<Table> <Tr> <Td_colspan="2"> View / Edit Human </Td> <Td_colspan="2"> View / Edit Mouse </Td> </Tr> </Table> <Tr> <Td_colspan="2"> View / Edit Human </Td> <Td_colspan="2"> View / Edit Mouse </Td> </Tr> <P> 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 B12 later on in the ileum of the small intestine . In humans, the gastric intrinsic factor protein is encoded by the GIF gene . </P> <P> Haptocorrin (also known as HC, R protein, and transcobalamin I, TCN1) is another 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 . </P>

Where is b12 absorbed in the gi tract