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|Thyroid-stimulating hormone, beta|
Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a thyroid hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland.
Controlling the rate of releaseEdit
TSH stimulates the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3). 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 TSHEdit
TSH is a glycoprotein and consists of two subunits, the alpha and the beta subunit.
- The α (alpha) subunit is identical to that of human chorionic gonadotropin (HCG), luteinising hormone (LH), follicle-stimulating hormone (FSH).
- The β (beta) subunit is unique to TSH, and therefore determines its function.
The TSH receptorEdit
Stimulating antibodies to this receptor mimic TSH action and are found in Graves' disease.
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)|
|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.
|Hormones and endocrine glands - edit|
Hypothalamus: - TRH - CRH - GnRH - GHRH - somatostatin - dopamine | Posterior pituitary: vasopressin - oxytocin - lipotropin | Anterior pituitary: GH - ACTH - TSH - LH - FSH - prolactin - MSH - endorphins - lipotropin
Thyroid: T3 and T4 - calcitonin | Parathyroid: PTH | Adrenal medulla: epinephrine - norepinephrine | Adrenal cortex: aldosterone - cortisol - DHEA | Pancreas: glucagon- insulin - somatostatin | Ovary: estradiol - progesterone - inhibin - activin | Testis: testosterone - AMH - inhibin | Pineal gland: melatonin | Kidney: renin - EPO - calcitriol - prostaglandin | Heart atrium: ANP
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