Editing Endocrine system (section)

==Function==
{{See also|List of human endocrine organs and actions}}

===Hormones===
{{Main|Hormone}}
A [[hormone]] is any of a class of [[cell signalling|signaling molecules]] produced by cells in [[gland]]s in [[multicellular organism]]s that are transported by the [[circulatory system]] to target distant organs to regulate [[physiology]] and [[behaviour]]. Hormones have diverse chemical structures, mainly of 3 classes: [[eicosanoid]]s, [[steroid]]s, and [[amino acid]]/[[protein]] derivatives ([[amine]]s, [[peptide]]s, and [[protein]]s). The glands that secrete hormones comprise the endocrine system. The term hormone is sometimes extended to include chemicals produced by cells that affect the same cell ([[autocrine signaling|autocrine]] or [[intracrine|intracrine signalling]]) or nearby cells ([[paracrine signalling]]).

Hormones are used to communicate between [[organ (anatomy)|organs]] and tissues for [[physiological]] regulation and [[behavioral]] activities, such as digestion, [[metabolism]], [[respiration (physiology)|respiration]], [[tissue (biology)|tissue]] function, [[sensory perception]], [[sleep]], [[excretion]], [[lactation]], [[Stress (physiology)|stress]], [[human development (biology)|growth and development]], [[Motor coordination|movement]], [[reproduction]], and [[mood (psychology)|mood]].<ref>{{cite book |author=Neave N |title=Hormones and behaviour: a psychological approach |year=2008 |publisher=Cambridge Univ. Press |location=Cambridge |isbn=978-0-521-69201-4}}
* {{cite journal |author=Claire L. Gibson |title=Hormones and Behaviour: A Psychological Approach |journal=Perspectives in Biology and Medicine |type=Review |volume=53 |issue=1 |pages=152–155 |date=Winter 2010 |doi=10.1353/pbm.0.0141 |s2cid=72100830 |url=http://muse.jhu.edu/journals/pbm/summary/v053/53.1.gibson.html}}</ref><ref>{{cite web |title=Hormones |url=https://www.nlm.nih.gov/medlineplus/hormones.html |website=MedlinePlus |publisher=U.S. National Library of Medicine}}</ref>

Hormones affect distant cells by binding to specific [[receptor (biochemistry)|receptor]] proteins in the target cell resulting in a change in cell function. This may lead to cell type-specific responses that include rapid changes to the activity of existing proteins, or slower changes in the [[gene expression|expression]] of target genes. Amino acid–based hormones ([[amines]] and [[peptide hormone|peptide or protein hormones]]) are water-soluble and act on the surface of target cells via [[signal transduction]] pathways; [[steroid hormone]]s, being lipid-soluble, move through the [[plasma membrane]]s of target cells to act within their [[cell nucleus|nuclei]].

===Cell signalling===
The typical mode of [[cell signalling]] in the endocrine system is endocrine signaling, that is, using the circulatory system to reach distant target organs. However, there are also other modes, i.e., paracrine, autocrine, and [[neuroendocrine]] signaling. Purely neurocrine signaling between [[neurons]], on the other hand, belongs completely to the [[nervous system]].

====Autocrine====
{{Main|Autocrine signalling}}
Autocrine signaling is a form of signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on the same cell, leading to changes in the cells.

====Paracrine====
{{Main|Paracrine signalling}}
Some endocrinologists and clinicians include the paracrine system as part of the endocrine system, but there is not consensus. Paracrines are slower acting, targeting cells in the same tissue or organ. An example of this is [[somatostatin]] which is released by some pancreatic cells and targets other pancreatic cells.<ref name="Marieb" />

====Juxtacrine====
{{Main|Juxtacrine signalling}}
[[Juxtacrine signalling|Juxtacrine]] signaling is a type of intercellular communication that is transmitted via oligosaccharide, lipid, or protein components of a cell membrane, and may affect either the emitting cell or the immediately adjacent cells.<ref>{{Cite book |vauthors=Gilbert F |date=2000 |chapter=Juxtacrine Signaling |title=Developmental Biology |edition=6th |location=Sunderland, MA |publisher=Sinauer Associates |isbn=0-87893-243-7 |url=https://www.ncbi.nlm.nih.gov/books/NBK10072/ |language=en}}</ref>

It occurs between adjacent cells that possess broad patches of closely opposed plasma membrane linked by transmembrane channels known as [[connexon]]s. The gap between the cells can usually be between only 2 and 4&nbsp;nm.<ref name=":0">{{cite book |title=Vander's Human Physiology: the mechanisms of body function |last=Vander |first=Arthur |name-list-style=vanc |publisher=McGraw-Hill Higher Education |year=2008 |isbn=978-0-07-304962-5 |location=Boston |pages=[https://archive.org/details/isbn_9780071283663/page/332 332–333] |url=https://archive.org/details/isbn_9780071283663/page/332}}</ref>