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Osmoreceptor

December 12, 2023

An osmoreceptor is a sensory receptor primarily found in the hypothalamus of most homeothermic organisms that detects changes in osmotic pressure. Osmoreceptors can be found in several structures, including two of the circumventricular organs – the vascular organ of the lamina terminalis, and the subfornical organ. They contribute to osmoregulation, controlling fluid balance in the body.[1] Osmoreceptors are also found in the kidneys where they also modulate osmolality.

Mechanism of activation in humans edit

Osmoreceptors are located in two of the circumventricular organs — the vascular organ of lamina terminalis (VOLT) and the subfornical organ. These two circumventricular organs are located along the anteroventral region of the third ventricle, called the AV3V region.[2] Between these two organs is the median preoptic nucleus, which has multiple nerve connections with the two organs, as well as with the supraoptic nuclei and blood pressure control centers in the medulla oblongata.[2]

The osmoreceptors have a defined functionality as neurons that are endowed with the ability to detect extracellular fluid osmolarity. 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/L, 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+ and K+ ions to enter the cell.[3] 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 channels in the axon terminal. This leads to a Ca2+ 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 attached to the 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.[4]

Macula densa edit

The macula densa region of the kidney's juxtaglomerular apparatus is another modulator of blood osmolality.[5] The macula densa responds to changes in osmotic pressure through changes in the rate of sodium ion (Na+) flow through the nephron. Decreased Na+ 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. This is commonly known as the renin-angiotensin-aldosterone system.

See also edit

References edit

  1. ^ Bourque CW (July 2008). "Central mechanisms of osmosensation and systemic osmoregulation". Nature Reviews. Neuroscience. 9 (7): 519–31. doi:10.1038/nrn2400. PMID 18509340. S2CID 205504313.
  2. ^ a b Hall, John E. (2021). Guyton and Hall textbook of medical physiology. Michael E. Hall (14 ed.). Philadelphia, PA. p. 376. ISBN 978-0-323-59712-8. OCLC 1129099861.{{cite book}}: CS1 maint: location missing publisher (link)
  3. ^ Binder MD, Hirokawa N, Windhorst U, eds. (2009). "Stretch-inactivated Cation Channel (SIC)". Encyclopedia of Neuroscience. Berlin Heidelberg: Springer. pp. 3865. doi:10.1007/978-3-540-29678-2_5688. ISBN 978-3-540-23735-8.
  4. ^ Turner NN, Lameire N, Goldsmith DJ, Winearls CG, Himmelfarb J, Remuzzi G, Bennet WG, Broe ME, Chapman JR, Covic A, Jha V, Sheerin N, Unwin R, Woolf A, eds. (2015-10-29). Oxford Textbook of Clinical Nephrology (Fourth ed.). Oxford, New York: Oxford University Press. ISBN 978-0-19-959254-8.
  5. ^ "The Urinary System". www2.highlands.edu.

External links edit

  • theFreeDictionary-osmoreceptor

December 12, 2023
osmoreceptor, osmoreceptor, sensory, receptor, primarily, found, hypothalamus, most, homeothermic, organisms, that, detects, changes, osmotic, pressure, found, several, structures, including, circumventricular, organs, vascular, organ, lamina, terminalis, subf. An osmoreceptor is a sensory receptor primarily found in the hypothalamus of most homeothermic organisms that detects changes in osmotic pressure Osmoreceptors can be found in several structures including two of the circumventricular organs the vascular organ of the lamina terminalis and the subfornical organ They contribute to osmoregulation controlling fluid balance in the body 1 Osmoreceptors are also found in the kidneys where they also modulate osmolality Contents 1 Mechanism of activation in humans 2 Macula densa 3 See also 4 References 5 External linksMechanism of activation in humans editOsmoreceptors are located in two of the circumventricular organs the vascular organ of lamina terminalis VOLT and the subfornical organ These two circumventricular organs are located along the anteroventral region of the third ventricle called the AV3V region 2 Between these two organs is the median preoptic nucleus which has multiple nerve connections with the two organs as well as with the supraoptic nuclei and blood pressure control centers in the medulla oblongata 2 The osmoreceptors have a defined functionality as neurons that are endowed with the ability to detect extracellular fluid osmolarity 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 L 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 and K ions to enter the cell 3 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 channels in the axon terminal This leads to a Ca2 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 attached to the 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 4 Macula densa editThe macula densa region of the kidney s juxtaglomerular apparatus is another modulator of blood osmolality 5 The macula densa responds to changes in osmotic pressure through changes in the rate of sodium ion Na flow through the nephron Decreased Na 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 This is commonly known as the renin angiotensin aldosterone system See also editHypothalamus Vasopressin BaroreceptorsReferences edit Bourque CW July 2008 Central mechanisms of osmosensation and systemic osmoregulation Nature Reviews Neuroscience 9 7 519 31 doi 10 1038 nrn2400 PMID 18509340 S2CID 205504313 a b Hall John E 2021 Guyton and Hall textbook of medical physiology Michael E Hall 14 ed Philadelphia PA p 376 ISBN 978 0 323 59712 8 OCLC 1129099861 a href Template Cite book html title Template Cite book cite book a CS1 maint location missing publisher link Binder MD Hirokawa N Windhorst U eds 2009 Stretch inactivated Cation Channel SIC Encyclopedia of Neuroscience Berlin Heidelberg Springer pp 3865 doi 10 1007 978 3 540 29678 2 5688 ISBN 978 3 540 23735 8 Turner NN Lameire N Goldsmith DJ Winearls CG Himmelfarb J Remuzzi G Bennet WG Broe ME Chapman JR Covic A Jha V Sheerin N Unwin R Woolf A eds 2015 10 29 Oxford Textbook of Clinical Nephrology Fourth ed Oxford New York Oxford University Press ISBN 978 0 19 959254 8 The Urinary System www2 highlands edu External links edittheFreeDictionary osmoreceptor Retrieved from https en wikipedia org w index php title Osmoreceptor amp oldid 1188310514, wikipedia, wiki, book, books, library,

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