Parathyroid Gland
Parathyroid Gland is any of a group of glandular cell aggregations located in the neck region close to the thyroid gland in lizards, some birds, and most mammals. In humans, four such clumps are usually present as distinct, yellowish-brown, encapsulated organs, each about 6 mm (‚ in) long. The combined weight of these glands is no more than 560 mg (1/50 oz). They are located beneath the thyroid gland; one or more of them are occasionally embedded in the thyroid tissue. Sometimes they may appear in association with the thymus, or anywhere between the thyroid and thymus, or even elsewhere in the neck or upper anterior chest. Such glands, which may be present in addition to four normally placed ones, are known as accessory parathyroid tissue. The parathyroid glands secrete a hormone known as parathormone, which controls the concentration of calcium (calcium ion) and phosphorus (phosphate) in the blood. Calcium and phosphorus normally have a relationship to each other that the body keeps f...