File:Thyroid_system.upright=1.The<unk>  system of the<unk>  T3 and T4 rect 376 268 820 433<unk> -stimulating<unk> rect 411 200 849 266 Thyrotropin-releasing<unk> rect 297 168 502 200 Hypothalamus rect 66 216 386 256 Anterior pituitary gland rect 66 332 342 374 Negative feedback rect 308 436 510 475<unk>  gland rect 256 539 563 635<unk>  rect 357 827 569 856 Catecholamine rect 399 716 591 750 Metabolism desc bottom-left<unk>  are two<unk>  produced and released by the<unk>  gland, namely triiodothyronine (T3) and thyroxine (T4). They are tyrosine-based<unk>  that are primarily responsible for regulation of metabolism. T3 and T4 are partially composed of iodine. A deficiency of iodine leads to decreased production of T3 and T4, enlarges the<unk>  tissue and will cause the disease known as simple goitre. The major form of<unk> in the blood is thyroxine (T4), which has a longer half-life than T3. In humans, the ratio of T4 to T3 released into the blood is approximately 14:1. T4 is converted to the active T3 (three to four times more potent than T4) within cells by deiodinases (5′-deiodinase). These are further processed by decarboxylation and deiodination to produce iodothyronamine (T1a) and thyronamine (T0a). All three isoforms of the deiodinases are selenium-containing enzymes, thus dietary selenium is essential for T3 production. American chemist Edward Calvin Kendall was responsible for the isolation of thyroxine in 1915. In 2018, levothyroxine, a manufactured form of thyroxine, was the second most commonly prescribed medication in the United States, with more than 105million prescriptions. Levothyroxine is on the World Health Organization's List of Essential Medicines.
Thyroid hormones
Sex hormone
Gastrointestinal hormone
Hormone
Xenohormone
Thyroglobulin
Thyroid-stimulating hormone
Lipoprotein