What are the parathyroids?
The parathyroid glands are four (in most people) button-sized glands that are located near the thyroid gland at the base of the throat. Each parathyroid gland produces parathyroid hormone (PTH), which helps to regulate the amount of calcium in the blood.
Calcium is a mineral that is essential for the proper functioning of muscles, nerves, and the heart and is required in blood clotting and in the formation of bones. About 99% of calcium is found in the teeth and bones while most of the remaining 1% circulates in the blood. Some calcium is lost from the body every day, filtered from the blood by the kidneys and excreted into the urine.
To regulate blood calcium, PTH functions as part of a feedback system that involves calcium, phosphorus (as phosphate), and vitamin D. Phosphorus is another mineral that works with calcium in its different functions in the body. Most of it binds with calcium to help form bones and teeth. Vitamin D promotes the absorption of calcium in the intestines.
The role of the parathyroid glands is to ensure that the concentration of calcium in blood remains within a fairly narrow range. As the level of calcium in the blood drops, the parathyroid glands produce and release PTH, which works in three ways to boost calcium in the blood:
- PTH acts on the kidneys to reduce the excretion of calcium in urine and to promote the elimination of phosphate in the urine.
- It stimulates the kidneys to convert vitamin D from the inactive to the active form. This in turn increases the amount of calcium absorbed from food in the intestines.
- It promotes the release of calcium from bones into the bloodstream.
As the level of calcium in the blood increases, the production of PTH by the parathyroid glands falls. This feedback system normally maintains a dynamic but relatively stable concentration of calcium in the blood.