Editing Rete mirabile (section)

== 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>