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[[File:1802 Examples of Amine Peptide Protein and Steroid Hormone Structure.jpg|thumb|00px|Različiti tipovi hormona se luče u telu. Oni imaju različite biološke uloge i funkcije.]]
[[Datoteka:Adrenaline_chemical_structure.png|thumb|Strukturna formula hormona [[Epinefrin|adrenalina]], jednog od [[kateholamin]]a]]
'''Hormon''' (od [[Grčki jezik|Grčkog]] ''όρμή'' - pokrenuti, probuditi) je [[hemijsko jedinjenje|hemijski]] glasnik između [[ćelija (biologija)|ćelija]] (ili grupe ćelija). To su organska jedinjenja različite hemijske prirode, koja deluju u malim količinama. Njihovo delovanje je specifično pa nedostatak dovodi do karakterističnih promena u organizmu. Svi [[višećelijski organizmi]] organizmi proizvode hormone (uključujući biljke - fitohormoni).
 
U cilju brzog oslobađanja aktivnih hormona u [[Cirkulatorni sistem|krvotok]], ćelije biosintetičkih hormona mogu proizvoditi i čuvati biološke neaktivne hormone u vidu pre- ili prohormona. Ovi potom mogu brzo biti, kao rezultat odgovarajućih stimulansa, konvertovani u svoje aktivne forme hormona.
 
== Regulation ==
 
The rate of hormone biosynthesis and secretion is often regulated by a [[Homeostasis|homeostatic]] [[negative feedback]] control mechanism. Such a mechanism depends on factors that influence the [[metabolism]] and [[excretion]] of hormones. Thus, higher hormone concentration alone cannot trigger the negative feedback mechanism. Negative feedback must be triggered by overproduction of an "effect" of the hormone.
 
Hormone secretion can be stimulated and inhibited by:
* Other hormones (''stimulating''- or ''releasing'' -hormones)
* Plasma concentrations of ions or nutrients, as well as binding [[globulin]]s
* [[Neuron]]s and mental activity
* Environmental changes, e.g., of light or temperature
 
One special group of hormones is the [[tropic hormone]]s that stimulate the hormone production of other [[endocrine system|endocrine glands]]. For example, [[thyroid-stimulating hormone]] (TSH) causes growth and increased activity of another endocrine gland, the [[thyroid]], which increases output of [[thyroid hormone]]s.
 
To release active hormones quickly into the [[Circulatory system|circulation]], hormone biosynthetic cells may produce and store biologically inactive hormones in the form of [[prehormone|pre-]] or [[prohormone]]s. These can then be quickly converted into their active hormone form in response to a particular stimulus.
 
[[Eicosanoids]] are considered to act as local hormones.
 
== Receptori ==
[[File:Steroid and Lipid Hormones.svg|thumb|400px|The left diagram shows a steroid (lipid) hormone (1) entering a cell and (2) binding to a receptor protein in the nucleus, causing (3) mRNA synthesis which is the first step of protein synthesis. The right side shows protein hormones (1) binding with receptors which (2) begins a transduction pathway. The transduction pathway ends (3) with transcription factors being activated in the nucleus, and protein synthesis beginning. In both diagrams, a is the hormone, b is the cell membrane, c is the cytoplasm, and d is the nucleus.]]
 
Most hormones initiate a cellular response by initially binding to either [[membrane protein|cell membrane associated]] or [[intracellular]] [[receptor (biochemistry)|receptor]]s. A cell may have several different receptor types that recognize the same hormone but activate different [[signal transduction]] pathways, or a cell may have several different receptors that recognize different hormones and activate the same biochemical pathway.
 
Receptors for most [[peptide hormone|peptide]] as well as many [[eicosanoid]] hormones are embedded in the [[plasma membrane]] at the surface of the cell and the majority of these receptors belong to the [[G protein-coupled receptor]] (GPCR) class of seven [[alpha helix]] [[transmembrane]] proteins. The interaction of hormone and receptor typically triggers a cascade of secondary effects within the [[cytoplasm]] of the cell, often involving [[phosphorylation]] or dephosphorylation of various other cytoplasmic proteins, changes in [[ion channel]] permeability, or increased concentrations of intracellular molecules that may act as [[second messenger|secondary messengers]] (e.g., [[cyclic AMP]]). Some [[protein hormone]]s also interact with [[intracellular]] receptors located in the [[cytoplasm]] or [[Cell nucleus|nucleus]] by an [[intracrine]] mechanism.
 
For [[steroid hormone|steroid]] or [[thyroid hormone|thyroid]] hormones, their [[steroid hormone receptor|receptors]] are located [[intracellular|inside the cell]] within the [[cytoplasm]] of the target cell. These receptors belong to the [[nuclear receptor]] family of ligand-activated [[transcription factor]]s. To bind their receptors, these hormones must first cross the cell membrane. They can do so because they are lipid-soluble. The combined hormone-receptor [[protein complex|complex]] then moves across the nuclear membrane into the nucleus of the cell, where it binds to specific [[DNA sequences]], regulating the expression of certain [[genes]], and thereby increasing the levels of the proteins encoded by these genes.<ref name=beato>{{cite journal | author =Beato M, Chavez S and Truss M | title = Transcriptional regulation by steroid hormones | journal = Steroids | year=1996 | volume=61 | issue=4 | pages=240–251 | pmid = 8733009 | doi = 10.1016/0039-128X(96)00030-X}}</ref> However, it has been shown that not all steroid receptors are located inside the cell. Some are associated with the [[plasma membrane]].<ref name=hammes>{{cite journal | author =Hammes SR | title = The further redefining of steroid-mediated signaling | journal = Proc Natl Acad Sci USA | year=2003 | volume=100 | issue=5 | pages=21680–2170 | pmid = 12606724 | doi = 10.1073/pnas.0530224100 | pmc =151311}}</ref>
 
== Hormonski efekti ==
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