The parathyroid or parathyroid glands ensure the production and the endocrine secretion (internal) of a parathyroid hormone, a particular hormone essential in regulating the metabolism of minerals (particularly calcium and phosphorus) within the organism.

The parathyroid glands have a specific, encapsulated and smooth surface and they have a light brown colour due to their fat content, percentage of oxyphil cells in the glands and their vascularity. The presence of yellow colour around the glands may be mistaken for surrounding fat.


What are the parathyroid glands?

The parathyroid glands have a limited size and are approximately 0.5-1 cm. Covered by a fibrous capsule, within which they contain cells arranged in cord that are divisible into three types: principal cells (small and polyhedral shape), clear cells  (relatively large) and oxyphil cells (cells that present the oxyphil in the cytoplasm, or acidophilus granules). 

The parathyroid glands are located behind the thyroid gland, and in general include four glands (or two pairs of parathyroid glands), but there may also be five or six glands. Their name reflects the close relationship with the thyroid gland. Usually there are two parathyroid glands: upper and two lower parathyroid glands or superior and inferior parathyroid glands. The upper pair of parathyroid is usually located behind the thyroid, while the lower pair of parathyroid is located between the branches of the inferior thyroid.

The superior parathyroid glands receive blood supply through the inferior thyroid artery or through an anastomotic branch located between the inferior and superior thyroid artery. On the other hand, the inferior thyroid artery usually supplies the inferior parathyroid glands. In cases where the inferior thyroid artery is absent, a branch from the superior thyroid artery supplies the inferior parathyroid glands.


What function do the parathyroid glands serve?

The main responsibility of the parathyroid glands is to regulate the levels of calcium in the body within a limited range in order for the muscular and nervous systems to function properly.

Calcium is the main element that causes muscles to contract, it is the main structural element of bones, which provides bone rigidity, and it is important to the normal conduction of electrical currents along nerves.

Any reduction of calcium levels below normal signals the parathyroid glands to start producing the parathyroid hormone, which controls the calcium levels in the body.

Moreover, the function of the parathyroid glands is to produce and secrete parathyroid hormone, or PTH. A chain of 84 amino acids whose job is to preside over the regulation of calcium/phosphate in the body by participating in mechanisms that control the presence of calcium in the blood and maintain healthy bones makes this hormone. In the kidneys it stimulates the reabsorption of calcium and excretion of phosphate, while in the intestine the parathyroid hormone stimulates the absorption of calcium.

The production of this hormone causes the transfer of calcium from bone to blood; however its deficiency causes a reduction of the level of calcium in the blood, resulting in the occurrence of a state of hypertonic muscle (confirming the fundamental role that calcium plays in the regulation muscle contraction).