This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal System, Subject name: Physiology
Calcium is absorbed from: 
Select and explain. 
A. Duodenum, B. Jejunum, C. Ileum, D. Colon
A: Duodenum
Answer: A: Duodenum 
Explanation: All the divalent cations, except Mg++ , are absorbed from duodenum. Mg++ is absorbed from ileum. Calcium is absorbed mainly in duodenum and upper jejunum, not whole of jejunum.