The parathyroid glands are usually located near the thyroid gland. They produce parathyroid hormone, which is important for our calcium metabolism. The parathyroid glands are also called epithelial bodies or glandulae parathyroideae. Most people have four epithelial bodies, about five percent have five or six, very rarely come even only three. A single parathyroid gland is about the size of a lens and weighs between 30 and 70 milligrams.
Where are the parathyroid glands?
Normally, the parathyroid glands are behind our thyroid gland, one at the top and one at the bottom. Incidentally, the thyroid lies below the larynx in front of the trachea. Sometimes a mistake in embryonic development also causes the epithelial bodies to sit elsewhere, for example, on the thymus gland behind our sternum. This is usually negligible, but can complicate an operation.
What function do the parathyroid glands have?
The parathyroid glands are hormone-producing glands, they produce the parathyroid hormone (PTH). Parathyroid hormone, together with calcitonin, which is produced in the thyroid gland, and vitamin D regulate our calcium metabolism. Parathyroid hormone acts on three parts of our body:
- In the bones, it stimulates the activity of bone-degrading cells. This releases calcium stored in the bone.
- In the kidneys, parathyroid hormone increases the reuptake of calcium and diminishes the reuptake of phosphate from the urine. By a lower phosphate level in the blood again increases the calcium content. In addition, the kidneys require parathyroid hormone to produce vitamin D 3 (calcitriol). Without calcitriol, our body does not absorb calcium.
- In the intestine parathyroid hormone promotes the absorption of calcium from the diet, for the absorption of vitamin D 3 is needed.
If the calcium content in the blood increases, the activity of the epithelial bodies decreases and they form less parathyroid hormone. If the calcium level drops, the inhibition is reversed and more parathyroid hormone is produced again. The exact mechanism of this regulation was discovered only in 1993. Calcitonin is the antithesis of the parathyroid hormone. It slows down the breakdown of bones and promotes the excretion of calcium in the kidneys. This lowers the level of calcium in the blood.