What balances calcium levels in the blood?

The regulation of calcium levels in the blood is primarily governed by parathyroid hormone (PTH). PTH is secreted by the parathyroid glands in response to low calcium levels in the bloodstream. Its main function is to increase blood calcium concentrations through several mechanisms.

When calcium levels drop, PTH promotes the release of calcium from bones, increases reabsorption of calcium in the kidneys, and stimulates the formation of active vitamin D (calcitriol), which enhances calcium absorption from the intestines. Together, these actions effectively raise the calcium levels back to normal range, thus maintaining homeostasis.

Other hormones, such as calcitonin, which is produced by the thyroid gland, work in opposition to PTH but are not primarily responsible for balancing calcium levels in the blood. Additionally, adrenal hormones and insulin do not have a direct role in calcium regulation. Therefore, parathyroid hormone is distinctly responsible for maintaining the balance of calcium levels in the bloodstream.