What is the role of parathyroid hormone?

Parathyroid hormone (PTH) plays a critical role in regulating calcium homeostasis in the body. When blood calcium levels drop, the parathyroid glands release PTH, which works to increase the concentration of calcium in the bloodstream. It achieves this through several mechanisms:

1. Bone Resorption: PTH acts on osteoclasts, the cells responsible for bone breakdown, leading to the release of calcium from bones into the bloodstream.

2. Kidney Function: PTH enhances calcium reabsorption in the kidneys, reducing calcium loss in urine. It also stimulates the conversion of vitamin D to its active form, calcitriol, which further increases intestinal absorption of calcium.

3. Intestinal Absorption: The increase in active vitamin D enhances the absorption of dietary calcium in the intestines, contributing to the overall rise in blood calcium levels.

Each of these actions confirms that the primary function of parathyroid hormone is to increase blood calcium levels, which is vital for various physiological processes, including bone health, muscle function, and nerve signaling.