Which vitamin requires intrinsic factor for absorption, and where does absorption occur?

Which vitamin requires intrinsic factor for absorption, and where does absorption occur?

• A. Vitamin B2; absorption occurs in the jejunum.
• B. Vitamin B6; absorption occurs in the ileum.
• C. Vitamin B12; absorption occurs in the ileum.
• D. Vitamin B9; absorption occurs in the duodenum.

Answer: (C)

Vitamin B12 needs intrinsic factor to be absorbed, and this process happens in the ileum. Intrinsic factor is a protein made by stomach parietal cells that binds B12 in the gut, protecting it and allowing it to be taken up by specific receptors on ileal enterocytes through receptor-mediated endocytosis. Once inside the cell, B12 is released and then travels in the blood bound to transcobalamin II to the liver and other tissues. This special requirement explains why B12 absorption is impaired when intrinsic factor is missing or deficient, such as in pernicious anemia or after certain stomach surgeries. Other vitamins listed don’t depend on intrinsic factor for absorption. Riboflavin is absorbed in the proximal small intestine, mainly the jejunum. Vitamin B6 is also absorbed in the jejunum. Folate is absorbed in the upper small intestine, particularly the duodenum and jejunum, and does not require intrinsic factor for its uptake.

Vitamin B12 needs intrinsic factor to be absorbed, and this process happens in the ileum. Intrinsic factor is a protein made by stomach parietal cells that binds B12 in the gut, protecting it and allowing it to be taken up by specific receptors on ileal enterocytes through receptor-mediated endocytosis. Once inside the cell, B12 is released and then travels in the blood bound to transcobalamin II to the liver and other tissues. This special requirement explains why B12 absorption is impaired when intrinsic factor is missing or deficient, such as in pernicious anemia or after certain stomach surgeries.

Other vitamins listed don’t depend on intrinsic factor for absorption. Riboflavin is absorbed in the proximal small intestine, mainly the jejunum. Vitamin B6 is also absorbed in the jejunum. Folate is absorbed in the upper small intestine, particularly the duodenum and jejunum, and does not require intrinsic factor for its uptake.