The jejunum is the main site for absorption of except:

Correct Answer: D

Rationale: The correct answer is D, Vitamin B12. The jejunum is not the main site for absorption of Vitamin B12; instead, it is absorbed in the terminal ileum. Glucose, amino acids, and fatty acids are primarily absorbed in the jejunum. Absorption of Vitamin B12 occurs in the ileum where it binds to intrinsic factor secreted by the stomach. Therefore, the jejunum is not the main site for absorption of Vitamin B12, making it the correct answer. Choices A, B, and C are incorrect because the jejunum is indeed the main site for absorption of glucose, amino acids, and fatty acids, respectively.

Correct Answer: C

Rationale: Congenital lesions causing vomiting in the first three days include pyloric stenosis and intestinal atresia. Pyloric stenosis typically presents with non-bilious projectile vomiting in the first few weeks of life, while intestinal atresia presents with bilious vomiting shortly after birth. Therefore, the correct answer is C, as both conditions can manifest with vomiting within the first three days of life. Choice A and B alone are incorrect because they each only represent one of the conditions, and choice D is incorrect as both conditions can present with vomiting in the specified time frame.

Correct Answer: D

Rationale: The correct answer is D: appendix. Carcinoid tumors in the appendix are considered the most benign due to their slow growth rate and low metastatic potential. The appendix is a small organ with limited blood supply, which restricts tumor growth and dissemination. Other choices (A: stomach, B: small intestine, C: rectum) have higher malignant potential due to larger size, increased blood supply, and higher likelihood of metastasis. Therefore, the appendix is the most benign location for carcinoid tumors.

Correct Answer: A

Rationale: Rationale: A) Lactase, maltase, and sucrase enzymes are secreted in the small intestine to break down lactose, maltose, and sucrose into simpler sugars for absorption. B) Glucose and amino acids absorption occurs via active transport, not simple diffusion. C) Bile pigments are not completely absorbed; they aid in fat digestion. D) Fat absorption is primarily a passive process, with some active transport involved, but it does not require a Na co-transport system.

Correct Answer: C

Rationale: Intrinsic factor is required for the absorption of Vitamin B12 in the upper ileum. It binds to Vitamin B12, allowing it to be absorbed. Vitamin D (Choice A) is absorbed in the small intestine but does not require intrinsic factor. Amino acids (Choice B) are absorbed in the small intestine but not dependent on intrinsic factor. Choice D is incorrect as intrinsic factor is specifically necessary for the absorption of Vitamin B12.