thyrotropin


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thyrotropin

(thī'rätrō`pĭn) or

thyroid-stimulating hormone

(TSH), hormonehormone,
secretory substance carried from one gland or organ of the body via the bloodstream to more or less specific tissues, where it exerts some influence upon the metabolism of the target tissue.
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 released by the anterior pituitary glandpituitary gland,
small oval endocrine gland that lies at the base of the brain. It is sometimes called the master gland of the body because all the other endocrine glands depend on its secretions for stimulation (see endocrine system).
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 that stimulates the thyroid glandthyroid gland,
endocrine gland, situated in the neck, that secretes hormones necessary for growth and proper metabolism. It consists of two lobes connected by a narrow segment called the isthmus. The lobes lie on either side of the trachea, the isthmus in front of it.
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 to release thyroxinethyroxine
, substance secreted by the thyroid gland. The hormone thyroxine forms by combining the amino acid tyrosine with iodine. Complexed to a protein, it is stored in the follicle stems between thyroid cells.
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. The release of thyrotropin is triggered by the action of thyrotropin-releasing factor (TRF), a substance found in the hypothalamus of the brain. TRF, once released from the hypothalamus, travels in the bloodstream to the anterior pituitary, where it causes the release of thyrotropin. This latter substance, a glycoprotein (see proteinprotein,
any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight.
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), is carried to the thyroid gland by the blood, where it stimulates the uptake of iodine, the conversion of diiodotyrosine to thyroxine, and the secretion of thyroid hormones into the bloodstream. Thyroxine inhibits the further release of thyrotropin by interfering with the action of TRF; thus the levels of thyroid hormones are regulated. If not enough iodine is available in the diet, then not enough thyroxine will be made to shut off the release of thyrotropin. Prolonged stimulation of the thyroid by thyroid-stimulating hormone results in an abnormal enlargement of the gland, known as goiter, a condition which has been largely eradicated by the widespread usage of iodized salt.

Thyrotropin

 

(thyrotropic hormone, thyroid-stimulating hormone, TSH), a hormone produced by the anterior lobe of the hypophysis in vertebrate animals and man that controls the development and functions of the thyroid gland. Thyrotropin is a glycoprotein with a molecular weight of 28,000–30,000. It stimulates the splitting of the protein thyroglobulin in the thryoid follicles and the release of the active thyroid hormones, thyroxine and triiodothyronine, into the blood. It also promotes the enlargement of follicular cells, the absorption of iodine, and the synthesis of thyroxine.

The mechanism of action of thyrotropin, like that of several other hormones, is related to the hormone’s capacity to activate the synthesis of cyclic adenylic acid (cAMP), which stimulates the splitting of thyroglobulin. The synthesis and secretion of thyrotropin are controlled by the central nervous system and, primarily, by the hypothalamus, which produces the special thyrotropin releasing factor. When the concentration of thyroid hormones in the blood increases, the hormones inhibit by negative feedback the secretion of thyrotropin by acting both on the hypothalamic regulatory centers and directly on the hypophysis, causing the secretion of thyroxine and triiodothyronine to diminish. Epinephrine and the corticosteroids also suppress the secretion of thyrotropin, which accounts for the decrease in thyroid activity in various stress reactions (except cold stress). (See alsoADAPTATION SYNDROME and NEUROSECRETION.)

I. V. KRIUKOVA

thyrotropin

[thī′rä·trə·pən]
(biochemistry)
A thyroid-stimulating hormone produced by the adenohypophysis.
References in periodicals archive ?
Recent studies in man and other mammalian species have shown that adipocytes and preadipocytes possess thyrotropin receptors.
Serum thyrotropin concentration as a novel predictor of malignancy in thyroid nodules investigated by fine-needle aspiration.
Vassart, "Somatic mutations causing constitutive activity of the thyrotropin receptor are the major cause of hyperfunctioning thyroid adenomas: Identification of additional mutations activating both the cyclic adenosine 3',5'-monophosphate and inositol phosphate-Ca2+ cascades," Molecular Endocrinology, vol.
A circulating,biologically inactive thyrotropin caused by a mutation in the beta subunit gene.
The positive regulation of human thyrotropin (TSH) receptor messenger ribonucleic acid by recombinant human TSH is at the intranuclear level.
Janssen, "Sensitive thyrotropin and thyrotropin-receptor antibody determinations one month after discontinuation of antithyroid drug treatment as predictors of relapse in Graves' disease," Thyroid, vol.
Thyrotropin depended on the number of pregnancies (p=0.006) with significant differences in TSH among women with one pregnancy compared to those who had none (p=0.038) or at least 2 pregnancies (p=0.004) (Table 1); no dependency of TSH on either age (p=0.632) or anti-TPO auto-antibodies positivity (p=0.139) was found.
A case of thyrotropin (TSH)-secreting tumor complicated by periodic paralysis.
Thyrotropin releasing hormone (TRH) and metoclopramide testing in infertile women.
"Age-specific distribution of serum thyrotropin and antithyroid antibodies in the US population: implications for the prevalence of subclinical hypothyroidism", J Clin.
In the pathogenesis of Van Wyk-Grumbach syndrome, it was proposed primarily that low thyroid hormone levels caused to an increase in thyrotropin releasing hormone by disrupting negative feedback.
Effect of postoperative thyrotropin suppressive therapy on bone mineral density in patients with papillary thyroid carcinoma: a prospective controlled study.

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