What is required for vitamin B12 absorption in the ileum?

• A. Intrinsic factor
• B. Bile salts
• C. Pancreatic enzymes
• D. Secretin

Answer: (A)

Intrinsic factor is essential for absorbing vitamin B12 in the ileum. It’s produced by stomach parietal cells and binds B12 after the vitamin is released from dietary proteins by acid and pepsin, with pancreatic enzymes helping to free B12 from its carrier. The resulting intrinsic factor–B12 complex then binds to specific receptors in the terminal ileum and is taken into enterocytes to be delivered to the blood. Without intrinsic factor, B12 cannot be efficiently absorbed in the ileum, which is why conditions like pernicious anemia occur. Bile salts don’t play a role in this uptake, secretin isn’t involved in B12 absorption, and while pancreatic enzymes help release B12 from proteins, the actual absorption step in the ileum depends on intrinsic factor.