- Parathyroid gland
Name = Parathyroid gland
Latin = glandula parathyroidea inferior, glandula parathyroidea superior, Phillip.Hungerford. Daniel.Mart
GraySubject = 273
GrayPage = 1271
Caption = Endocrine system. (Parathyroid gland not pictured, but are present on surface of thyroid gland, as shown below.)
Caption2 = Thyroid and parathyroid.
neural crest mesenchymeand third and fourth pharyngeal pouch endoderm
superior thyroid artery, inferior thyroid artery,
superior thyroid vein, middle thyroid vein, inferior thyroid vein, thyreoidea ima
middle cervical ganglion, inferior cervical ganglion
MeshName = Parathyroid+Glands
MeshNumber = A06.407.560
DorlandsPre = g_06
The parathyroid glands are small endocrine
glands in the neck, usually located behind the thyroid gland, which produce parathyroid hormone. In rare cases the parathyroid glands are located within the thyroidglands. Most often there are four parathyroid glands, but some people have six or even eight.
The parathyroid glands are four or more small glands located on the posterior surface of the
thyroid gland. Histologically they are quite easily recognizable from the thyroid as they have densely packed cells in contrast with the follicle structure of the thyroid. [BUHistology|15001ooa] However at surgery they are harder to differentiate from the thyroid or fat.
They distinguish themselves from the
thyroid glandhistologically as they contain two types of cells: [BUHistology|15002loa]
The parathyroid glands were discovered by Ivar Viktor Sandström (1852-1889), a Swedish medical student, in
1880. [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 | pmid = 7485136 | doi = 10.1016/0272-6386(95)90447-6] It was the last major organ to be recognized in humans.
The sole function of the parathyroid glands is to maintain the body's
calciumlevel within a very narrow range, so that the nervous and muscular systems can function properly.
calciumlevels 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 proteinthat takes part in the control of calciumand phosphate homeostasis, as well as bone physiology. Parathyroid hormonehas effects antagonistic to those of calcitonin. It increases blood calciumlevels by stimulating osteoclasts to break down bone and release calcium. It also increases gastrointestinal calciumabsorption by activating vitamin D, and promotes calciumuptake by the kidneys.
Role in disease
Hyperparathyroidismand related conditions
The single major disease of parathyroid glands is overactivity of one or more of the parathyroid lobes, which make too much
parathyroid hormonecausing a potentially serious calciumimbalance. This is called hyperparathyroidism; it leads to hypercalcemiaand osteitis fibrosa cystica. Since hyperparathyroidismwas 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
parathyroidmasses, 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 hormonewashings 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
calciumsuggests 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.
Sestamibi scanis often used to determine which parathyroid gland(s) are responsible for overproduction of parathyroid hormone.
Another related condition is called secondary hyperparathyroidism, or secondary HPT - common in patients with chronic kidney disease on dialysis. In secondary HPT, the parathyroid glands make too much parathyroid hormone (PTH), and the kidneys do not produce enough vitamin D, and calcium and phosphorus are out of balance. Even though one may not have any symptoms, treating secondary HPT is important. Cinacalcet (Sensipar) is a medicine that can help treat such dialysis patients and is available by prescription only.
Hypoparathyroidismand related conditions
* Disorders of the
parathyroid hormone receptorhave been associated with Jansen's metaphyseal chondroplasiaand Blomstrand's chondroplasia.
Embryology and Evolution
The parathyroid glands originate from the interaction of
neural crest mesenchymeand third and fourth branchial pouch endoderm.
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
calciumsensing receptors in fish gills with those in the parathryroid glands of birds and mammals is recognized by evolutionary developmental biologyas evolution using genes and gene networks in novel ways to generate new structures with some similar functions and novel functions.
* [http://www.endocrineweb.com/parathyroid.html Endocrine Web at endocrineweb.com]
* [http://www.pnas.org/cgi/content/full/101/51/17716 The origin of the parathyroid gland at pnas.org]
* [http://www.pandasthumb.org/archives/2004/12/human_gland_pro.html Human Gland Probably Evolved From Gills at pandasthumb.org]
* [http://www.blackwell-synergy.com/doi/full/10.1111/j.1469-7580.2005.00472.x The role of the endoderm in the development and evolution of the pharyngeal arches at blackwell-synergy.com]
* [http://www.parathyroid.com Parathyroid disease and treatments discussed in layman's terms at Parathyroid.com]
* [http://scienceblogs.com/pharyngula/2006/06/deep_homologies_in_the_pharyng.php Deep homologies in the pharyngeal arches at scienceblogs.com]
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