GI System MCAT Practice Question
A 42-year-old man presents with a 6-month history of severe epigastric pain, recurrent peptic ulcers refractory to standard PPI therapy, and chronic watery diarrhea. Upper endoscopy reveals multiple ulcers in the duodenum and gastric antrum. Laboratory studies show fasting serum gastrin level of 580 pg/mL (normal <100) and gastric pH of 1.5. CT imaging identifies a 2-cm neuroendocrine tumor in the gastric antrum. Which of the following mechanisms best explains the chronic diarrhea in this patient?
Answer choices
- AGastrin-mediated stimulation of intestinal smooth muscle motility increases transit time and prevents adequate water reabsorption
- BExcessive gastric acid denatures pancreatic enzymes and brush border disaccharidases, resulting in maldigestion and osmotic diarrheaCorrect answer
- CElevated gastrin stimulates cholecystokinin release from I cells, which inhibits intestinal sodium-coupled water absorption
- DLow duodenal pH impairs bicarbonate secretion by Brunner's glands, reducing buffering capacity and damaging the intestinal epithelium
- EGastrin directly stimulates secretory IgA production by intestinal B cells, leading to increased intestinal permeability
- FExcessive acid production increases serum cholecystokinin levels, which stimulates secretion of water and electrolytes by duodenal mucosa
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