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T 3 is the more metabolically active hormone produced from T 4.T 4 is deiodinated by three deiodinase enzymes to produce the more-active triiodothyronine: . Type I present in liver, kidney, thyroid, and (to a lesser extent) pituitary; it accounts for 80% of the deiodination of T 4.
Low-T3 syndrome and high-T3 syndrome: Consequences of step-up hypodeiodination, e.g. in critical illness as an example for type 1 allostasis, or hyperdeiodination, as in type 2 allostasis, including posttraumatic stress disorder. Resistance to thyroid hormone: Feedback loop interrupted on the level of pituitary thyroid hormone receptors.
The major form of thyroid hormone in the blood is thyroxine (T 4), whose half-life of around one week is longer than that of T 3. In humans, the ratio of T 4 to T 3 released into the blood is approximately 14:1. T 4 is converted to the active T 3 (three to four times more potent than T 4) within cells by deiodinases (5′-deiodinase).
Euthyroid sick syndrome. Euthyroid sick syndrome ( ESS) is a state of adaptation or dysregulation of thyrotropic feedback control [1] wherein the levels of T3 and/or T4 are abnormal, but the thyroid gland does not appear to be dysfunctional. This condition may result from allostatic responses of hypothalamus-pituitary-thyroid feedback control ...
The main diagnostic sign is an oral body temperature that averages well below 37.0 °C (98.6 °F). This overlaps with normal body temperature, which is usually within the range of 36.5–37.5 °C (97.7–99.5 °F). Wilson says that his diagnosis is confirmed if the patient responds to treatment with slow-release T3 (SR-T3).
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Intuitively, if plasma levels of T3 fall, there would be a compensatory rise in TSH, the secretion of which is inhibited by T3. However, because type 2 deiodinase mediates the conversion of T4 to T3 within the pituitary and CNS, and because caloric restriction does not affect this enzyme, local T3 levels in the pituitary are normal.Thus, the ...
Iodothyronine deiodinases ( EC 1.21.99.4 and EC 1.21.99.3) are a subfamily of deiodinase enzymes important in the activation and deactivation of thyroid hormones. Thyroxine (T 4 ), the precursor of 3,5,3'- triiodothyronine (T 3) is transformed into T 3 by deiodinase activity. T 3, through binding a nuclear thyroid hormone receptor, influences ...