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Thyroid-stimulating hormone, beta
Symbol(s): TSHB
Locus: 1 p13
EC number [1]
EntrezGene 7252
OMIM 188540
RefSeq NM_000549
UniProt P01222

Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland.

Genetics

The alpha chain is located on chromosome 6q12-21. The beta chain is located on [[chromosome 13 (human}|Chromosome 13]] 1p13.

Physiology

Controlling the rate of release

TSH stimulates the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3).[1] TSH production is controlled by a Thyrotropin Releasing Hormone, (TRH), which is manufactured in the hypothalamus and transported to the pituitary gland, where it increases TSH production and release. Somatostatin is also produced by the hypothalamus, and has an opposite effect on the pituitary production of TSH, decreasing or inhibiting its release.

The level of Thyroid hormones (T3, T4 and T5) in the blood have an additional effect on the pituitary release of TSH, When the levels of T3 and T4 are low, the production of TSH is increased, and conversely, when levels of T3 and T4 are high, then TSH production is decreased. This effect creates a regulatory negative feedback loop.

Subunits of TSH

TSH is a glycoprotein and consists of two subunits, the alpha and the beta subunit.

The TSH receptor

The TSH receptor is found mainly on thyroid follicular cells. Stimulation of the receptor increases T3 and T4 production and secretion.

Stimulating antibodies to this receptor mimic TSH action and are found in Graves' disease.

Diagnostic use

TSH levels are tested in the blood of patients suspected of suffering from excess (hyperthyroidism), or deficiency (hypothyroidism) of thyroid homone. Generally, a normal range for TSH is between 0.3 and 3.0 mIU/mL, but the interpretation depends also on what the blood levels of thyroid hormones (T3 and T4) are.

Source of pathology TSH level thyroid hormone level Disease causing conditions
hypothalamus/pituitary high high benign tumor of the pituitary (adenoma)
hypothalamus/pituitary low low hypopituitarism
thyroid low high hyperthyroidism or Grave's disease
thyroid high low congenital hypothyroidism (cretinism), hypothyroidism or thyroid hormone resistance

Clearly, both TSH and T3 and T4 should be measured to ascertain where a specific thyroid disfunction is caused by primary pituitary or by a primary thyroid disease. If both are up (or down) then the problem is probably in the pituitary. If the one component (TSH) is up, and the other (T3 and T4) is down, then the disease is probably in the thyroid itself. The same holds for a low TSH, high T3 and T4 finding.

References

  1. Physiology at MCG 5/5ch5/s5ch5_4

External links


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Target-derived NGF, BDNF, NT-3

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