Parietal cells secrete intrinsic factor which helps promote the absorption of which vitamin?

• A. Vitamin A
• B. Vitamin B12
• C. Vitamin C
• D. Vitamin D

Answer: (B)

Intrinsic factor produced by gastric parietal cells is the carrier that allows vitamin B12 to be absorbed. After B12 is released from dietary proteins in the stomach, intrinsic factor binds it to form a B12–intrinsic factor complex, which is resistant to digestion. This complex then travels to the terminal ileum, where it binds to specific receptors on enterocytes and is absorbed by receptor‑mediated endocytosis. Without intrinsic factor, B12 absorption is severely impaired, leading to pernicious anemia. The other vitamins listed do not depend on intrinsic factor: vitamins A and D are fat‑soluble and require bile and micelles for absorption, while vitamin C is water‑soluble and absorbed by transport mechanisms that do not involve intrinsic factor.