Editing Thermoregulation (section)

==Vertebrates==
By numerous observations upon [[homo sapiens sapiens|humans]] and other animals, [[John Hunter (surgeon)|John Hunter]] showed that the essential difference between the so-called [[warm-blooded]] and [[Poikilotherm|cold-blooded]] animals lies in observed constancy of the temperature of the former, and the observed variability of the temperature of the latter. Almost all birds and mammals have a high temperature almost constant and independent of that of the surrounding air ([[Homeothermic|homeothermy]]). Almost all other animals display a variation of body temperature, dependent on their surroundings ([[Poikilothermic|poikilothermy]]).{{sfn|Chisholm|1911|p=49}}

===Brain control===
Thermoregulation in both ectotherms and endotherms is primarily controlled by the [[preoptic area]] (POA) of the [[anterior hypothalamus]].<ref>{{Cite journal |last=Nakamura |first=Kazuhiro |date=November 2011 |title=Central circuitries for body temperature regulation and fever |url=https://www.physiology.org/doi/10.1152/ajpregu.00109.2011 |journal=American Journal of Physiology-Regulatory, Integrative and Comparative Physiology |language=en |volume=301 |issue=5 |pages=R1207–R1228 |doi=10.1152/ajpregu.00109.2011 |issn=0363-6119}}</ref><ref name="Romanovsky">{{cite journal |last1=Romanovsky |first1=AA |year=2007 |title=Functional architecture of the thermoregulatory system |url=https://semanticscholar.org/paper/dbed9c21ecd8a7a55872711ba65f45814b0f5f6e |journal=Am J Physiol Regul Integr Comp Physiol |volume=292 |issue=1 |pages=R37–46 |doi=10.1152/ajpregu.00668.2006 |pmid=17008453 |s2cid=1163257}}</ref><ref>{{Cite journal |last=Morrison |first=S.F. |last2=Nakamura |first2=K. |date=2019-02-10 |title=Central Mechanisms for Thermoregulation |url=https://www.annualreviews.org/doi/10.1146/annurev-physiol-020518-114546 |journal=Annual Review of Physiology |language=en |volume=81 |issue=1 |pages=285–308 |doi=10.1146/annurev-physiol-020518-114546 |issn=0066-4278}}</ref> In rats, neurons in the POA that express the [[prostaglandin E receptor 3]] (EP3) play a crucial role in thermoregulation by regulating body temperature in both directions.<ref name=":2">{{Cite journal |last=Nakamura |first=Yoshiko |last2=Yahiro |first2=Takaki |last3=Fukushima |first3=Akihiro |last4=Kataoka |first4=Naoya |last5=Hioki |first5=Hiroyuki |last6=Nakamura |first6=Kazuhiro |date=2022-12-23 |title=Prostaglandin EP3 receptor–expressing preoptic neurons bidirectionally control body temperature via tonic GABAergic signaling |url=https://www.science.org/doi/10.1126/sciadv.add5463 |journal=Science Advances |language=en |volume=8 |issue=51 |doi=10.1126/sciadv.add5463 |issn=2375-2548 |pmc=9788766 |pmid=36563142}}</ref> EP3-expressing neurons in the POA provide continuous (tonic) inhibitory signals with the transmitter [[GABA|gamma-aminobutyric acid (GABA)]] to control [[Sympathetic nervous system|sympathetic]] output neurons in the [[dorsomedial hypothalamus]] (DMH) and the rostral [[raphe]] pallidus nucleus of the [[medulla oblongata]] (rRPa).<ref name=":2" /><ref name=":3">{{Cite journal |last=Nakamura |first=Kazuhiro |last2=Matsumura |first2=Kiyoshi |last3=Kaneko |first3=Takeshi |last4=Kobayashi |first4=Shigeo |last5=Katoh |first5=Hironori |last6=Negishi |first6=Manabu |date=2002-06-01 |title=The Rostral Raphe Pallidus Nucleus Mediates Pyrogenic Transmission from the Preoptic Area |url=https://www.jneurosci.org/lookup/doi/10.1523/JNEUROSCI.22-11-04600.2002 |journal=The Journal of Neuroscience |language=en |volume=22 |issue=11 |pages=4600–4610 |doi=10.1523/JNEUROSCI.22-11-04600.2002 |issn=0270-6474 |pmc=6758794 |pmid=12040067}}</ref> In a hot environment, the tonic inhibitory signals from EP3-expressing POA neurons are augmented to suppress sympathetic output. This results in suppressed heat production and dilated skin blood vessels, the latter of which promote heat loss from the body surface. In a cold environment, the tonic inhibition from EP3-expressing POA neurons is attenuated to increase (disinhibit) sympathetic output. This results in increased heat production and constricted skin blood vessels to reduce heat loss.<ref name=":2" /><ref>{{Cite journal |last=Nakamura |first=Kazuhiro |last2=Nakamura |first2=Yoshiko |last3=Kataoka |first3=Naoya |date=January 2022 |title=A hypothalamomedullary network for physiological responses to environmental stresses |url=https://www.nature.com/articles/s41583-021-00532-x |journal=Nature Reviews Neuroscience |language=en |volume=23 |issue=1 |pages=35–52 |doi=10.1038/s41583-021-00532-x |issn=1471-003X}}</ref> The tonic inhibition from EP3-expressing POA neurons is also attenuated by an action of [[Prostaglandin E2|prostaglandin E<sub>2</sub>]] (PGE<sub>2</sub>) to induce [[fever]].<ref name=":2" /> This tonic inhibitory control of body temperature was first proposed as a fever mechanism in 2002<ref name=":3" /> and was demonstrated to be the fundamental principle of body temperature [[homeostasis]] in mammals in 2022.<ref name=":2" /> Such homeostatic control is separate from the [[Sense#Temperature|sensation of temperature]].<ref>{{Cite journal |last=Nakamura |first=Kazuhiro |last2=Morrison |first2=Shaun F |date=January 2008 |title=A thermosensory pathway that controls body temperature |url=https://www.nature.com/articles/nn2027 |journal=Nature Neuroscience |language=en |volume=11 |issue=1 |pages=62–71 |doi=10.1038/nn2027 |issn=1097-6256 |pmc=2423341 |pmid=18084288}}</ref><ref>{{Cite journal |last=Yahiro |first=Takaki |last2=Kataoka |first2=Naoya |last3=Nakamura |first3=Yoshiko |last4=Nakamura |first4=Kazuhiro |date=2017-07-10 |title=The lateral parabrachial nucleus, but not the thalamus, mediates thermosensory pathways for behavioural thermoregulation |url=https://www.nature.com/articles/s41598-017-05327-8 |journal=Scientific Reports |language=en |volume=7 |issue=1 |doi=10.1038/s41598-017-05327-8 |issn=2045-2322 |pmc=5503995 |pmid=28694517}}</ref>

===In birds and mammals===
[[File:Kangaroo licking itself to cool.jpg|thumb|upright|Kangaroo [[licking]] its arms to cool down]]
In cold environments, birds and mammals employ the following adaptations and strategies to minimize heat loss:{{cn|date=March 2025}}
# Using small smooth muscles ([[arrector pili]] in mammals), which are attached to feather or hair shafts; this distorts the surface of the skin making feather/hair shaft stand erect (called [[goose bumps]] or goose pimples) which slows the movement of air across the skin and minimizes heat loss.
# Increasing body size to more easily maintain core body temperature (warm-blooded animals in cold climates tend to be larger than similar species in warmer climates (see [[Bergmann's rule]]))
# Having the ability to store energy as fat for [[metabolism]]
# Have shortened extremities
# Have [[countercurrent exchange|countercurrent blood flow]] in extremities – this is where the warm arterial blood travelling to the limb passes the cooler venous blood from the limb and heat is exchanged warming the venous blood and cooling the arterial (e.g., [[Arctic wolf]]<ref>{{Cite journal | last = Swan | first = K. G. |author2=R. E. Henshaw | title = Lumbar sympathectomy and cold acclimatization by the arctic wolf | journal = Annals of Surgery| volume = 177 | issue =3 | pages = 286–292 |date=March 1973 | doi=10.1097/00000658-197303000-00008 | pmid = 4692116 | pmc = 1355529}}</ref> or penguins<ref>[http://www.seaworld.org/infobooks/Penguins/adaptations.html Adaptations for an Aquatic Environment] {{Webarchive|url=https://web.archive.org/web/20090302074545/http://seaworld.org/infobooks/penguins/adaptations.html |date=2 March 2009 }}. SeaWorld/Busch Gardens Animal Information Database, 2002. Last accessed 27 November 2006.</ref>)
In warm environments, birds and mammals employ the following adaptations and strategies to maximize heat loss:
# Behavioural adaptations like living in burrows during the day and being nocturnal
# Evaporative cooling by perspiration and panting
# Storing fat reserves in one place (e.g., camel's hump) to avoid its insulating effect
# Elongated, often vascularized extremities to conduct body heat to the air

In humans
{{main|Thermoregulation in humans}}

[[File:Thermoregulation simplified.png|thumb|upright=1.9|Simplified [[Control theory|control circuit]] of human thermoregulation.<ref>{{cite journal | last1 = Kanosue | first1 = K. | last2 = Crawshaw | first2 = L. I. | last3 = Nagashima | first3 = K. | last4 = Yoda | first4 = T. | year = 2009 | title = Concepts to utilize in describing thermoregulation and neurophysiological evidence for how the system works | journal = European Journal of Applied Physiology | volume = 109 | issue = 1| pages = 5–11 | doi = 10.1007/s00421-009-1256-6 | pmid = 19882166 | s2cid = 11103870 }}</ref>]]
As in other mammals, thermoregulation is an important aspect of human [[homeostasis]]. Most body heat is generated in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles.<ref name="GuytonHall2006p80">{{cite book |year=2006 |author=Guyton, A.C. |author2=Hall, J.E. |title=Textbook of Medical Physiology |edition=11th |place=Philadelphia |publisher=Elsevier Saunders |page=890}}</ref> Humans have been able to adapt to a great diversity of climates, including hot humid and hot arid. High temperatures pose serious stresses for the human body, placing it in great danger of injury or even death. For example, one of the most common reactions to hot temperatures is heat exhaustion, which is an illness that could happen if one is exposed to high temperatures, resulting in some symptoms such as dizziness, fainting, or a rapid heartbeat.<ref>"Heat Exhaustion: Symptoms and Treatment". WebMD. Retrieved 2017-03-01</ref><ref>Harmon, Katherine. "How Does a Heat Wave Affect the Human Body?". Scientific American. Retrieved 2017-03-01</ref> For humans, [[adaptation]] to varying climatic conditions includes both physiological mechanisms resulting from [[evolution]] and behavioural mechanisms resulting from conscious cultural adaptations.<ref name=" humanbiology3rded">Harrison, G.A., Tanner, J.M., Pilbeam, D.R., & Baker, P.T. (1988) ''Human Biology: An introduction to human evolution, variation, growth, and adaptability''. (3rd ed). Oxford: Oxford University Press</ref><ref name=" Humanbiology&behaviour4thed">Weiss, M.L., & Mann, A.E. (1985) ''Human Biology and Behaviour: An anthropological perspective''. (4th ed). Boston: Little Brown</ref> The physiological control of the body's core temperature takes place primarily through the hypothalamus, which assumes the role as the body's "thermostat".<ref>"Thermoregulation". www.unm.edu. Retrieved 2017-03-01.</ref> This organ possesses control mechanisms as well as key temperature sensors, which are connected to nerve cells called thermoreceptors.<ref>Boundless (26 May 2016). "Thermoreception". Boundless.</ref> Thermoreceptors come in two subcategories; ones that respond to cold temperatures and ones that respond to warm temperatures. Scattered throughout the body in both peripheral and central nervous systems, these nerve cells are sensitive to changes in temperature and are able to provide useful information to the hypothalamus through the process of negative feedback, thus maintaining a constant core temperature.<ref>{{cite journal | last1 = Tansey | first1 = Etain A. | last2 = Johnson | first2 = Christopher D. | year = 2015 | title = Recent advances in thermoregulation | url = https://pure.qub.ac.uk/ws/files/119849020/Recent_advances_in_thermoregulation.pdf| journal = Advances in Physiology Education | volume = 39 | issue = 3| pages = 139–148 | doi = 10.1152/advan.00126.2014 | pmid = 26330029 | s2cid = 11553866 }}</ref><ref>"Temperature Regulation of the Human Body". hyperphysics.phy-astr.gsu.edu. Retrieved 2017-03-01.</ref>
[[File:Irish Wolfhound mix, panting.ogv|thumb|A dog panting after exercise]]

There are four avenues of heat loss: evaporation, convection, conduction, and radiation. If skin temperature is greater than that of the surrounding air temperature, the body can lose heat by convection and conduction. However, if air temperature of the surroundings is greater than that of the skin, the body ''gains'' heat by convection and conduction. In such conditions, the only means by which the body can rid itself of heat is by evaporation. So, when the surrounding temperature is higher than the skin temperature, anything that prevents adequate evaporation will cause the internal body temperature to rise.<ref name=GuytonHall2006pp891892>Guyton & Hall (2006), pp. 891–892</ref> During intense physical activity (e.g. sports), evaporation becomes the main avenue of heat loss.<ref>Wilmore, Jack H., & Costill, David L. (1999). ''Physiology of sport and exercise'' (2nd ed). Champaign, Illinois: Human Kinetics.</ref> Humidity affects thermoregulation by limiting sweat evaporation and thus heat loss.<ref name=" textbookofmedicalphysiology5thed">Guyton, Arthur C. (1976) ''Textbook of Medical Physiology''. (5th ed). Philadelphia: W.B. Saunders</ref>

=== In reptiles ===
Thermoregulation is also an integral part of a reptile's life, specifically lizards such as ''[[Microlophus occipitalis]]'' and ''[[Ctenophorus decresii]]'' who must change microhabitats to keep a constant body temperature.<ref>{{Cite journal|last1=Jordán A.|first1=Juan C.|last2=Pérez Z.|first2=José|date=2013-06-25|title=Thermal ecology of Microlophus occipitalis (Sauria: Tropiduridae) in the Plain Dry Forest of Tumbes, Peru.|journal=Revista Peruana de Biología|url=http://ateneo.unmsm.edu.pe//handle/123456789/2239|language=en|issn=1561-0837|access-date=9 December 2021|archive-date=19 May 2022|archive-url=https://web.archive.org/web/20220519060852/http://ateneo.unmsm.edu.pe/handle/123456789/2239|url-status=dead}}</ref><ref>{{Cite journal|last1=Walker|first1=Samantha|last2=Stuart-Fox|first2=Devi|last3=Kearney|first3=Michael R.|date=December 2015|title=Has contemporary climate change played a role in population declines of the lizard Ctenophorus decresii from semi-arid Australia?|url=https://linkinghub.elsevier.com/retrieve/pii/S0306456514001764|journal=Journal of Thermal Biology|language=en|volume=54|pages=66–77|doi=10.1016/j.jtherbio.2014.12.001|pmid=26615728|bibcode=2015JTBio..54...66W }}</ref> By moving to cooler areas when it is too hot and to warmer areas when it is cold, they can thermoregulate their temperature to stay within their necessary bounds.{{cn|date=March 2024}}