Warm-blooded

<h2 id="terminology">Terminology</h2>
In general, warm-bloodedness refers to three separate categories of <a href="/facts/Thermoregulation/V692hIjw">thermoregulation</a>.

<ul><li><a href="/facts/Endotherm/qs3DIGHx">Endothermy</a><a class="footnote-ref" id="fnref:1" href="#fn:1">1</a> is the ability of some creatures to control their body temperatures through internal means such as muscle shivering or increasing their <a href="/facts/Metabolism/WxDrm8k5">metabolism</a>. The opposite of endothermy is <a href="/facts/Ectothermy/vdjXLuQr">ectothermy</a>.</li>
<li><a href="/facts/Homeotherm/vf5or2Cj">Homeothermy</a><a class="footnote-ref" id="fnref:2" href="#fn:2">2</a> maintains a stable internal body temperature regardless of external influence and temperatures. The stable internal temperature is often higher than the immediate environment. The opposite is <a href="/facts/Poikilothermy/mqqYSlcq">poikilothermy</a>. The only known living homeotherms are <a href="/facts/Mammal/phSwTzBo">mammals</a> and <a href="/facts/Bird/RJF6zwLP">birds</a>, as well as one lizard, the <a href="/facts/Argentine_black_and_white_tegu/tjn2b7sK">Argentine black and white tegu</a>. Some extinct reptiles such as <a href="/facts/Ichthyosaur/fBNIIJaJ">ichthyosaurs</a>, <a href="/facts/Pterosaur/YNQwa1ru">pterosaurs</a>, <a href="/facts/Plesiosaur/Tbfbj8kH">plesiosaurs</a> and some non-avian <a href="/facts/Dinosaur/JRdMqBnq">dinosaurs</a> are believed to have been homeotherms.</li>
<li>Tachymetabolism<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a> maintains a high "resting" metabolism. In essence, tachymetabolic creatures are "on" all the time. Though their resting metabolism is still many times slower than their active metabolism, the difference is often not as large as that seen in <a href="/facts/Bradymetabolic/uaBfm7aj">bradymetabolic</a> creatures. Tachymetabolic creatures have greater difficulty dealing with a scarcity of food.</li></ul>
<h2 id="varieties-of-thermoregulation">Varieties of thermoregulation</h2>
A significant proportion of creatures commonly referred to as "warm-blooded," like birds and mammals, exhibit all three of these categories (i.e., they are endothermic, homeothermic, and tachymetabolic). However, over the past three decades, investigations in the field of animal thermophysiology have unveiled numerous species within these two groups that do not meet all these criteria. For instance, many bats and small birds become poikilothermic and bradymetabolic during sleep (or, in nocturnal species, during the day). For such creatures, the term <a href="/facts/Heterothermy/5FHnMHnM">heterothermy</a> was introduced.
Further examinations of animals traditionally classified as <a href="/facts/Ectotherm/vdjXLuQr">cold-blooded</a> have revealed that most creatures manifest varying combinations of the three aforementioned terms, along with their counterparts (ectothermy, poikilothermy, and bradymetabolism), thus creating a broad spectrum of body temperature types. Some <a href="/facts/Fish/fln4gH9V">fish</a> have warm-blooded characteristics, such as the <a href="/facts/Opah/PfASNrrp">opah</a>. <a href="/facts/Swordfish/yjNzRNBE">Swordfish</a> and some <a href="/facts/Shark/rh5Cotvx">sharks</a> have <a href="/facts/Circulatory_system/WXwudzzc">circulatory</a> mechanisms that keep their <a href="/facts/Brain/EKla9NkJ">brains</a> and <a href="/facts/Eye/h3lbYU55">eyes</a> above ambient temperatures and thus increase their ability to detect and react to <a href="/facts/Predation/JEGdrX3f">prey</a>.<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a><a class="footnote-ref" id="fnref:5" href="#fn:5">5</a><a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> Tunas and some sharks have similar mechanisms in their muscles, improving their stamina when swimming at high speed.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>

<h2 id="heat-generation">Heat generation</h2>
Main article: <a href="/facts/Thermogenesis/aA6HD0At">Thermogenesis</a>
Body heat is <a href="/facts/Thermogenesis/aA6HD0At">generated</a> by <a href="/facts/Metabolism/WxDrm8k5">metabolism</a>.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> This relates to the chemical reaction in <a href="/facts/Cell_(biology)/bLM9UQvy">cells</a> that break down <a href="/facts/Glucose/oUSkoLCD">glucose</a> into water and <a href="/facts/Carbon_dioxide/xGzpppEp">carbon dioxide</a>, thereby producing <a href="/facts/Adenosine_triphosphate/nB9bwgcU">adenosine triphosphate</a> (ATP), a high-energy compound used to power other cellular processes. Muscle contraction is one such metabolic process generating heat energy,<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> and additional heat results from friction as blood circulates through the vascular system in premise to their specialized fat <a href="/facts/Cell_(biology)/bLM9UQvy">cells</a> which produce heat through uncoupled <a href="/facts/Respiration_(physiology)/KKWAJIbd">respiration</a>, contributing to <a href="/facts/Thermoregulation/V692hIjw">thermoregulation</a>.
All organisms metabolize food and other inputs, but some make better use of the output than others. Like all energy conversions, metabolism is rather inefficient, and around 60% of the available energy is converted to heat rather than to ATP.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> In most organisms, this heat dissipates into the surroundings. However, endothermic homeotherms (generally referred to as "warm-blooded" animals) not only produce more heat but also possess superior means of retaining and regulating it compared to other animals. They exhibit a higher basal metabolic rate and can further increase their metabolic rate during strenuous activity. They usually have well-developed insulation in order to retain body heat: fur and <a href="/facts/Blubber/NEyrDtbM">blubber</a> in the case of mammals and <a href="/facts/Feather/sxbf96nF">feathers</a> in birds. When this insulation is insufficient to maintain body temperature, they may resort to <a href="/facts/Shivering/Tl80pLQH">shivering</a>—rapid muscle contractions that quickly use up ATP, thus stimulating cellular metabolism to replace it and consequently produce more heat. Additionally, almost all <a href="/facts/Eutheria/3fPKIKxx">eutherian</a> mammals (with the only known exception being <a href="/facts/Swine/r8rtDBIH">swine</a>) have <a href="/facts/Brown_adipose_tissue/ut8P9TLS">brown adipose tissue</a> whose <a href="/facts/Mitochondrion/ErHqrdJ1">mitochondria</a> are capable of <a href="/facts/Non-shivering_thermogenesis/aA6HD0At">non-shivering thermogenesis</a>.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> This process involves the direct dissipation of the mitochondrial gradient as heat via an <a href="/facts/Uncoupling_protein/xWzlSmVm">uncoupling protein</a>, thereby "uncoupling" the gradient from its usual function of driving ATP production via <a href="/facts/ATP_synthase/5NBMxsVX">ATP synthase</a>.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>
In warm environments, these animals employ evaporative cooling to shed excess heat, either through <a href="/facts/Sweating/c5zARtaT">sweating</a> (some mammals) or by <a href="/facts/Thermoregulation/V692hIjw">panting</a> (many mammals and all birds)—mechanisms generally absent in poikilotherms.

<h2 id="defense-against-fungi">Defense against fungi</h2>
It has been hypothesized that warm-bloodedness evolved in mammals and birds as a defense against <a href="/facts/Fungal_infection/YVK551qC">fungal infections</a>. Very few fungi can survive the body temperatures of warm-blooded animals. By comparison, insects, reptiles, and amphibians are plagued by fungal infections.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a><a class="footnote-ref" id="fnref:14" href="#fn:14">14</a><a class="footnote-ref" id="fnref:15" href="#fn:15">15</a><a class="footnote-ref" id="fnref:16" href="#fn:16">16</a> Warm-blooded animals have a defense against pathogens contracted from the environment, since environmental pathogens are not adapted to their higher internal temperature.<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Argentine_black_and_white_tegu/tjn2b7sK">Argentine black and white tegu § Endothermic behavior</a></li>
<li><a href="/facts/Mesotherm/J9S5TE7I">Mesotherm</a></li>
<li><a href="/facts/Thermogenic_plant/KXVI2484">Thermogenic plant</a></li></ul>

Footnotes

Citations

<h2 id="external-links">External links</h2>

Look up warm-blooded in Wiktionary, the free dictionary.

<ul><li><a href="https://www.earthlife.net/mammals/warm.html">What is Warm Blooded??</a></li>
<li><a href="http://reptilis.net/cold-blood.html">The Reptipage: What is cold-blooded?</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Greek: ἔνδον endon "within" θέρμη thermē "heat" <a href="/wiki/Ancient_Greek" target="_blank">/wiki/Ancient_Greek</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Greek: ὅμοιος homoios "similar", θέρμη thermē "heat" <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Greek: ταχύς tachys or tachus "fast, swift", μεταβάλλειν metaballein "turn quickly" <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Hot Eyes for Cold Fish – Wong 2005 (110): 2 – ScienceNOW <a href="http://sciencenow.sciencemag.org/cgi/content/full/2005/110/2" target="_blank">http://sciencenow.sciencemag.org/cgi/content/full/2005/110/2</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">Block, B.A. & Carey, F.G. (March 1985). "Warm brain and eye temperatures in sharks". Journal of Comparative Physiology B. 156 (2): 229–36. doi:10.1007/BF00695777. PMID 3836233. S2CID 33962038. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">"Warm eyes give deep-sea predators super vision". University of Queensland. 11 January 2005. <a href="http://www.uq.edu.au/news/?article=6503" target="_blank">http://www.uq.edu.au/news/?article=6503</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">McFarlane, P. (January 1999). "Warm-Blooded Fish". Monthly Bulletin of the Hamilton and District Aquarium Society. Archived from the original on 15 May 2013. Retrieved 31 May 2008. <a href="https://web.archive.org/web/20130515103309/http://www.aquarticles.com/articles/breeding/McFarlane_Warm_Blooded_Fish.html" target="_blank">https://web.archive.org/web/20130515103309/http://www.aquarticles.com/articles/breeding/McFarlane_Warm_Blooded_Fish.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Yousef, Hani; Ramezanpour Ahangar, Edris; Varacallo, Matthew (2024), "Physiology, Thermal Regulation", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 29763018, retrieved 28 February 2024 <a href="http://www.ncbi.nlm.nih.gov/books/NBK499843/" target="_blank">http://www.ncbi.nlm.nih.gov/books/NBK499843/</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Periasamy, Muthu; Herrera, Jose Luis; Reis, Felipe C. G. (24 October 2017). "Skeletal Muscle Thermogenesis and Its Role in Whole Body Energy Metabolism". Diabetes & Metabolism Journal. 41 (5): 327–336. doi:10.4093/dmj.2017.41.5.327. PMC 5663671. PMID 29086530. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5663671" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5663671</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Macherel, David; Haraux, Francis; Guillou, Hervé; Bourgeois, Olivier (1 February 2021). "The conundrum of hot mitochondria" (PDF). Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1862 (2): 148348. doi:10.1016/j.bbabio.2020.148348. ISSN 0005-2728. PMID 33248118. <a href="https://hal.science/hal-03102332/file/Version%20HAL%20BBABIOv2.pdf" target="_blank">https://hal.science/hal-03102332/file/Version%20HAL%20BBABIOv2.pdf</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Berg, Frida; Gustafson, Ulla; Andersson, Leif (18 August 2006). "The Uncoupling Protein 1 Gene (UCP1) Is Disrupted in the Pig Lineage: A Genetic Explanation for Poor Thermoregulation in Piglets". PLOS Genetics. 2 (8): e129. doi:10.1371/journal.pgen.0020129. ISSN 1553-7404. PMC 1550502. PMID 16933999. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1550502" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1550502</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Cannon, Barbara; Nedergaard, Jan (1 January 2004). "Brown Adipose Tissue: Function and Physiological Significance". Physiological Reviews. 84 (1): 277–359. doi:10.1152/physrev.00015.2003. ISSN 0031-9333. PMID 14715917. <a href="https://www.physiology.org/doi/10.1152/physrev.00015.2003" target="_blank">https://www.physiology.org/doi/10.1152/physrev.00015.2003</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Dunn, Rob (2011). "Killer Fungi Made us Hotblooded". New Scientist. Retrieved 27 April 2016.(subscription required) <a href="https://www.newscientist.com/article/mg21228411.700-killer-fungi-made-us-hotblooded.html#.UeTeVY0wd8E" target="_blank">https://www.newscientist.com/article/mg21228411.700-killer-fungi-made-us-hotblooded.html#.UeTeVY0wd8E</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Aviv Bergman, Arturo Casadevall. 2010. Mammalian Endothermy Optimally Restricts Fungi and Metabolic Costs. mBio Nov 2010, 1 (5) e00212-10. doi:10.1128/mBio.00212-10 <a href="https://mbio.asm.org/content/1/5/e00212-10.full?sid=eb1e9d14-ab01-4d2f-9e5b-623a13ae278f" target="_blank">https://mbio.asm.org/content/1/5/e00212-10.full?sid=eb1e9d14-ab01-4d2f-9e5b-623a13ae278f</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">Vincent A. Robert, Arturo Casadevall. 2009. Vertebrate Endothermy Restricts Most Fungi as Potential Pathogens. The Journal of Infectious Diseases, Volume 200, Issue 10, 15 November 2009, Pages 1623–1626. doi:10.1086/644642 <a href="https://academic.oup.com/jid/article/200/10/1623/881601" target="_blank">https://academic.oup.com/jid/article/200/10/1623/881601</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">Casadevall A (2012) Fungi and the Rise of Mammals. PLoS Pathog 8(8): e1002808. doi:10.1371/journal.ppat.1002808 <a href="https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1002808" target="_blank">https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1002808</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">Robert, Vincent A.; Casadevall, Arturo (15 November 2009). "Vertebrate Endothermy Restricts Most Fungi as Potential Pathogens". The Journal of Infectious Diseases. 200 (10): 1623–1626. doi:10.1086/644642. ISSN 0022-1899. PMID 19827944. <a href="https://doi.org/10.1086%2F644642" target="_blank">https://doi.org/10.1086%2F644642</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
</ol>

Warm-blooded open-in-new

Warm-blooded