Which section of the small intestine has receptors for vitamin B12 and bile salts?

• A. Duodenum
• B. Ileum
• C. Jejunum
• D. Cecum

Answer: (B)

Bile acids and vitamin B12 are reabsorbed primarily in the ileum. Vitamin B12 absorption requires binding to intrinsic factor in the stomach; the B12–intrinsic factor complex is then taken up by specialized receptors on ileal enterocytes, allowing B12 to enter the body. Bile acids, after helping digest fats, are reabsorbed in the terminal ileum via transporters, enabling enterohepatic circulation back to the liver. The duodenum and jejunum handle many nutrients but lack these specific B12–IF receptor mechanisms, and the cecum isn’t the main site for this receptor-mediated uptake or for significant bile acid reabsorption. So, the ileum is the correct section.