The parathyroid glands are usually located near the thyroid gland. They produce parathyroid hormone, a hormone that is important for our calcium balance. The parathyroid glands are also called epithelial corpuscles or glandulae parathyroideae. Most people have four epithelial corpuscles, about five percent have five or six, and very rarely there are 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 located?
Normally, the parathyroid glands sit behind our thyroid gland, a pair more toward the upper pole and a pair toward the lower pole. Incidentally, the thyroid gland is located below the larynx in front of the trachea. Sometimes an error in embryonic development also causes the epithelial bodies to be located elsewhere, for example, on the thymus gland behind our sternum. This is usually insignificant, but can complicate surgery.
What is the function of the parathyroid glands?
The parathyroid glands are hormone-producing glands; they make parathyroid hormone (PTH). Parathyroid hormone, along with calcitonin, which is produced in the thyroid gland, and vitamin D, regulates our calcium balance. In doing so, parathyroid hormone acts in three places in our body:
- In the bones, it stimulates the activity of the cells that break down bone. This releases calcium that is stored in the bone.
- In the kidneys, parathyroid hormone increases the reabsorption of calcium and decreases the reabsorption of phosphate from the urine. In turn, a lower level of phosphate in the blood increases calcium. In addition, the kidneys need parathyroid hormone to make vitamin D
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(calcitriol) to form. Without calcitriol, in turn, our body does not absorb calcium. - In the intestine, parathyroid hormone promotes the absorption of calcium from food, for the absorption is vitamin D.
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required.
If the calcium level in the blood rises, the activity of the epithelial bodies decreases and they produce less parathyroid hormone. If the calcium level falls, the inhibition is lifted and more parathyroid hormone is produced again. The exact mechanism of this regulation was not discovered until 1993. Calcitonin is the antagonist of parathyroid hormone. It slows down the breakdown of bone and promotes the excretion of calcium in the kidneys. Thus, it lowers the level of calcium in the blood.
