Given the task definition and input, reply with output. Given a text passage, come up with an appropriate title for it. The title should accurately represent what the main focus of the passage is. The title of a passage may be present in the first few sentences of the passage and/or be referred to multiple times in the passage. The title should be 1-5 words long.

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 ileum of the small intestine . In humans , the gastric intrinsic factor protein is encoded by the GIF gene .
Intrinsic factor