PTH role in calcium balance involves which statement?

• A. PTH increases calcium resorption from bone and renal reabsorption, and enhances intestinal absorption via vitamin D
• B. PTH directly stimulates insulin release
• C. PTH reduces phosphate reabsorption in kidney
• D. PTH only affects calcium in bone

Answer: (A)

PTH maintains calcium balance by acting on bone, kidney, and gut to raise serum calcium when it’s low. It increases calcium release from bone by stimulating osteoclast activity, enhances calcium reabsorption in the kidneys so less calcium is lost in urine, and boosts intestinal calcium absorption by stimulating the production of active vitamin D (calcitriol), which increases gut calcium uptake. This combination directly supports higher circulating calcium. While PTH also reduces phosphate reabsorption in the kidney (which helps regulate phosphate), the most complete description of its role in calcium balance is the one that includes bone resorption, renal calcium reabsorption, and intestinal calcium absorption via vitamin D. The other options either describe effects not driven by PTH (like insulin release) or are incomplete (PTH does more than affect bone, and it isn’t limited to bone alone).