This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Physiology
Parathormone (Parathyroid hormone/PTH) increase calcium levels and reduces phosphate level by acting on 
Select and explain. 
A. Proximal tubules, B. Distal tubules, C. Thick ascending limb of Loop of Henle, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: The kidney excretes 250 mmol a day in pro-urine, and resorbs 245 mmol, leading to a net loss in the urine of 5 mmol/d. In addition to this, the kidney processes Vitamin D into calcitriol, the active form that is most effective in assisting intestinal absorption. Both processes are stimulated by parathyroid hormone.Ref: Ganong&;s review of medical physiology; 24th edition; page no:-377