Warm-blooded
| Thermoregulation in animals |
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Warm-blooded is an informal term referring to
As there are more than two categories of temperature control utilized by animals, the terms warm-blooded and cold-blooded have been deprecated in the scientific field.
Terminology
In general, warm-bloodedness refers to three separate categories of thermoregulation.
- ectothermy.
- are believed to have been homeotherms.
- Tachymetabolismbradymetabolic creatures. Tachymetabolic creatures have greater difficulty dealing with a scarcity of food.[citation needed]
Varieties of thermoregulation
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 heterothermy was introduced.
Further examinations of animals traditionally classified as cold-blooded 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 fish have warm-blooded characteristics, such as the opah. Swordfish and some sharks have circulatory mechanisms that keep their brains and eyes above ambient temperatures and thus increase their ability to detect and react to prey.[1][2][3] Tunas and some sharks have similar mechanisms in their muscles, improving their stamina when swimming at high speed.[4]
Heat generation
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Body heat is generated by metabolism.[5] This relates to the chemical reaction in cells that break down glucose into water and carbon dioxide, thereby producing adenosine triphosphate (ATP), a high-energy compound used to power other cellular processes. Muscle contraction is one such metabolic process generating heat energy,[6] and additional heat results from friction as blood circulates through the vascular system.
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.
In warm environments, these animals employ evaporative cooling to shed excess heat, either through
Defense against fungi
It has been hypothesized that warm-bloodedness evolved in mammals and birds as a defense against fungal infections. Very few fungi can survive the body temperatures of warm-blooded animals. By comparison, insects, reptiles, and amphibians are plagued by fungal infections.[8][9][10][11] Warm-blooded animals have a defense against pathogens contracted from the environment, since environmental pathogens are not adapted to their higher internal temperature.[12]
See also
References
Footnotes
Citations
- ^ Hot Eyes for Cold Fish – Wong 2005 (110): 2 – ScienceNOW
- S2CID 33962038.
- ^ "Warm eyes give deep-sea predators super vision". University of Queensland. 11 January 2005.
- ^ 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.
- PMID 29763018, retrieved 28 February 2024
- PMID 29086530. Retrieved 28 February 2024.
- PMID 33248118.
- ^ Dunn, Rob (2011). "Killer Fungi Made us Hotblooded". New Scientist. Retrieved 27 April 2016.(subscription required)
- doi:10.1086/644642
- PMID 19827944.
External links
