Understanding the Role of the Terminal Ileum in Vitamin B12 Absorption and Transport

What happens to intrinsic factor exactly at the terminal ileum, where B12 is absorbed?

Intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. Its main function is to bind to vitamin B12 (also known as cobalamin) in the stomach, forming a complex that enables the absorption of B12 later on in the small intestine.

The terminal ileum, which is the final part of the small intestine, plays a crucial role in the absorption of vitamin B12. At this location, the intrinsic factor-B12 complex is recognized by specific receptors on the surface of the cells lining the intestinal wall. These receptors allow the complex to be absorbed into the cells through a process called receptor-mediated endocytosis.

Once inside the cells of the terminal ileum, the intrinsic factor-B12 complex is incorporated into small vesicles called endosomes. These endosomes then transport the complex to the basement membrane of the cells, where they fuse with lysosomes. Lysosomes contain specialized enzymes, such as proteases and cobalamin reductases, which are responsible for releasing B12 from the intrinsic factor and allowing it to be absorbed into the cells.

In the cytoplasm of the cells, vitamin B12 becomes bound to transport proteins, such as transcobalamin II, which protect it from degradation. The B12 is then released into the bloodstream and transported to various tissues where it can be utilized for important functions such as DNA synthesis, red blood cell production, and proper nervous system function.

In summary, at the terminal ileum, intrinsic factor-B12 complexes bind to specific receptors on the cells lining the intestinal wall. They are absorbed into the cells through receptor-mediated endocytosis. Inside the cells, B12 is released from intrinsic factor in the lysosomes and then bound to transport proteins for distribution throughout the body.

More Answers: