Which part of the small intestine is associated with absorption of vitamin B12 and bile salts?

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

Answer: (C)

Absorption of vitamin B12 and bile salts happens in the ileum, especially the distal/terminal portion. Vitamin B12 requires intrinsic factor to be taken up by ileal enterocytes; the IF–B12 complex binds receptors on these cells and is internalized, allowing B12 to enter the bloodstream bound to transcobalamin II. Bile acids released into the small intestine are reabsorbed primarily in the terminal ileum via the apical sodium-dependent bile acid transporter, feeding back into the liver through enterohepatic circulation. If the ileum is damaged or diseased, both B12 absorption and bile acid reabsorption can be impaired. The other small intestinal regions handle different absorptive tasks, so the ileum is the main site for these two substances.