How is cobalamin absorbed in the body?

Cobalamin, also known as vitamin B12, has a unique and intricate absorption process in the body. The correct mechanism for its absorption involves the assistance of intrinsic factor, a glycoprotein produced by the parietal cells of the stomach. When cobalamin is ingested through food, it is released from proteins in the acidic environment of the stomach, then binds to intrinsic factor, forming a complex. This complex is crucial for the absorption of cobalamin because, without intrinsic factor, the vitamin cannot be adequately absorbed in the small intestine, particularly in the ileum.

Once the intrinsic factor-cobalamin complex reaches the ileum, specialized receptors facilitate the uptake of the vitamin into the enterocytes (intestinal cells). From there, cobalamin is released into the bloodstream, where it can be transported to various tissues throughout the body.

Other options address different aspects unrelated to the primary mechanism of cobalamin absorption. For instance, while absorption does occur within the intestines, simply stating that it is absorbed through the intestines does not acknowledge the essential role of intrinsic factor in this process. The liver is a site for storage of cobalamin, but it is not involved in the initial absorption after dietary intake. Likewise,