What is the primary function of parathyroid hormone?

• A. Metabolism of calcium and phosphorus
• B. Regulation of blood glucose levels
• C. Regulation of thyroid hormone production
• D. Stimulation of red blood cell production

Answer: (A)

Calcium balance in the blood is what parathyroid hormone controls. When calcium levels drop, the parathyroid glands release this hormone, which raises serum calcium through several coordinated actions. It stimulates bone to release calcium by activating osteoclasts, increases calcium reabsorption in the kidneys, and promotes the activation of vitamin D, which boosts calcium (and phosphate) absorption from the gut. The overall effect is to restore normal calcium—and phosphate—levels in the blood, keeping them in balance. This is why the correct description involves metabolism and regulation of calcium and phosphorus. The other options describe functions for different hormones (glucose regulation, thyroid hormone production, red blood cell production) and do not reflect PTH’s role.