High Quality Content by WIKIPEDIA articles! 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 terminal ileum. In humans, the gastric intrinsic factor protein is encoded by the GIF gene. Upon entry into the stomach, vitamin B12 becomes bound to haptocorrin (R factor), a glycoprotein. The resulting complex enters the duodenum, where pancreatic enzymes digest haptocorrin. In the less acidic environment of the small intestine, B12 can then bind to intrinsic factor. This new complex travels to the ileum, where special epithelial cells endocytose them. Inside the cell, B12 dissociates once again and binds to another protein, transcobalamin II. The new complex can exit the epithelial cells to enter the liver.