Which hormone raises blood calcium by promoting bone resorption?

• A. Parathyroid Hormone
• B. Calcitonin
• C. Vitamin D
• D. Calciferol

Answer: (A)

Raising blood calcium by promoting bone resorption is the action of parathyroid hormone. When calcium levels drop, the parathyroid glands release this hormone, which signals bone cells to increase osteoclast activity via osteoblasts producing RANKL. That stimulates bone breakdown and calcium release into the blood. PTH also increases calcium reabsorption in the kidneys and stimulates activation of vitamin D to calcitriol, which boosts calcium absorption from the gut. By contrast, calcitonin lowers blood calcium by inhibiting osteoclasts, while vitamin D and calciferol mainly enhance intestinal calcium absorption and bone mineralization rather than driving bone resorption. So the hormone that raises blood calcium through promoting bone resorption is parathyroid hormone.