The parathyroid glands are tiny organs located behind the thyroid gland. Each parathyroid is about half the size of a grain of rice. Although they are called “para”-thyroid glands, they are actually quite different from the thyroid gland. They are occasionally referred to as “epithelial bodies.” While there is some variation, people usually have four parathyroid glands located behind the thyroid. Specifically, the parathyroids are situated on the upper and lower portions on the back of the thyroid gland’s left and right lobes.
The parathyroid glands secrete parathyroid hormone. Unlike thyroid hormones, parathyroid hormone mediates calcium metabolism. Calcium is not only the primary material in bone, but also essential for clotting blood and muscle contraction throughout the body, including the heart. Furthermore, calcium is a mineral that is essential for the proper functioning of brain cells.
Calcium is stored in bone. Parathyroid hormone works in combination with vitamin D to increase levels of calcium in the blood by releasing it from bone as well as absorbing it in the intestines and kidneys.
Calcium also functions to regulate the secretion of parathyroid hormone. If blood calcium levels decrease, then the secretion of parathyroid hormone will increase in order to elevate blood calcium levels. On the other hand, if blood calcium levels are too high, the secretion of parathyroid hormone will decrease and lower blood calcium levels. This process works to keep the blood calcium level stable.