Which hormone initially increases calcium and phosphate release after bone resorption and then excretes phosphate?

• A. Calcitonin
• B. PTH
• C. Vitamin D
• D. Growth hormone

Answer: (B)

Parathyroid hormone drives this pattern. It rapidly promotes bone resorption, releasing calcium and phosphate into the bloodstream. In the kidney, PTH then moves to conserve calcium by increasing its reabsorption, while simultaneously reducing phosphate reabsorption, which causes phosphate to be excreted in urine. PTH also stimulates the formation of active vitamin D, which increases intestinal absorption of calcium and phosphate, reinforcing the calcium rise while phosphate is eliminated renally. This sequence—bone release followed by renal phosphate excretion—fits the described effect. Other hormones don’t produce this combination: calcitonin lowers bone resorption and calcium; vitamin D raises intestinal phosphate (not excretion); growth hormone doesn’t cause this specific phosphate excretion pattern.