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
Vitamin B12 is absorbed in - 
Select and explain. 
A. Duodenum, B. Jejunum, C. Ileum, D. Colon
C: Ileum
Answer: C: Ileum 
Explanation: Ans. is 'c' i.e., Ileumo Vitamin B12 (cyanocobalamine) is absorbed in the ileum. 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 B12o 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.