Editing Rete mirabile

{{Short description|Complex of arteries and veins lying very close to each other}}
{{Infobox anatomy
| Name        = Rete mirabile
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| Caption     = Rete mirabile of a sheep
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A '''rete mirabile''' ([[Latin]] for "wonderful net"; {{plural form}}: '''retia mirabilia''') is a complex of [[artery|arteries]] and [[vein]]s lying very close to each other, found in some [[vertebrate]]s, mainly [[warm-blooded]] ones. The rete mirabile utilizes countercurrent blood flow within the net (blood flowing in opposite directions) to act as a [[countercurrent exchange]]r. It exchanges [[heat]], [[ion]]s, or [[gas]]es between vessel walls so that the two bloodstreams within the rete maintain a gradient with respect to [[temperature]], or concentration of gases or [[solutes]]. This term was coined by [[Galen]].<ref name="Mark Grant 2000">{{cite book | first = Mark | last = Grant | date = 2000 | title = Galen on Food and Diet | publisher = Routledge }}</ref><ref>{{cite web | title = Rete Mirabile | website = encyclopedia2.thefreedictionary.com | url = http://encyclopedia2.thefreedictionary.com/Rete+Mirabile | access-date = 6 September 2012}}</ref>

== Effectiveness ==
The effectiveness of retia is primarily determined by how readily the heat, ions, or gases can be exchanged.  For a given length, they are most effective with respect to gases or heat, then small ions, and decreasingly so with respect to other substances.{{cn|date=November 2021}}

The retia can provide for extremely efficient exchanges.  In [[bluefin tuna]], for example, nearly all of the metabolic heat in the venous blood is transferred to the arterial blood, thus conserving muscle temperature; that heat exchange approaches 99% efficiency.<ref>{{cite journal |last1=Cech |first1=Joseph J. |last2=Laurs |first2=R. Michael |last3=Graham |first3=Jeffrey B. | title = Temperature-Induced Changes in Blood Gas Equilibria in the Albacore, ''Thunnus alalunga'', a Warm-Bodied Tuna |journal=[[Journal of Experimental Biology]] | volume = 109 | issue = 1 | pages = 21–34 | date = March 1, 1984 |doi=10.1242/jeb.109.1.21 | url = http://jeb.biologists.org/content/109/1/21.abstract |doi-access=free }}</ref><ref name="Taylor1982">{{cite book|last=Taylor|first=Richard C.|title=A Companion to Animal Physiology|url={{google books|id=_aQ5AAAAIAAJ|page=228|plainurl=yes}}|date=30 April 1982|publisher=CUP Archive|isbn=978-0-521-24437-4|page=228}}</ref>

== Birds ==
In [[bird]]s with [[Webbed foot|webbed feet]], retia mirabilia in the legs and feet transfer heat from the outgoing (hot) blood in the arteries to the incoming (cold) blood in the veins. The effect of this biological [[heat exchanger]] is that the internal temperature of the feet is much closer to the ambient temperature, thus reducing heat loss. [[Penguin]]s also have them in the flippers and nasal passages.

Seabirds distill seawater using [[countercurrent exchange]] in a so-called [[salt gland]] with a rete mirabile. The gland secretes highly concentrated brine stored near the nostrils above the beak. The bird then "sneezes" the brine out. As freshwater is not usually available in their environments, some seabirds, such as [[pelican]]s, [[petrel]]s, [[albatross]]es, [[gull]]s and [[tern]]s, possess this gland, which allows them to drink the salty water from their environments while they are hundreds of miles away from land.<ref>{{cite book|last1=Proctor|first1=Noble S.|last2=Lynch|first2=Patrick J.|title=Manual of Ornithology|isbn=0300076193|year=1993|publisher=Yale University Press}}</ref><ref>{{cite web|last=Ritchison|first=Gary|title=Avian osmoregulation » Urinary System, Salt Glands, and Osmoregulation |url=http://people.eku.edu/ritchisong/bird_excretion.htm|access-date=16 April 2011}} including images of the gland and its function</ref>

== Fish ==
Fish have evolved retia mirabilia multiple times to raise the temperature<ref name=Runcie2009>{{Cite journal| doi = 10.1242/jeb.022814| issn = 0022-0949 | eissn=1477-9145| volume = 212| issue = 4| pages = 461–470| last1 = Runcie| first1 = Rosa M.| last2 = Dewar| first2 = Heidi| last3 = Hawn| first3 = Donald R.| last4 = Frank| first4 = Lawrence R.| last5 = Dickson| first5 = Kathryn A.| title = Evidence for cranial endothermy in the opah (Lampris guttatus)| journal = Journal of Experimental Biology| date = 2009-02-15| pmid = 19181893| pmc = 2726851 | doi-access = free}}</ref> ([[endotherm]]y) or the oxygen concentration of a body part above the ambient level.<ref name=Berenbrink2007>{{Cite journal| doi = 10.1242/jeb.003319| issn = 0022-0949| eissn= 1477-9145| volume = 210| issue = 9| pages = 1641–1652| last = Berenbrink| first = Michael| title = Historical reconstructions of evolving physiological complexity: O<sub>2</sub> secretion in the eye and swimbladder of fishes| journal = Journal of Experimental Biology| accessdate = 2021-02-18| date = 2007-05-01| url = https://jeb.biologists.org/content/210/9/1641| pmid = 17449830| doi-access = | url-access = subscription}}</ref>

In many [[fish]], a rete mirabile helps fill the [[swim bladder]] with [[oxygen]], increasing the fish's [[buoyancy]]. The rete mirabile is an essential<ref name=Berenbrink2007/> part of the system that pumps dissolved oxygen from a low [[partial pressure]] (<math>{P_{\rm O_2}}</math>) of 0.2 [[Atmospheric pressure|atmospheres]] into a gas filled bladder that is at a pressure of hundreds of atmospheres.<ref name=Pelster2001>{{Cite journal| doi = 10.1152/physiologyonline.2001.16.6.287| issn = 1548-9213| volume = 16| issue = 6| pages = 287–291| last = Pelster| first = Bernd| title = The Generation of Hyperbaric Oxygen Tensions in Fish| journal = Physiology| accessdate = 2021-02-18| date = 2001-12-01| pmid = 11719607| url = https://journals.physiology.org/doi/full/10.1152/physiologyonline.2001.16.6.287| url-access = subscription}}</ref> A rete mirabile called the '''choroid rete mirabile''' is found in most living [[teleost]]s and raises the <math>{P_{\rm O_2}}</math> of the retina.<ref name=Berenbrink2007/> The higher supply of oxygen allows the teleost retina to be thick and have few blood vessels thereby [[Retina#Inverted versus non-inverted retina|increasing its sensitivity to light]].<ref name="Damsgaard2021">{{Cite journal| doi = 10.1016/j.cbpa.2020.110840| issn = 1095-6433| volume = 252| pages = 110840| last = Damsgaard| first = Christian| title = Physiology and evolution of oxygen secreting mechanism in the fisheye| journal = Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology| date = 2021-02-01| pmid = 33166685| doi-access = }}</ref> In addition to raising the <math>{P_{\rm O_2}}</math>, the choroid rete has evolved to raise the temperature of the eye in some teleosts and [[sharks]].<ref name=Runcie2009/>

A [[countercurrent exchange system]] is utilized between the venous and arterial capillaries.  Lowering the [[pH]] levels in the venous capillaries causes oxygen to unbind from blood [[hemoglobin]] because of the [[Root effect]]. This causes an increase in venous blood oxygen partial pressure, allowing the oxygen to diffuse through the capillary membrane and into the arterial capillaries, where oxygen is still sequestered to hemoglobin. The cycle of diffusion continues until the partial pressure of oxygen in the arterial capillaries exceeds that in the swim bladder. At this point, the dissolved oxygen in the arterial capillaries diffuses into the swim bladder via the gas gland.<ref>{{cite book | last = Kardong | first = K. | date = 2008 | title = Vertebrates: Comparative anatomy, function, evolution | edition = 5th  | location = Boston | publisher = McGraw-Hill }}</ref>

The rete mirabile allows for an increase in muscle temperature in regions where this network of vein and arteries is found.  The fish is able to [[thermoregulate]] certain areas of its body.  Additionally, this increase in temperature leads to an increase in basal metabolic temperature.  The fish is now able to split [[Adenosine triphosphate|ATP]] at a higher rate and ultimately can swim faster.

The [[opah]] utilizes retia mirabilia to conserve heat, making it the newest addition to the list of regionally endothermic fish. Blood traveling through capillaries in the gills must carry cold blood due to their exposure to cold water, but retia mirabilia in the opah's [[gills]] are able to transfer heat from warm blood in arterioles coming from the heart that heats this colder blood in arterioles leaving the gills. The huge [[pectoral fin|pectoral muscles]] of the opah, which generate most of the body heat, are thus able to control the temperature of the rest of the body.<ref name="Ed Yong 2015">{{cite journal | title = Whole-body endothermy in a mesopelagic fish, the opah, Lampris guttatus | first1 = Nicholas C. | last1 = Wegner | first2 = Owyn E. | last2 = Snodgrass | first3 = Heidi | last3 = Dewar | first4 = John R. | last4 = Hyde | journal = [[Science (journal)|Science]] | doi = 10.1126/science.aaa8902 | date = 15 May 2015 | volume = 348 | issue = 6236 | pages = 786–789 | pmid=25977549| bibcode = 2015Sci...348..786W | s2cid = 17412022 }}</ref>

==Mammals==
{{more references|section|date=February 2021}}
In [[mammal]]s, an elegant rete mirabile in the [[efferent arteriole]]s of [[juxtamedullary glomeruli]] is important in maintaining the [[Tonicity#Hypertonic solution|hypertonicity]] of the [[renal medulla]]. It is the hypertonicity of this zone, resorbing water [[osmosis|osmotically]] from the renal collecting ducts as they exit the [[kidney]], that makes possible the excretion of a hypertonic [[urine]] and maximum conservation of body water.

Vascular retia mirabilia are also found in the limbs of a range of mammals. These reduce the temperature in the extremities. Some of these probably function to prevent heat loss in cold conditions by reducing the temperature gradient between the limb and the environment. Others reduce the temperature of the [[testes]] increasing their productivity. In the neck of the [[dog]], a rete mirabile protects the brain when the body overheats during hunting; the venous blood is cooled down by panting before entering the net.

Retia mirabilia also occur frequently in mammals that burrow, dive or have arboreal lifestyles that involve clinging with the limbs for lengthy periods.   In the last case, slow-moving arboreal mammals such as sloths, lorises and arboreal anteaters possess retia of the highly developed type known as vascular bundles. The structure and function of these mammalian retia mirabilia are reviewed by O'Dea (1990).<ref>{{cite journal | last = O'Dea | first = J. D | date = 1990 | title = The mammalian ''Rete mirabile'' and oxygen availability | journal = Comparative Biochemistry and Physiology A | volume = 95A | issue = 1 | pages = 23–25 | doi = 10.1016/0300-9629(90)90004-C }}</ref>

The ancient physician [[Galen]] mistakenly thought that [[human]]s also have a rete mirabile in the neck, apparently based on dissection of [[sheep]] and misidentifying the results with the human [[carotid sinus]], and ascribed important properties to it; it fell to [[Berengario da Carpi]] first, and then to [[Vesalius]] to demonstrate the error.

== See also ==
* [[Pampiniform venous plexus|Pampiniform plexus]], a countercurrent heat-exchanging structure in the spermatic cord

== References ==
{{Reflist}}

== External links ==
* [http://www.lookd.com/fish/gasbladder.html Fish gas bladder with an adjacent rete mirabile]

{{Arteries and veins}}
{{Authority control}}

{{DEFAULTSORT:Rete Mirabile}}
[[Category:Cardiovascular system anatomy]]
[[Category:Circulatory system]]
[[Category:Vertebrate anatomy]]
[[Category:Latin biological phrases]]