Which hormone regulates calcium levels in the blood?

Parathyroid hormone (PTH) plays a crucial role in regulating calcium levels in the blood. It is produced by the parathyroid glands and primarily functions to increase calcium concentrations in the bloodstream. PTH achieves this by stimulating the release of calcium from bones, enhancing intestinal absorption of calcium through the activation of vitamin D, and promoting renal reabsorption of calcium, thus reducing the amount excreted in urine. This orchestrated response ensures that calcium levels remain within a tightly regulated range, which is vital for various physiological processes, including muscle contraction, blood clotting, and nerve function.

In contrast, while calcitonin also influences calcium metabolism, it primarily works to lower blood calcium levels by inhibiting bone resorption and promoting calcium excretion in the kidneys. Insulin is primarily involved in glucose metabolism and has no direct role in calcium regulation, and growth hormone is mainly responsible for growth and metabolism, impacting processes such as muscle and bone growth but does not regulate blood calcium levels directly.