Where does most nutrient absorption occur?

Correct Answer: B

Rationale: The correct answer is B: Small intestine. The small intestine is where most nutrient absorption occurs due to its large surface area, specialized villi, and microvilli that increase absorption efficiency. Digestive enzymes and bile are also secreted here to further break down nutrients. Stomach (A) primarily aids in digestion, not absorption. Large intestine (C) mainly absorbs water and electrolytes, not nutrients. Mouth (D) begins the digestion process by mechanical breakdown and some enzyme release, but minimal absorption occurs here.

Correct Answer: D

Rationale: The correct answer is D because secretin is a hormone that stimulates the secretion of bicarbonate by pancreatic duct cells. This helps neutralize the acidic chyme entering the duodenum from the stomach. A is incorrect because secretin does not directly affect salivary secretion. B is incorrect because secretin does not relax the esophageal sphincters. C is incorrect because secretin inhibits gastric secretion rather than stimulating it. Therefore, the correct choice is D as it aligns with the physiological role of secretin in pancreatic bicarbonate secretion.

Correct Answer: C

Rationale: Rationale: 1. The mucosal cells of the colon absorb Na to maintain electrolyte balance. 2. Na absorption is crucial for water reabsorption. 3. This process helps regulate stool consistency and prevent dehydration. Summary: A: Incorrect - Bile acid conversion primarily occurs in the liver. B: Incorrect - Bilirubin breakdown mainly occurs in the liver and intestines. D: Incorrect - Aromatic amino acid absorption occurs mainly in the small intestine.

Correct Answer: A

Rationale: The occult fecal blood test detects hidden blood in the stool, which can be an early sign of colonic carcinoma. This test is not specific for malabsorption syndrome, making option B incorrect. Option C is incorrect because the test is primarily used for detecting colonic carcinoma. Option D is incorrect as the test can aid in the discovery of colonic carcinoma.

Correct Answer: A

Rationale: The correct answer is A because secretin hormone is released in response to acidic gastric juice, acting to neutralize the acidity by stimulating pancreatic bicarbonate secretion. Choice B and C are incorrect as secretin does not stimulate stomach mobility or HCL secretion. Therefore, the correct answer is A as it aligns with the function of secretin in regulating pH balance in the digestive system.