Difference between revisions of "Parathyroid gland" - New World Encyclopedia
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| − | The '''parathyroid glands''' are small [[endocrine system|endocrine]] [[gland]]s in | + | The '''parathyroid glands''' are small [[endocrine system|endocrine]] [[gland]]s found in all [[vertebrate]]s except [[fish]] and that produce [[parathyroid hormone]], which regulates [[calcium]] and [[phosphate]] levels in the extracellular fluids. The parathyroid gland generally is located near the [[thyroid]] gland. |
| − | + | In humans, there most often are four parathyroid glands, in pairs of two, but some people have has few as two or three, and as many as six or even eight. The human parathyroid glands are located in the neck, unually on the posterior surface of the thyroid gland, although in rare cases they may be located within the [[thyroid]] gland. | |
| − | The parathyroid glands are | ||
| − | They distinguish themselves from the thyroid gland histologically as they contain two types of cells: | + | ==Overview== |
| + | Parathyroid glands are considered part of the [[endocrine system]], which is a control system of ductless glands and single [[cell (biology)|cells]] that secrete chemical messengers called [[hormone]]s. These hormones pass directly from the glands into the body and are transmitted through the [[blood]] or via diffusion, rather than being secreted through tubes. | ||
| + | |||
| + | In the case of the parathyroid glands, this chemical messanger is the parathyroid hormone or parathormone. It acts to regulate calcium and phosphate [[metabolism]], targeting movement of calcium from [[bone]]s into extracellular fluids (increasing calcium in the fluids); inhibiting renal reabsorption of phosphate (increasing loss of phosphate from the body); and elevating renal reabsorption of calcium (increasing retention of calcium). | ||
| + | |||
| + | The parathyroid glands were discovered by Ivar Sandstrom, a Swedish medical student, in 1880 (Eknoyan 1995). It was the last major organ to be recognized in humans. | ||
| + | |||
| + | ==Anatomy in humans== | ||
| + | Parathyroid glands are quite easily recognizable from the thyroid as they have densely packed [[cell (biology)|cells]] in contrast with the follicle structure of the thyroid. They distinguish themselves from the thyroid gland histologically as they contain two types of cells: | ||
{| class="wikitable" | {| class="wikitable" | ||
| '''Name''' || '''Staining''' || '''Quantity''' || '''Size''' || '''Function''' | | '''Name''' || '''Staining''' || '''Quantity''' || '''Size''' || '''Function''' | ||
|- | |- | ||
| − | | [[parathyroid chief cell]]s || darker || many | + | | [[parathyroid chief cell]]s || darker || many || smaller || manufacture PTH (see below). |
|- | |- | ||
| − | | [[oxyphil cell]]s || lighter || few || larger || function unknown. | + | | [[oxyphil cell]]s || lighter || few || larger || function unknown. |
|} | |} | ||
| − | |||
| − | |||
==Physiology== | ==Physiology== | ||
| − | The sole function of the parathyroid glands is to regulate the calcium level in our bodies within a very narrow range so that the nervous and muscular systems can function properly. | + | The sole function of the parathyroid glands is to regulate the calcium level in our bodies within a very narrow range so that the [[nervous system|nervous]] and muscular systems can function properly. |
| − | When blood calcium levels drop below a certain point, calcium-sensing | + | When [[blood]] calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release hormone into the blood. |
| − | [[Parathyroid hormone]] (PTH, also known as parathormone) is a small [[protein]] that takes part in the control of [[calcium]] and [[phosphorus]] | + | [[Parathyroid hormone]] (PTH, also known as parathormone) is a small [[protein]] that takes part in the control of [[calcium]] and [[phosphorus]] homeostasis, as well as bone physiology. It acts on both [[bone]] and the kidney. In the bone tissue, PTH causes update of calcium from the bone fluid, resulting in its movement into the extracellular fluids and blood. It also stimulates [[osteoclast]]s to break down bone and release calcium into the blood. In the kidney, PTH increases calcium reabsorption such that not as much is lost in the urine, while at the same time decreasing phosphate reabsorption, thus increasing loss through the urine. It is also believed that PTH increases gastrointestinal calcium absorption. |
| − | |||
| − | It | ||
==Role in disease== | ==Role in disease== | ||
| Line 81: | Line 84: | ||
==References== | ==References== | ||
<references/> | <references/> | ||
| + | |||
| + | <ref>{{cite journal | author = Eknoyan G.. | title = A history of the parathyroid glands | journal = Am J Kidney Dis | volume = 26 | issue =5| pages = 801-7 | year =1995 | id = PMID 7485136 }}</ref> | ||
== External links == | == External links == | ||
Revision as of 02:59, 10 May 2007
| Parathyroid gland | |
|---|---|
 | |
| Endocrine system. (Parathyroid gland not pictured, but are present on surface of thyroid gland, as shown below.) | |
 | |
| Thyroid and parathyroid. | |
| Latin | glandula parathyroidea inferior, glandula parathyroidea superior |
| Gray's | subject #273 1271 |
| Artery | superior thyroid artery, inferior thyroid artery, |
| Vein | superior thyroid vein, middle thyroid vein, inferior thyroid vein, thyreoidea ima |
| Nerve | middle cervical ganglion, inferior cervical ganglion |
| Precursor | neural crest mesenchyme and third and fourth pharyngeal pouch endoderm |
| MeSH | Parathyroid+Glands |
| Dorlands/Elsevier | g_06/{{{DorlandsSuf}}} |
The parathyroid glands are small endocrine glands found in all vertebrates except fish and that produce parathyroid hormone, which regulates calcium and phosphate levels in the extracellular fluids. The parathyroid gland generally is located near the thyroid gland.
In humans, there most often are four parathyroid glands, in pairs of two, but some people have has few as two or three, and as many as six or even eight. The human parathyroid glands are located in the neck, unually on the posterior surface of the thyroid gland, although in rare cases they may be located within the thyroid gland.
Overview
Parathyroid glands are considered part of the endocrine system, which is a control system of ductless glands and single cells that secrete chemical messengers called hormones. These hormones pass directly from the glands into the body and are transmitted through the blood or via diffusion, rather than being secreted through tubes.
In the case of the parathyroid glands, this chemical messanger is the parathyroid hormone or parathormone. It acts to regulate calcium and phosphate metabolism, targeting movement of calcium from bones into extracellular fluids (increasing calcium in the fluids); inhibiting renal reabsorption of phosphate (increasing loss of phosphate from the body); and elevating renal reabsorption of calcium (increasing retention of calcium).
The parathyroid glands were discovered by Ivar Sandstrom, a Swedish medical student, in 1880 (Eknoyan 1995). It was the last major organ to be recognized in humans.
Anatomy in humans
Parathyroid glands are quite easily recognizable from the thyroid as they have densely packed cells in contrast with the follicle structure of the thyroid. They distinguish themselves from the thyroid gland histologically as they contain two types of cells:
| Name | Staining | Quantity | Size | Function |
| parathyroid chief cells | darker | many | smaller | manufacture PTH (see below). |
| oxyphil cells | lighter | few | larger | function unknown. |
Physiology
The sole function of the parathyroid glands is to regulate the calcium level in our bodies within a very narrow range so that the nervous and muscular systems can function properly.
When blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release hormone into the blood.
Parathyroid hormone (PTH, also known as parathormone) is a small protein that takes part in the control of calcium and phosphorus homeostasis, as well as bone physiology. It acts on both bone and the kidney. In the bone tissue, PTH causes update of calcium from the bone fluid, resulting in its movement into the extracellular fluids and blood. It also stimulates osteoclasts to break down bone and release calcium into the blood. In the kidney, PTH increases calcium reabsorption such that not as much is lost in the urine, while at the same time decreasing phosphate reabsorption, thus increasing loss through the urine. It is also believed that PTH increases gastrointestinal calcium absorption.
Role in disease
The single major disease of parathyroid glands is overactivity of one or more of the parathyroid lobes which make too much parathyroid hormone causing a potentially serious calcium imbalance. This is called hyperparathyroidism; it leads to hypercalcemia and osteitis fibrosa cystica. Since hyperparathyroidism was first described in 1925, the symptoms have become known as "moans, groans, stones, and bones." The primary treatment for this disease is the surgical removal of the faulty gland.
Modern high frequency ultrasound can see parathyroid masses, even before they cause high calcium. They are called parathyroid incidentalomas. If a patient has elevated calcium, the ultrasound can be used to locate the abnormal glands. The use of ultrasound guided FNA, and parathyroid hormone washings can confirm the abnormal glands. A blood calcium 15-30 minutes after the biopsy can help determine if the disease is caused by a single abnormal gland or multiple glands.
A drop in serum calcium suggests a single source, and no drop suggests multiple glands. This, with a non-localizing Sestamibi scan would point toward a neck exploration, rather than a minimally invasive method aimed a single gland disease.
A Sestamibi scan is often used to determine which parathyroid gland(s) are responsible for overproduction of parathyroid hormone.
- Hypoparathyroidism
- Pseudohypoparathyroidism
- Pseudopseudohypoparathyroidism
- Disorders of the parathyroid hormone receptor have been associated with Jansen's metaphyseal chondroplasia and Blomstrand's chondroplasia.
Embryology and Evolution
The parathyroid glands originate from the interaction of neural crest mesenchyme and third and fourth pharyngeal pouch endoderm.
Genetically, Eya-1 (transcripitonal co-activator), Six-1 (a homeobox transcription factor), and Gcm-2 (a transcription factor) have been associated with the development of the parathyroid gland, and alterations in these genes alters parathyroid gland development.
The conserved homology of genes and calcium sensing receptors in fish gills with those in the parathryroid glands of birds and mammals is recognized by Evolutionary developmental biology as evolution using genes and gene networks in novel ways to generate new structures with some similar functions and novel functions.
Additional images
Scheme showing development of branchial epithelial bodies. I, II, III, IV. Branchial pouches.
Human parathyroid glands
ReferencesISBN links support NWE through referral fees
External links
- Parathyroid surgery discussed by a UK specialist including minimal access surgery
- Parathyroid disease and treatments discussed in layman's terms at Parathyroid.com
- Endocrine Web at endocrineweb.com
- The origin of the parathyroid gland at pnas.org
- Human Gland Probably Evolved From Gills at pandasthumb.org
- The role of the endoderm in the development and evolution of the pharyngeal arches at blackwell-synergy.com
- Deep homologies in the pharyngeal arches at scienceblogs.com
- Template:EMedicineDictionary
- Template:USCHistology
- Template:IowaHistologyInteractive
| Endocrine system - edit |
|---|
| Adrenal gland | Corpus luteum | Hypothalamus | Kidney | Ovaries | Pancreas | Parathyroid gland | Pineal gland | Pituitary gland | Testes | Thyroid gland |
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- ↑ Eknoyan G.. (1995). A history of the parathyroid glands. Am J Kidney Dis 26 (5): 801-7. PMID 7485136.
