parathyroid gland

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Parathyroid gland

An endocrine organ usually associated with the thyroid gland and possessed by all vertebrates except the fishes. In response to lowered serum calcium concentration, a hormone is produced which promotes bone destruction and inhibits the phosphorus-conserving activity of the kidneys. See Thyroid gland

Common positions of human parathyroid glands on the posterior aspect of the thyroidenlarge picture
Common positions of human parathyroid glands on the posterior aspect of the thyroid

In humans, there are typically four glands situated as shown in the illustration; however, the number varies between three and six, with four appearing about 80% of the time. Variations in the positioning of the glands along the craniocaudal axis occur but, excepting parathyroid III which may occasionally be found upon the anterior surface of the trachea, the relation to the posterior surface of the thyroid is rarely lost.

The parathyroid glands are essential for the regulation of calcium and phosphate concentrations in the extracellular fluids of amphibians and higher vertebrates. Parathyroid hormone has two major target organs, bone and kidney. It acts on bone in several ways. Short-term changes include a rapid uptake of bone fluid calcium into osteoblast cells, which in turn pump the calcium into the extracellular fluids. Long-term effects include increased activity and number of osteoclasts, bone cells which act to break down bone matrix and release calcium from bone. All of these effects result in increased blood calcium values. See Bone, Calcium metabolism

Parathyroid hormone inhibits the renal reabsorption of phosphate, thus increasing the urinary output of phosphate. Phosphate reabsorption across the renal tubule is dependent upon sodium transport, and parathyroid hormone interferes with this sodium-dependent phosphate transport in the proximal tubule. Another important effect of parathyroid hormone on the kidney is to increase the renal reabsorption of calcium, thus reducing the loss of calcium in the urine and conserving calcium in the body. See Kidney

Finally, there are reports that parathyroid hormone indirectly stimulates calcium uptake into the body across the intestine. Parathyroid hormone stimulates the production of the most active metabolite of vitamin D, 1,25-dihydroxycholecalciferol, during vitamin D synthesis. This metabolite of vitamin D directly stimulates the intestinal absorption of calcium. See Endocrine system (vertebrate), Parathyroid hormone

parathyroid gland

[¦par·ə′thī‚rȯid ‚gland]
A paired endocrine organ located within, on, or near the thyroid gland in the neck region of all vertebrates except fishes.
References in periodicals archive ?
As small as peppercorns, the four parathyroid glands in the neck nevertheless pack a big punch.
Excess ionized calcium decreases the parathyroid gland secretion of PTH, the principal hormone that increases serum calcium.
Camacho also says that there are various treatments for parathyroid gland disorder, depending on its cause.
A normal parathyroid gland is not visible via US, and an abnormal adenoma is usually not palpable.
The inferior parathyroid gland, from the third pharyngeal pouch, migrates with the thymus caudally to lie on the dorsal surface of the inferior aspect of the thyroid gland.
Parathyroid glands are usually 4 in number, each measuring 5 mm in diameter.
AMG 416 acts by binding to and activating the calcium-sensing receptor on the parathyroid gland, thereby causing decreases in PTH.
Technetium-99m sestamibi imaging is one of the most helpful studies for localizing hyperfunctioning parathyroid gland tissue.
Other contributing factors include direct trauma to the parathyroid gland, inadvertent gland removal, hemodilution, "hungry bone syndrome," and thyrotoxic osteodystrophy (7).
Pathological examination of the surgical specimen revealed nodular goiter, thymic tissue, and a normal appearing parathyroid gland.