The jejunum is the main site for absorption of the following except:

Correct Answer: D

Rationale: The correct answer is D, bile salts. The jejunum is primarily responsible for the absorption of nutrients like glucose, amino acids, and fatty acids. Bile salts are mainly absorbed in the ileum, the part of the small intestine that follows the jejunum. Bile salts aid in the digestion and absorption of fats, but they are not absorbed in the jejunum. Therefore, the jejunum is not the main site for absorption of bile salts. This makes option D the correct answer.

Correct Answer: D

Rationale: The correct answer is D: Bicarbonate ions. Acinar cells in the exocrine pancreas are responsible for secreting digestive enzymes, which are stimulated by secretin, CCK, and parasympathetic stimulation. Bicarbonate ions, on the other hand, are secreted by ductal cells in the pancreas to neutralize the acidic chyme entering the small intestine. Therefore, an increase in bicarbonate ions would not directly affect the secretion of acinar cells. Secretin stimulates the release of bicarbonate ions, while CCK and parasympathetic stimulation trigger the release of digestive enzymes. So, choice D is the correct answer because it does not directly increase the secretion of acinar cells within the exocrine pancreas.

Correct Answer: B

Rationale: The correct answer is B: lower gastrointestinal bleeding. Hematochezia refers to the passage of bright red blood in the stool, typically originating from the lower gastrointestinal tract. Upper gastrointestinal bleeding would present as melena (dark, tarry stool). Choice A is incorrect as hematochezia does not indicate upper GI bleeding. Choice C is incorrect because hematochezia specifically points to lower GI bleeding. Choice D is incorrect as hematochezia is associated with lower GI bleeding.

Correct Answer: B

Rationale: The correct answer is B: it is the function of parietal cells of the stomach. Parietal cells secrete hydrochloric acid in the stomach to aid in digestion. Chief cells are responsible for producing pepsinogen, not acid. Gastrin secretion actually stimulates acid secretion rather than inhibiting it, making choice C incorrect. Acetylcholine (Ach) also stimulates acid secretion, so choice D is incorrect. Parietal cells are the primary cells responsible for acid secretion in the stomach, making choice B the correct answer.

Correct Answer: A

Rationale: Rationale for Choice A: The center of defecation (Parasympathetic and anal reflexes) is in the sacral segments. In the defecation process, the sacral segments of the spinal cord play a crucial role in coordinating the parasympathetic and anal reflexes that control bowel movements. This is supported by the fact that damage to the sacral segments can lead to bowel dysfunction, such as in spinal cord injuries affecting these segments. The sacral segments are specifically responsible for regulating the relaxation of the internal anal sphincter and contraction of the rectum during defecation. Summary of Other Choices: B: Voluntary control of defecation is located in the medulla. This is incorrect as voluntary control of defecation is primarily regulated by higher brain centers, such as the cerebral cortex, and not in the medulla. C: The center for swallowing reflex is at the level of the spinal cord. This is incorrect as the center for the