This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology and Reproduction, Subject name: Physiology
Calcium absorption is from: 
Select and explain. 
A. Proximal small intestine, B. Distal ileum, C. Middle small intestine, D. Ascending colon
A: Proximal small intestine
Answer: A: Proximal small intestine 
Explanation: Ans. (a) Proximal small intestine(Ref: Ganong, 25th ed/p.375)Active calcium absorption occurs mainly in the proximal small bowel (duodenum and proximal jejunum)