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

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Further studies are required to clarify whether the same possible molecular or cellular change is also the cause of the ectopic location of the parathyroid gland.
Our policy for total thyroidectomy is to preserve parathyroid glands and its vascularity.
The parathyroid glands are generally located in the cervical region, just behind the thyroid gland.
Although the normal parathyroid glands are usually not visualised with available sonographic technology, enlarged parathyroid glands may be visualised.
The underlying pathophysiology was supposed to be either a common genetic predisposition or the extension of the autoimmune process to the parathyroid glands, which is still under debate (12).
A hundred nineteen patients (20.4%) were presented as parathyroid gland diseases, a follow-up was considered in 4 patients.
Four different-sized macroscopic biopsy specimens from parathyroid glands were sent to the Pathology Department of the Erciyes University Medicine Faculty.
Mody, "Histopathological changes of the thyroid and parathyroid glands in HIV-infected patients," Journal of Thyroid Research, vol.
In addition, the technique was considered to be appropriate to access the parathyroid gland with the antecedent removal of the thyroid gland.
A slightly enlarged left lower parathyroid gland that was excised under the suspicion that adenoma was evidenced.