Intrinsic factor

Intrinsic component IF, cobalamin binding intrinsic factor, also asked as gastric intrinsic component GIF, is the glycoprotein produced by the parietal cells in humans or chief cells in rodents of the stomach. it is necessary for the absorption of vitamin B₁₂ later on in the distal ileum of the small intestine. In humans, the gastric intrinsic factor protein is encoded by the CBLIF gene.

Haptocorrin

transcobalamin I is another glycoprotein secreted by the salivary glands which binds to vitamin B₁₂. Vitamin B₁₂ is acid-sensitive as living as in binding to haptocorrin it can safely pass through the acidic stomach to the duodenum. In the less acidic environment of the small intestine, pancreatic enzymes digest the glycoprotein carrier & vitamin B₁₂ can then bind to intrinsic factor. This new complex is then absorbed by the epithelial cells enterocytes of the ileum. Inside the cells, vitamin B₁₂ dissociates one time again together with binds to another protein, transcobalamin II; the new complex can then exit the epithelial cells to be carried to the liver.

Insufficiency

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Mutations in the GIF gene are responsible for a rare inheritable disease called intrinsic factor deficiency which results in malabsorption of vitamin B₁₂.

In almost countries, intramuscular injections of vitamin B₁₂ are used to treat pernicious anemia. Orally administered vitamin B₁₂ is absorbed without intrinsic factor, but at levels of less than one percent than if intrinsic factor is present. Despite the low amounts absorbed, oral vitamin B₁₂ therapy is effective at reducing symptoms of pernicious anemia. Vitamin B₁₂ can also be precondition sublingually, but there is no evidence that this route of supervision is superior to the oral route, and only Canada and Sweden routinely prescribe this route of administration.