The actions of secretin include:

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: 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.

Correct Answer: D

Rationale: Correct Answer: D Rationale: 1. Chemotrypsinogen is the inactive precursor of chymotrypsin. 2. Trypsin activates chemotrypsinogen to form active chymotrypsin. 3. This activation occurs in the small intestine, enabling protein digestion. Summary: A: Trypsin is secreted as an inactive zymogen, not in the active form. B: CCK stimulates enzyme secretion, not bicarbonate. C: Secretin mainly stimulates bicarbonate secretion, not enzymes.

Correct Answer: D

Rationale: The correct answer is D: Colon. The colon has the longitudinal muscle of the muscularis arranged into distinct longitudinal bundles called taeniae coli. This unique structure helps in the formation of haustra, the pouches seen in the colon. In contrast, the duodenum, jejunum, and ileum do not have this specific arrangement of longitudinal muscle bundles. The duodenum has a smooth muscle layer, while the jejunum and ileum have a continuous layer of smooth muscle without distinct longitudinal bundles. Therefore, the colon is the region of the GI tract where the longitudinal muscle is organized into distinct bundles.