Osmoreseptor: Perbezaan antara semakan
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'''Osmoreseptor''' merupakan [[penerima deria]] terutamanya dijumpai dalam [[hipotalamus]] pada kebanyakan organisma [[homeoterm]]ik yang mengesan perubahan [[tekanan osmosis]]. Osmoreceptors boleh didapati dalam beberapa struktur, termasuk dua daripada [[organ-organ lengan]] – [[organ vaskular lamina terminalis]], dan [[organ subfon]]. Mereka menyumbang kepada [[osmoregulasi]], mengawal [[imbangan cecair]] dalam badan.<ref name="Bourque">{{cite journal | vauthors = Bourque CW | title = Central mechanisms of osmosensation and systemic osmoregulation | journal = Nature Reviews. Neuroscience | volume = 9 | issue = 7 | pages = 519–31 | date = July 2008 | pmid = 18509340 | doi = 10.1038/nrn2400 }}</ref> Osmoreseptor juga dijumpai di [[buah pinggang]] di mana mereka juga memodulasi [[Kemolalan#keosmolalan|keosmolalan]].
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==Mechanism of activation in humans==
Osmoreceptors are located in the [[vascular organ of lamina terminalis]] (VOLT) a [[circumventricular organ]] which lacks a blood-brain barrier. They have a defined functionality as neurons that are endowed with the ability to detect extracellular fluid [[osmolarity]]. The VOLT is strongly interconnected with the [[median preoptic nucleus]], and together these structures comprise the [[Anteroventral periventricular nucleus|anteroventral third ventricle region]].<ref>{{cite journal | vauthors = Verbalis JG | title = How does the brain sense osmolality? | journal = Journal of the American Society of Nephrology | volume = 18 | issue = 12 | pages = 3056–9 | date = December 2007 | pmid = 18003769 | doi = 10.1681/ASN.2007070825 }}</ref> Osmoreceptors have [[aquaporin 4]] proteins spanning through their plasma membranes in which water can diffuse, from an area of high to low water concentration. If plasma osmolarity rises above 290 mOsmol/kg, then water will move out of the cell due to osmosis, causing the neuroreceptor to shrink in size. Embedded into the cell membrane are [[stretch inactivated cation channels]] (SICs), which when the cell shrinks in size, open and allow positively charged ions, such as Na<sup>+</sup> and K<sup>+</sup> ions to enter the cell.<ref>{{cite book | url = https://link.springer.com/referenceworkentry/10.1007/978-3-540-29678-2_5688 | title = Encyclopedia of Neuroscience | date = 2009 | publisher = Springer | location = Berlin Heidelberg | isbn = 978-3-540-23735-8 |pages=3865–3865|doi=10.1007/978-3-540-29678-2_5688 | editor-last=Binder | editor-first = Marc D. |editor-last2=Hirokawa|editor-first2=Nobutaka|editor-last3=Windhorst|editor-first3=Uwe | name-list-format = vanc }}</ref> This causes initial depolarisation of the osmoreceptor and activates [[voltage-gated sodium channel]], which through a complex conformational change, allows more sodium ions to enter the neuron, leading to further depolarisation and an [[action potential]] to be generated. This action potential travels along the axon of the neuron, and causes the opening of [[voltage-dependent calcium channel]]<nowiki/>s in the axon terminal. This leads to a Ca<sup>2+</sup> influx, due to calcium ions diffusing into the neuron along their [[electrochemical gradient]]. The calcium ions binds to the [[synaptotagmin 1]] sub-unit of the [[SNARE (protein)|SNARE protein]] attached to the [[Vasopressin|arginine-vasopressin]] (AVP) containing vesicle membrane. This causes the fusion of the vesicle with the neuronal post synaptic membrane. Subsequent release of AVP into the posterior pituitary gland occurs, whereby vasopressin is secreted into the blood stream of the nearby capillaries.<ref>{{cite book | url = https://global.oup.com/academic/product/oxford-textbook-of-clinical-nephrology-9780199592548?cc=gb&lang=en& | title=Oxford Textbook of Clinical Nephrology|date=2015-10-29|publisher=Oxford University Press | isbn = 978-0-19-959254-8 | edition=Fourth|series=Oxford Textbook|location=Oxford, New York | editor-first1 = Neil N. | editor-last1 = Turner | editor-first2 = Norbert | editor-last2 = Lameire | editor-first3 = David J. | editor-last3 = Goldsmith | editor-first4 = Christopher G. | editor-last4 = Winearls | editor-first5 = Jonathan | editor-last5 = Himmelfarb | editor-first6 = Giuseppe | editor-last6 = Remuzzi | editor-first7 = William G. | editor-last7 = Bennet | editor-first8 = Mark E. de | editor-last8 = Broe | editor-first9 = Jeremy R. | editor-last9 = Chapman | editor-first10 = Adrian | editor-last10 = Covic | editor-first11 = Vivekanad | editor-last11 = Jha | editor-first12 = Neil | editor-last12 = Sheerin | editor-first13 = Robert | editor-last13 = Unwin | editor-first14 = Adrian | editor-last14 = Woolf | name-list-format = vanc }}</ref>
==Macula densa==
The [[macula densa]] region of the kidney's [[juxtaglomerular apparatus]] is another modulator of blood [[Molality#Osmolality|osmolality]].<ref name="highlands">{{cite web|title=The Urinary System|url=http://www2.highlands.edu/academics/divisions/scipe/biology/faculty/harnden/2122/notes/urinary.htm|website=www2.highlands.edu}}</ref> The macula densa responds to changes in osmotic pressure through changes in the rate of [[Sodium |sodium ion]] (Na<sup>+</sup>) flow through the [[nephron]]. Decreased Na<sup>+</sup> flow stimulates [[tubuloglomerular feedback]] to autoregulate, a signal (thought to be regulated by [[adenosine]]) sent to the nearby [[juxtaglomerular cells]] of the [[afferent arteriole]], causing the juxtaglomerular cells to release the [[protease]] [[renin]] into circulation. Renin cleaves the [[zymogen]] [[angiotensinogen]], always present in plasma as a result of constitutive production in the liver, into a second inactive form, [[angiotensin I]], which is then converted to its active form, [[angiotensin II]], by [[angiotensin converting enzyme]] (ACE), which is widely distributed in the small vessels of the body, but particularly concentrated in the pulmonary capillaries of the lungs. [[Angiotensin II]] exerts system wide effects, triggering [[aldosterone]] release from the [[adrenal cortex]], direct [[vasoconstriction]], and [[thirst]] behaviors originating in the [[hypothalamus]].
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== Lihat juga ==
* [[Hipotalamus]]
* [[Vasopresin]]
* [[Baroreseptor]]
== Rujukan ==
<references responsive/>
== Pautan luar ==
* [http://medical-dictionary.thefreedictionary.com/osmoreceptor ''theFreeDictionary-osmoreceptor'']
{{tunas-biologi}}
[[Kategori:Penerima deria]]
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