Editing Homeostasis (section)

{{Short description|State of steady internal conditions maintained by living things}}
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In [[biology]], '''homeostasis''' ([[British English|British]] also '''homoeostasis'''; {{IPAc-en |h |ɒ |m |i |əʊ |ˈ |s |t |eɪ |s |ɪ |s |,_ |- |m |i |ə |-}} {{respell|hoh|mee|oh|STAY|sis}}) is the state of steady internal [[physics|physical]] and [[chemistry|chemical]] conditions maintained by [[organism|living systems]].<ref>{{Cite book |title=Anatomy and physiology |last=Gordon |first=Betts, J. |others=DeSaix, Peter., Johnson, Eddie., Johnson, Jody E., Korol, Oksana., Kruse, Dean H., Poe, Brandon. |isbn=978-1-947172-04-3 |location=Houston, Texas |page=9 |oclc=1001472383}}</ref> This is the condition of optimal functioning for the organism and includes many variables, such as [[body temperature]] and [[fluid balance]], being kept within certain pre-set limits (homeostatic range). Other variables include the [[pH]] of [[extracellular fluid]], the concentrations of [[sodium]], [[potassium]], and [[calcium]] [[ion]]s, as well as the [[blood sugar level]], and these need to be regulated despite changes in the environment, diet, or level of activity. Each of these variables is controlled by one or more regulators or homeostatic mechanisms, which together maintain life.

Homeostasis is brought about by a natural resistance to change when already in optimal conditions,<ref name="EM">{{cite book |title=A dictionary of biology |last=Martin |first=Elizabeth |date=2008 |publisher=Oxford University Press |isbn=978-0-19-920462-5 |edition=6th |location=Oxford |pages=315–316}}</ref> and equilibrium is maintained by many regulatory mechanisms; it is thought to be the central motivation for all organic action. All homeostatic control mechanisms have at least three interdependent components for the variable being regulated: a receptor, a control center, and an effector.<ref>{{cite web |title=Homeostasis  |url=https://www.biologyonline.com/dictionary/homeostasis  |website=Biology Online |date=27 October 2019  |access-date=27 October 2019  |archive-date=12 August 2020  |archive-url=https://web.archive.org/web/20200812025400/https://www.biologyonline.com/dictionary/homeostasis  |url-status=live }}</ref> The receptor is the sensing component that monitors and responds to changes in the environment, either external or internal. Receptors include [[thermoreceptor]]s and [[mechanoreceptor]]s. Control centers include the [[respiratory center]] and the [[renin–angiotensin system|renin-angiotensin system]]. An effector is the target acted on, to bring about the change back to the normal state. At the cellular level, effectors include [[nuclear receptor]]s that bring about changes in [[gene expression]] through up-regulation or down-regulation and act in [[negative feedback]] mechanisms. An example of this is in the control of [[bile acid]]s in the [[liver]].<ref name="Kalaany">{{cite journal |last1=Kalaany |first1=NY |last2=Mangelsdorf |first2=DJ |title=LXRS and FXR: the yin and yang of cholesterol and fat metabolism. |journal=Annual Review of Physiology |date=2006 |volume=68 |pages=159–91 |doi=10.1146/annurev.physiol.68.033104.152158 |pmid=16460270}}</ref>

Some centers, such as the [[renin–angiotensin system]], control more than one variable. When the receptor senses a stimulus, it reacts by sending action potentials to a control center. The control center sets the maintenance range—the acceptable upper and lower limits—for the particular variable, such as temperature. The control center responds to the signal by determining an appropriate response and sending signals to an [[Effector cell|effector]], which can be one or more muscles, an organ, or a [[gland]]. When the signal is received and acted on, negative feedback is provided to the receptor that stops the need for further signaling.<ref name=Marieb/>

The [[cannabinoid receptor type 1]], located at the [[Synapse|presynaptic]] [[neuron]], is a [[Receptor (biochemistry)|receptor]] that can stop stressful [[neurotransmitter]] release to the postsynaptic neuron; it is activated by [[Cannabinoid|endocannabinoids]] such as [[anandamide]] (''N''-arachidonoylethanolamide) and [[2-Arachidonoylglycerol|2-arachidonoylglycerol]] via a [[retrograde signaling]] process in which these compounds are synthesized by and released from postsynaptic neurons, and travel back to the presynaptic terminal to bind to the CB1 receptor for modulation of neurotransmitter release to obtain homeostasis.<ref>{{Citation |last=Lovinger |first=David M. |chapter=Presynaptic Modulation by Endocannabinoids |date=2008 |pages=435–477 |editor-last=Südhof |editor-first=Thomas C. |series=Handbook of Experimental Pharmacology |publisher=Springer Berlin Heidelberg  |doi=10.1007/978-3-540-74805-2_14 |pmid=18064422  |isbn=978-3-540-74805-2  |editor2-last=Starke |editor2-first=Klaus |title=Pharmacology of Neurotransmitter Release |volume=184  |issue=184}}</ref>

The [[polyunsaturated fatty acid]]s are [[lipid]] derivatives of [[Omega-3 fatty acid|omega-3]] ([[docosahexaenoic acid]], and [[eicosapentaenoic acid]]) or of [[Omega-6 fatty acid|omega-6]] ([[arachidonic acid]]). They are synthesized from [[Cell membrane|membrane]] [[phospholipid]]s and used as precursors for endocannabinoids to mediate significant effects in the fine-tuning adjustment of body homeostasis.<ref>{{Cite journal |last1=Freitas |first1=Hércules Rezende |last2=Isaac |first2=Alinny Rosendo |last3=Malcher-Lopes |first3=Renato |last4=Diaz |first4=Bruno Lourenço |last5=Trevenzoli |first5=Isis Hara |last6=Reis |first6=Ricardo Augusto De Melo |date=26 November 2018 |title=Polyunsaturated fatty acids and endocannabinoids in health and disease |journal=Nutritional Neuroscience |volume=21 |issue=10 |pages=695–714 |doi=10.1080/1028415X.2017.1347373 |pmid=28686542 |s2cid=40659630}}</ref>