Parathyroid gland
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| Parathyroid gland | |
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| Endocrine system. (Parathyroid gland not pictured, but are present on surface of thyroid gland, as shown below.) | |
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| 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, |
| Nerve | middle cervical ganglion, inferior cervical ganglion |
| Precursor | neural crest mesenchyme and third and fourth pharyngeal pouch endoderm |
The parathyroid glands are small endocrine glands in the neck that produce parathyroid hormone. Humans have four parathyroid glands, which are usually located behind the thyroid gland, and, in rare cases, within the thyroid gland or in the chest. Parathyroid glands control the amount of calcium in the blood and within the bones.
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[edit] Anatomy
The parathyroid glands are four or more small glands located on the posterior surface (back side) of the thyroid gland. The parathyroid glands are named for their proximity to the thyroid but serve a completely different role than the thyroid gland. They are quite easily recognizable from the thyroid as they have densely packed cells, in contrast with the follicle structure of the thyroid. [1] However, at surgery, they are harder to differentiate from the thyroid or fat.
In the histological sense, they distinguish themselves from the thyroid gland, as they contain two types of cells:[2]
| Name | Staining | Quantity | Size | Function |
| parathyroid chief cells | darker | many | smaller | manufacture PTH (see below). |
| oxyphil cells | lighter | few | larger | function unknown.[3] |
[edit] History
The parathyroid glands were discovered by Ivar Viktor Sandström (1852-1889), a Swedish medical student, in 1880.[4] It was the last major organ to be recognized in humans.
[edit] Physiology
The sole function of the parathyroid glands is to maintain the body's calcium level 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 phosphate homeostasis, as well as bone physiology. Parathyroid hormone has effects antagonistic to those of calcitonin. PTH increases blood calcium levels by stimulating osteoclasts to break down bone and release calcium. PTH also increases gastrointestinal calcium absorption by activating vitamin D, and promotes calcium uptake by the kidneys.
[edit] Role in disease
Many conditions are associated with disorders of parathyroid function. These can be divided into those causing hyperparathyroidism, and those causing hypoparathyroidism.
[edit] Embryology and evolution
The parathyroid glands originate from the interaction of neural crest mesenchyme and 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 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.
The superior parathyroids arise from the fourth pharyngeal pouch, and the inferior parathyroids arise from the third pharyngeal pouch. They are vertically transposed during embyrogenesis. This is significant in function-preserving parathyroidectomy, because both the superior and the inferior parathyroids are supplied by the inferior thyroid artery. If the surgeon is to leave a single functional parathyroid for the patient, he/she must preserve the appropriate blood supply.
[edit] Additional images
 Scheme showing development of branchial epithelial bodies. I, II, III, IV. Branchial pouches. |
 Human parathyroid glands |
[edit] References
- ^ Histology at BU 15001ooa
- ^ Histology at BU 15002loa
- ^ Histology at OU 40_06
- ^ Eknoyan G (November 1995). "A history of the parathyroid glands". Am. J. Kidney Dis. 26 (5): 801–7. doi:. PMID 7485136. http://linkinghub.elsevier.com/retrieve/pii/S0272638695002368.
[edit] External links
- Parathyroid disease and treatments discussed in layman's terms at Parathyroid.com
- Parathyroid Surgery and minimal access parathyroid surgery by a UK surgeon
- Endocrine Web at endocrineweb.com
- The origin of the parathyroid gland at pnas.org
- Parathyroid+gland at eMedicine Dictionary
- Virtual Slidebox at Univ. Iowa Slide 149
