What is "intrinsic factor"

n. a substance produced by the mucosa of the stomach and intestines that is essential for the absorption of vitamin B12; "lack of intrinsic factor can result in pernicious anemia"

Intrinsic factor (IF), also known as gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B ( cobalamin) later on in the small intestine. In humans, the gastric intrinsic factor protein is encoded by the GIF gene.

Haptocorrin (also known as HC, R protein, and transcobalamin I, TCN1), is a glycoprotein secreted by the salivary glands which binds to vitamin B Vitamin B is acid sensitive and in binding to transcobalamin I 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 and vitamin B can then bind to intrinsic factor. This new complex is then absorbed by the epithelial cells ( enterocytes) of the ileum. Inside the cells, B dissociates once again and binds to another protein, transcobalamin II (TCN2); the new complex can then exit the epithelial cells to be carried to the liver.