Which hormone is responsible for regulating calcium levels in the blood?

Parathyroid hormone (PTH) is the key hormone involved in regulating calcium levels in the blood. It is produced by the parathyroid glands, which are located near the thyroid gland in the neck. PTH plays a vital role in maintaining calcium homeostasis by increasing blood calcium levels when they become too low. It does this through several mechanisms: it stimulates the release of calcium from bones, increases the absorption of calcium in the intestines by promoting the activation of vitamin D, and enhances the reabsorption of calcium in the kidneys to reduce calcium excretion.

In the context of the other hormones listed, insulin primarily regulates glucose metabolism, glucagon works to raise blood glucose by promoting the release of glucose from the liver, and aldosterone is mainly involved in regulating sodium and potassium levels as well as blood pressure. Thus, PTH stands out as the specific hormone that directly affects calcium regulation in the bloodstream.