This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T., Subject name: Physiology
Parietal cells in the stomach secrete a protein crucial for the absorption of vitamin B12 by the ileum. What is this protein? 
Select and explain. 
A. Intrinsic factor, B. Gastrin, C. Somatostatin, D. Cholecystokinin (CCK)
A: Intrinsic factor
Answer: A: Intrinsic factor 
Explanation: Ans. A. Intrinsic factorIntrinsic factor is critical for the absorption of vitamin B12 by the ileum. None of the other substances is secreted by parietal cells. Gastrin, somatostatin, and CCK are secreted by specialized GI endocrine cells, whereas chylomicrons are produced by enterocytes