thyroxine /thy·rox·ine/ (T4) (thi-rok´sin) an iodine-containing hormone secreted by the thyroid gland, occurring naturally as l-thyroxine; its chief function is to increase the rate of cell metabolism. It is deiodinated in peripheral tissues to form triiodothyronine, which has greater biological activity. A preparation of thyroxine, levothyroxine, is used pharmaceutically.
Thyroxine (T 4 )
thyroxine (T4)
thyroxine (thīrok´sin),
thyroxine
thy·rox·ine (th -r k s n , -s n) or thy·rox·in (-rksn)n. Abbr. T4 An iodine-containing hormone that is produced by the thyroid gland, increases the rate of cell metabolism, regulates growth, and is made synthetically for treatment of thyroid disorders. |
Thyroxine (T 4 )
Thyroid hormone that regulates many essential body processes.
Mentioned in: Hypothyroidism
thyroxine (T4)
[thīrok′sēn]
a hormone of the thyroid gland, derived from tyrosine and deiodinated in the periphery to T3 (triiodothyronine) that stimulates metabolic rate. Also called tetraiodothyronine.
thyroxine (thīrok´sin),
n the hormone secretion of the thyroid gland, L-3,5,3´,5´-tetraiodothyronine.
thyroxine, thyroxin
a hormone of the thyroid gland that contains iodine and is a derivative of the amino acid tyrosine. The chemical name for thyroxine is tetraiodothyronine (symbol, T4); it is formed and stored in the thyroid follicles as thyroglobulin, the storage form. Thyroxine is released from the gland by the action of a proteolytic enzyme. T4 is deiodinated in peripheral tissues to form tri-iodothyronine (T3), which has a greater biological activity.
Thyroxine acts as a catalyst in the body and influences a great variety of effects, including metabolic rate (oxygen consumption); growth and development; metabolism of carbohydrates, fats, proteins, electrolytes and water; vitamin requirements; reproduction; and resistance to infection.
Thyroxine can be extracted from animals or made synthetically; it is used in the treatment of hypothyroidism and some types of goiter.
free thyroxine
the metabolically active fraction of thyroxine; abbreviated FT4, Tf. T4 = Tf + TBG. The amount is very small and difficult to estimate so that the amount present in serum is not used as a more accurate indicator of thyroxine status than T4.
thyroxine-binding globulin (TBG)
most (99.95%) of the thyroxine in plasma is bound to globulin and a small amount bound to prealbumin.
thyroxine-binding prealbumin
bound to a small fraction of circulating T4. This is the only known function of prealbumins.
L-thyroxine
see levothyroxine.
thyroxine
T4, 3,5,3',5'-Tetraiodothyronine A hormone that stimulates metabolism and O2 consumption, which is secreted by the thyroid gland in response to TSH–thyrotropin produced in the
adenohypophysis–anterior pituitary gland ↑ in Hyperthyroidism, acute thyroiditis, myasthenia gravis, preeclampsia, pregnancy, viral hepatitis, therapy with clofibrate, OCs, estrogens, perphenazine ↓ in Hypothyroidism, malnutrition,
vigorous exercise, hypofunction of adenohypophysis–anterior pituitary gland, renal failure, therapy with corticosteroids, chlorpromazine, heparin, lithium, phenytoin, propranolol, reserpine, salicylates, sulfonamides, testosterone,
tolbutamide. See Triiodothyronine–T3, Thyroxine-binding globulin.
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