This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Digestion and Absorption, Subject name: Physiology
Intrinsic factor is required for absorption of - 
Select and explain. 
A. Folic acid, B. Vitamin B12, C. Vitamin B2, D. Vitamin B6
B: Vitamin B12
Answer: B: Vitamin B12 
Explanation: Ans. is 'b' i.e., Vitamin B12 o Vitamin B12 (cyanocobalamine) is absorbed in the ileum, o Intrinsic factor (of castle) is necessary for its absorption. o IF is secreted by oxyntic cells of stomach. In the lumen of the small intestine, IF forms a complex with vitamin B12. o Vitamin B12-IF complex binds with a specific receptor on the surface of the epithelial cells of the ileum. o Vitamin B12 is transported into the enterocytes leaving behing IF at the brush border.