Which hormone increases blood calcium levels?

Parathyroid hormone (PTH) plays a crucial role in regulating calcium levels in the blood. When blood calcium levels decrease, PTH is released from the parathyroid glands. This hormone increases blood calcium levels through several mechanisms.

First, PTH stimulates the release of calcium from bones into the bloodstream by promoting the activity of osteoclasts, which are cells responsible for bone resorption. Secondly, PTH enhances the absorption of calcium in the intestines by activating vitamin D, which in turn increases intestinal calcium absorption. Additionally, PTH reduces the excretion of calcium by the kidneys, allowing more calcium to be retained in the body.

In contrast, calcitonin is a hormone that lowers blood calcium levels by inhibiting osteoclast activity and promoting calcium deposition in bones. Insulin mainly regulates glucose levels in the blood and is not directly involved in calcium regulation. Cortisol, a steroid hormone, has a complex role that can include effects on calcium metabolism, but it does not primarily function to increase blood calcium levels like PTH does. Therefore, PTH is recognized as the key hormone that specifically increases blood calcium levels.