Which hormone regulates calcium levels in the blood?

The hormone that regulates calcium levels in the blood is parathyroid hormone. This hormone is secreted by the parathyroid glands and plays a crucial role in maintaining calcium homeostasis. When calcium levels in the blood drop below normal, parathyroid hormone is released into the bloodstream.

Parathyroid hormone acts on several target organs to increase blood calcium levels. It stimulates the release of calcium from bones, promotes calcium reabsorption in the kidneys, and enhances the absorption of dietary calcium in the intestines by increasing the active form of vitamin D. This coordinated response effectively raises calcium levels back to the desired range.

While other hormones, such as calcitonin, also have roles in calcium metabolism—primarily by lowering blood calcium levels—parathyroid hormone is essential for increasing these levels when they fall too low. Insulin and cortisol do not directly regulate calcium levels in the blood; their primary functions relate to glucose metabolism and the body's stress response, respectively. Thus, the role of parathyroid hormone in calcium regulation is a critical aspect of maintaining overall metabolic balance and skeletal health.