Intrinsic factor and its function?

• A. A protein that binds iron in plasma
• B. A protein that absorbs vitamin B12 and is produced in the stomach
• C. A digestive enzyme
• D. A hormone that increases calcium absorption

Answer: (B)

Intrinsic factor is a glycoprotein secreted by the stomach's parietal cells. Its job is to bind vitamin B12 in the stomach, forming a complex that travels to the terminal ileum where special receptors take it up into enterocytes for absorption. This process is essential for preventing pernicious anemia, since B12 is necessary for red blood cell production and nervous system function. Intrinsic factor is not a digestive enzyme and not a hormone, and it does not bind iron. The fact that it’s produced in the stomach and binds B12 explains why the best description is a protein produced in the stomach that binds vitamin B12 and facilitates its absorption.