Which essential nutrient requiring intrinsic factor is absorbed in the terminal ileum?

• A. Vitamin C
• B. Vitamin B12 (cobalamin)
• C. Vitamin D
• D. Vitamin A

Answer: (B)

Vitamin B12 (cobalamin) is the nutrient that depends on intrinsic factor for absorption, and the terminal ileum is its specific site of uptake. In the stomach, intrinsic factor produced by parietal cells binds B12 after it’s freed from dietary proteins. The B12–intrinsic factor complex then travels to the terminal ileum, where ileal enterocytes have receptors (cubilin with amnionless) that recognize this complex and internalize it via endocytosis, with calcium facilitating the uptake. Inside the enterocyte, B12 is released from intrinsic factor and bound to transcobalamin II for transport in the bloodstream. Other vitamins listed—such as vitamin C, vitamin D, and vitamin A—do not require intrinsic factor for absorption and use different digestive pathways.