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Thyroid hormones

Thyroid-stimulating hormoneThyrotropin-releasing hormoneHypothalamusAnterior pituitary glandNegative feedbackThyroid glandThyroid hormonesCatecholamineMetabolism
The thyroid system of the thyroid hormones T3 and T4[1]

Thyroid hormones are any hormones produced and released by the thyroid gland, namely triiodothyronine (T3) and thyroxine (T4). They are tyrosine-based hormones that are primarily responsible for regulation of metabolism. T3 and T4 are partially composed of iodine, derived from food.[2] A deficiency of iodine leads to decreased production of T3 and T4, enlarges the thyroid tissue and will cause the disease known as simple goitre.[3]

The major form of thyroid hormone in the blood is thyroxine (T4), whose half-life of around one week[4] is longer than that of T3.[5] In humans, the ratio of T4 to T3 released into the blood is approximately 14:1.[6] 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.

The thyroid hormone is one of the factors responsible for the modulation of energy expenditure. This is achieved through several mechanisms, such as mitochondrial biogenesis, adaptive thermogenesis, etc.[7]

American chemist Edward Calvin Kendall was responsible for the isolation of thyroxine in 1915.[8] In 2020, levothyroxine, a manufactured form of thyroxine, was the second most commonly prescribed medication in the United States, with more than 98 million prescriptions.[9][10] Levothyroxine is on the World Health Organization's List of Essential Medicines.[11]

  1. ^ References used in image are found in image article in Commons:Commons:File:Thyroid system.png#References.
  2. ^ Sargis, Robert M. (21 October 2019). "How Your Thyroid Works". endocrineweb.com. Retrieved 20 May 2023.
  3. ^ Ijaz Ahsan (1997). Textbook of Surgery. CRC Press. p. 376. ISBN 9789057021398.
  4. ^ "How long does thyroxine stay in your system?". Drugs.com. Retrieved 6 August 2022.
  5. ^ Irizarry L (23 April 2014). "Thyroid Hormone Toxicity". Medscape. WedMD LLC. Retrieved 2 May 2014.
  6. ^ Pilo A, Iervasi G, Vitek F, Ferdeghini M, Cazzuola F, Bianchi R (April 1990). "Thyroidal and peripheral production of 3,5,3′-triiodothyronine in humans by multicompartmental analysis". The American Journal of Physiology. 258 (4 Pt 1): E715–E726. doi:10.1152/ajpendo.1990.258.4.E715. PMID 2333963.
  7. ^ Tran, Le Trung; Park, Sohee; Kim, Seul Ki; Lee, Jin Sun; Kim, Ki Woo; Kwon, Obin (April 2022). "Hypothalamic control of energy expenditure and thermogenesis". Experimental & Molecular Medicine. 54 (4): 358–369. doi:10.1038/s12276-022-00741-z. ISSN 2092-6413. PMC 9076616. PMID 35301430.
  8. ^ "1926 Edward C Kendall". American Society for Biochemistry and Molecular Biology. Archived from the original on 19 March 2012. Retrieved 4 July 2011.
  9. ^ "The Top 300 of 2020". ClinCalc. Retrieved 7 October 2022.
  10. ^ "Levothyroxine - Drug Usage Statistics". ClinCalc. Retrieved 7 October 2022.
  11. ^ World Health Organization (2019). World Health Organization model list of essential medicines: 21st list 2019. Geneva: World Health Organization. hdl:10665/325771. WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO.

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