Parathyroid glands are small endocrine glands in the neck of humans and other tetrapods. Humans usually have four parathyroid glands, located on the back of the thyroid gland in variable locations. The parathyroid gland produces and secretes parathyroid hormone in response to a low blood calcium, which plays a key role in regulating the amount of calcium in the blood and within the bones.
Parathyroid glands share a similar blood supply, venous drainage, and lymphatic drainage to the thyroid glands. Parathyroid glands are derived from the epithelial lining of the third and fourth pharyngeal pouches, with the superior glands arising from the fourth pouch and the inferior glands arising from the higher third pouch. The relative position of the inferior and superior glands, which are named according to their final location, changes because of the migration of embryological tissues.
Hyperparathyroidism and hypoparathyroidism, characterized by alterations in the blood calcium levels and bone metabolism, are states of either surplus or deficient parathyroid function.
The parathyroid glands are four pea-sized glands located on the thyroid gland in the neck. Occasionally, a person is born with one or more of the parathyroid glands embedded in the thyroid, the thymus, or elsewhere in the chest. In most such cases, however, the glands function normally. Though their names are similar, the thyroid and parathyroid glands are entirely separate glands, each producing distinct hormones with specific functions. The parathyroid glands secrete parathyroid hormone (PTH), a substance that helps maintain the correct balance of calcium and phosphorous in the body. PTH regulates release of the calcium from bone, absorption of calcium in the intestine, and excretion of calcium in the urine. When the amount of calcium in the blood falls too low, the parathyroid glands secrete just enough PTH to restore the balance.