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Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate. [ 1]
The hypothalamic–pituitary–thyroid axis ( HPT axis for short, a.k.a. thyroid homeostasis or thyrotropic feedback control) is part of the neuroendocrine system responsible for the regulation of metabolism and also responds to stress. As its name suggests, it depends upon the hypothalamus, the pituitary gland, and the thyroid gland .
The major form of thyroid hormone in the blood is thyroxine (T 4), whose half-life of around one week [4] is longer than that of T 3. [5] In humans, the ratio of T 4 to T 3 released into the blood is approximately 14:1. [6] T 4 is converted to the active T 3 (three to four times more potent than T 4) within cells by deiodinases (5′-deiodinase).
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 ...
Thyroid follicular cells form a simple cuboidal epithelium and are arranged in spherical thyroid follicles surrounding a fluid filled space known as the colloid. The interior space formed by the follicular cells is known as the follicular lumen. The basolateral membrane of follicular cells contains thyrotropin receptors which bind to thyroid ...
Iodothyronine deiodinase. 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 ...
A complete blood type would describe each of the 45 blood groups, and an individual's blood type is one of many possible combinations of blood-group antigens. [3] Almost always, an individual has the same blood group for life, but very rarely an individual's blood type changes through addition or suppression of an antigen in infection, malignancy, or autoimmune disease.
Thyroxine-binding globulin ( TBG) is a globulin protein that in humans is encoded by the SERPINA7 gene. TBG binds thyroid hormones in circulation. It is one of three transport proteins (along with transthyretin and serum albumin) responsible for carrying the thyroid hormones thyroxine (T 4) and triiodothyronine (T 3) in the bloodstream.