What is required for the absorption of vitamin B12 in the intestine?

The absorption of vitamin B12 in the intestine is critically dependent on intrinsic factor, a glycoprotein produced by the stomach's parietal cells. When vitamin B12 is ingested, it binds to a protein called haptocorrin in the gastric environment. Subsequent to this binding, intrinsic factor is necessary for the absorption of vitamin B12 in the small intestine. In particular, intrinsic factor binds to the vitamin B12-haptocorrin complex once it reaches the duodenum, facilitating the absorption of vitamin B12 through specific receptors on the surface of the intestinal cells.

Without intrinsic factor, vitamin B12 cannot be adequately absorbed, leading to potential deficiencies and related health issues such as pernicious anemia. This role of intrinsic factor illustrates the importance of this protein in ensuring that vitamin B12, which is essential for many bodily functions including red blood cell formation and neurological function, is properly assimilated into the body.

The other options provided do not have a direct role in the absorption of vitamin B12. While pepsin is involved in protein digestion in the stomach, it does not interact with vitamin B12 during absorption. Cholecystokinin plays a role in digestive processes by stimulating the secretion of digestive enzymes and