Parathyroid gland
From Wikipedia, the free encyclopedia
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 thyroid glands. Most often there are four parathyroid glands but some people have six or even eight.
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[edit] Anatomy
The parathyroid glands are four small glands located on the posterior (closer to the back) surface of the thyroid gland. They distinguish themselves from the thyroid gland histologically as they contain two types of cells- parathyroid chief cells and oxyphil cells. Quite easily recognizable from the thyroid as it has densly packed cell as contrasted by the follicle structure of the thyroid. The parathyroid glands were discovered by Ivar Sandstrom, a Swedish medical student, in 1880. [1] It was the last major organ to be be recognized in humans.
[edit] Physiology
Parathyroid hormone is a small protein that takes part in the control of calcium and phosphorus homeostasis, as well as bone physiology. When blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release hormone into the blood. It then stimulates osteoclasts to break down bone and release calcium into the blood, and increase gastrointestinal calcium absorption. The sole purpose 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.
[edit] Role in disease
Disorders of the parathyroid hormone receptor have been associated with Jansen's metaphyseal chondroplasia and Blomstrand's chondroplasia.
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.
[edit] 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.
[edit] References
- ^ Eknoyan G.. (1995). "A history of the parathyroid glands". Am J Kidney Dis 26 (5): 801-7. PMID 7485136.
[edit] External links
- Endocrine Web
- The origin of the parathyroid gland
- Human Gland Probably Evolved From Gills
- The role of the endoderm in the development and evolution of the pharyngeal arches
- Deep homologies in the pharyngeal arches
| Endocrine system - edit |
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| Adrenal gland | Corpus luteum | Hypothalamus | Kidney | Ovaries | Pancreas | Parathyroid gland | Pineal gland | Pituitary gland | Testes | Thyroid gland |
