parathyroid gland
parathyroid gland
parathyroid gland
parathy′roid gland`
n.
par·a·thy·roid gland
(păr′ə-thī′roid)parathyroid gland
| Noun | 1. | parathyroid gland - any one of four endocrine glands situated above or within the thyroid gland |
n.
parathyroid gland
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
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]parathyroid gland
par·a·thy·roid gland
[TA]parathyroid gland
parathyroid gland
A small gland located at the posterior aspect of the thyroid gland, which regulates calcium by secreting PTH; is critical to calcium and phosphorus metabolism, and magnesium balance and in normal bone mineralization. See PTH.par·a·thy·roid gland
(par'ă-thī'royd gland) [TA]Synonym(s): parathyroid (2) .
parathyroid gland
- noun
Synonyms for parathyroid gland
noun any one of four endocrine glands situated above or within the thyroid gland
Synonyms
- parathyroid
Related Words
- ductless gland
- endocrine gland
- endocrine
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