What is the primary function of parathyroid hormone (PTH)?

The primary function of parathyroid hormone (PTH) is to increase blood calcium levels. PTH is secreted by the parathyroid glands, which are located behind the thyroid gland in the neck. When blood calcium levels drop below a certain threshold, PTH is released into the bloodstream and exerts its effects on various target tissues to elevate calcium concentrations.

PTH triggers the release of calcium from bones by stimulating osteoclasts, the cells responsible for bone resorption. This process releases calcium stored in the bone matrix into the circulatory system. Moreover, PTH enhances renal tubular reabsorption of calcium, minimizing calcium loss in urine. It also promotes the conversion of vitamin D into its active form, calcitriol, which increases intestinal absorption of calcium from dietary sources.

Through these mechanisms, PTH plays a vital role in maintaining calcium homeostasis and contributing to the body's metabolic processes that rely on calcium as a critical mineral.