Which hormone increases blood calcium and decreases phosphate, and is produced by the parathyroid glands?

Which hormone increases blood calcium and decreases phosphate, and is produced by the parathyroid glands?

• A. Calcitonin
• B. Thyroxine
• C. Parathyroid hormone (PTH)
• D. ADH

Answer: (C)

When calcium in the blood drops, the parathyroid glands release parathyroid hormone (PTH). This hormone raises blood calcium through several coordinated actions: it stimulates bone to release calcium into the bloodstream, increases calcium reabsorption in the kidneys so less is lost in urine, and promotes the production of active vitamin D (calcitriol) in the kidneys, which boosts intestinal absorption of calcium. At the same time, PTH decreases phosphate reabsorption in the kidneys, leading to more phosphate being excreted. The overall effect is higher blood calcium and lower phosphate, helping restore balance. Calcitonin, by contrast, lowers blood calcium and is produced by the thyroid. Thyroxine is a metabolic hormone from the thyroid with broader metabolic roles, not specifically calcium regulation. Antidiuretic hormone (ADH) controls water balance in the kidneys, not calcium/phosphate levels.

When calcium in the blood drops, the parathyroid glands release parathyroid hormone (PTH). This hormone raises blood calcium through several coordinated actions: it stimulates bone to release calcium into the bloodstream, increases calcium reabsorption in the kidneys so less is lost in urine, and promotes the production of active vitamin D (calcitriol) in the kidneys, which boosts intestinal absorption of calcium. At the same time, PTH decreases phosphate reabsorption in the kidneys, leading to more phosphate being excreted. The overall effect is higher blood calcium and lower phosphate, helping restore balance.

Calcitonin, by contrast, lowers blood calcium and is produced by the thyroid. Thyroxine is a metabolic hormone from the thyroid with broader metabolic roles, not specifically calcium regulation. Antidiuretic hormone (ADH) controls water balance in the kidneys, not calcium/phosphate levels.