Editing Endocrinology (section)

==The endocrine system==
{{Main|Endocrine system}} Endocrinology is the study of the endocrine system in the [[human body]].<ref>{{cite web | title = Endocrinology, Diabetes and Metabolism Specialty Description | publisher = American Medical Association | url = https://www.ama-assn.org/specialty/endocrinology-diabetes-and-metabolism-specialty-description | access-date = 14 September 2020}}</ref> This is a system of [[gland]]s which secrete hormones. Hormones are chemicals that affect the actions of different organ systems in the body. Examples include [[thyroid hormone]], [[growth hormone]], and [[insulin]]. The endocrine system involves a number of feedback mechanisms, so that often one hormone (such as [[Thyroid-stimulating hormone|thyroid stimulating hormone]]) will control the action or release of another secondary hormone (such as [[thyroid hormone]]). If there is too much of the secondary hormone, it may provide negative feedback to the primary hormone, maintaining [[homeostasis]].<ref>{{Citation |last=Carroll |first=Robert G. |title=13 - Endocrine System |date=2007-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780323043182500194 |work=Elsevier's Integrated Physiology |pages=157–176 |editor-last=Carroll |editor-first=Robert G. |access-date=2023-11-15 |place=Philadelphia |publisher=Mosby |isbn=978-0-323-04318-2}}</ref><ref>{{Cite journal |last1=Molnar |first1=Charles |last2=Gair |first2=Jane |date=2015-05-14 |title=11.4 Endocrine System |url=https://opentextbc.ca/biology/chapter/11-4-endocrine-system/ |language=en}}</ref><ref>{{Cite web |title=How the Pill Works {{!}} American Experience {{!}} PBS |url=https://www.pbs.org/wgbh/americanexperience/features/pill-how-pill-works/ |access-date=2023-11-15 |website=www.pbs.org |language=en}}</ref>

In the original 1902 definition by Bayliss and Starling (see below), they specified that, to be classified as a hormone, a chemical must be produced by an organ, be released (in small amounts) into the blood, and be transported by the blood to a distant organ to exert its specific function. This definition holds for most "classical" hormones, but there are also [[paracrine]] mechanisms (chemical communication between cells within a tissue or organ), [[autocrine signaling|autocrine]] signals (a chemical that acts on the same cell), and [[intracrine]] signals (a chemical that acts within the same cell).<ref>{{cite book |author=Nussey S|author2=Whitehead S |title=Endocrinology: An Integrated Approach  |date=2001 |isbn=978-1-85996-252-7 |publisher=Bios Scientific Publ. |location=Oxford}}</ref> A [[neuroendocrine]] signal is a "classical" hormone that is released into the blood by a neurosecretory neuron (see article on [[neuroendocrinology]]).{{cn|date=March 2024}}

=== Hormones ===
Griffin and Ojeda identify three different classes of hormones based on their chemical composition:<ref>{{cite book |author=Ojeda, Sergio R.|author2=Griffin, James Bennett |title=Textbook of endocrine physiology |url=https://archive.org/details/textbookofendocr00oxfo|url-access=registration|publisher=Oxford University Press |location=Oxford [Oxfordshire] |date=2000 |edition=4th |isbn=978-0-19-513541-1 }}</ref>

====Amines====
{{multiple image
| footer = Examples of '''amine hormones'''
| total_width = 270
| image1 = Norepinephrine structure with descriptor.svg
| caption1 = [[Norepinephrine]]
| image2 = Triiodothyronine.svg
| caption2 = [[Triiodothyronine]]
}}
Amines, such as [[norepinephrine]], [[epinephrine]], and [[dopamine]] ([[catecholamines]]), are derived from single [[amino acid]]s, in this case tyrosine. [[Thyroid]] hormones such as [[Triiodothyronine|3,5,3'-triiodothyronine]] (T3) and [[Levothyroxine|3,5,3',5'-tetraiodothyronine]] (thyroxine, T4) make up a subset of this class because they derive from the combination of two iodinated tyrosine amino acid residues.<ref>{{Cite journal |last1=Carvalho |first1=Denise P. |last2=Dupuy |first2=Corinne |date=2017-12-15 |title=Thyroid hormone biosynthesis and release |url=https://www.sciencedirect.com/science/article/pii/S0303720717300515 |journal=Molecular and Cellular Endocrinology |series=A century of thyroid hormone research - Vol. I: The expanded thyroid hormone network: novel metabolites and modes of action |volume=458 |pages=6–15 |doi=10.1016/j.mce.2017.01.038 |pmid=28153798 |s2cid=31150531 |issn=0303-7207}}</ref>

====Peptide and protein====
[[Peptide hormones]] and protein hormones consist of three (in the case of [[thyrotropin-releasing hormone]]) to more than 200 (in the case of [[follicle-stimulating hormone]]) amino acid residues and can have a molecular mass as large as 31,000 grams per mole. All hormones secreted by the pituitary gland are peptide hormones, as are [[leptin]] from adipocytes, [[ghrelin]] from the stomach, and [[insulin]] from the [[pancreas]].{{cn|date=May 2022}}

====Steroid====
{{multiple image
| footer = Examples of '''steroid hormones'''
| total_width = 270
| image1 = Cortisol2.svg
| caption1 = [[Cortisol]]
| image2 = Cholecalciferol.svg
| caption2 = [[Cholecalciferol|Vitamin D<sub>3</sub>]]
}}
[[Steroid hormones]] are converted from their parent compound, [[cholesterol]]. [[Mammal]]ian steroid hormones can be grouped into five groups by the receptors to which they bind: [[glucocorticoid]]s, [[mineralocorticoid]]s, [[androgen]]s, [[estrogen]]s, and [[progestogen]]s. Some forms of [[vitamin D]], such as [[calcitriol]], are steroid-like and bind to homologous receptors, but lack the characteristic fused ring structure of true steroids.