Management of Patients With Parathyroid Disorders
The parathyroid glands (normally four) are situated in the neck and embedded in the posterior aspect of the thyroid gland (Fig. 42-5). These small glands are easily overlooked and can be removed in-advertently during thyroid surgery. Inadvertent surgical removal is the most common cause of hypoparathyroidism.
Parathormone, the protein hormone from the parathyroid glands, regulates calcium and phosphorus metabolism. Increased secretion of parathormone results in increased calcium absorption from the kidney, intestine, and bones, thereby raising the blood calcium level. Some actions of this hormone are increased by the presence of vitamin D. Parathormone also tends to lower the blood phosphorus level.
Excess parathormone can result in markedly elevated levels of serum calcium, a potentially life-threatening situation. When the product of serum calcium and serum phosphorus (calcium Ã— phosphorus) rises, calcium phosphate may precipitate in various organs of the body and cause tissue calcification.
The serum level of ionized calcium regulates the output of parathormone. Increased serum calcium results in decreased parathormone secretion, creating a negative feedback system.