
37. After a fatty meal, which gastrointestinal hormone is primarily responsible for gallbladder contraction and pancreatic enzyme secretion, and where are the neurons/cells that release it located?
38. Secretin is released from S cells of the duodenum in response to acid. Its primary action on the pancreas is to:
39. The migrating motor complex (MMC) serves as the 'housekeeper' of the gut. Phase III of the MMC is characterised by which features?
40. A patient takes a proton pump inhibitor (PPI) and develops hypergastrinaemia. The elevated gastrin is due to:
41. Iron absorption in the duodenum is regulated by hepcidin, secreted by the liver. In iron-deficiency anaemia, serum hepcidin is LOW. The consequence of low hepcidin on intestinal iron absorption is:
42. A patient undergoing duodenal biopsy is found to have complete absence of enteroendocrine I cells. Which digestive function would be MOST impaired?
43. Hirschsprung's disease results from absence of ganglionic cells in the myenteric and submucosal plexuses of the distal colon. What is the physiological consequence of agangliosis?
44. A patient with a VIPoma (Verner-Morrison syndrome) presents with profuse watery diarrhoea, hypokalaemia, and achlorhydria (WDHA syndrome). VIP acts on intestinal epithelial cells via which mechanism to cause secretory diarrhoea?
45. Intrinsic factor (IF) is secreted by parietal cells of the stomach. In a patient post-total gastrectomy, which vitamin deficiency develops after 3–5 years, and through which ileal transporter is its IF-bound form absorbed?
46. Secretin is released from S cells of the duodenum in response to acid. Its primary action on the pancreas produces pancreatic juice with which distinctive characteristic?
47. Migrating motor complex (MMC) in the interdigestive state is initiated by the hormone motilin. Its physiological role is: