- Heterothermic
Heterothermic (from Greek: "hetero" = "other" "thermy" = "heat.") is a physiological term referring to a unique case of
poikilothermy . Heterothermic creatures arehomeothermic for a portion of the day, or year. More often than not, it is usually used as a way to dissociate the fluctuating metabolic rates seen in some small mammals and birds (e.g.bats andhummingbirds ), from those of traditional cold blooded animals. In manybat species, body temperature and metabolic rate, are elevated only during activity. When at rest, these animals reduce theirmetabolism s drastically, which results in their body temperature dropping to that of the surrounding environment. This makes themhomeothermic when active, andpoikilothermic when at rest.Note: Strictly speaking, heterothermy is just a variant of
poikilothermy , as the internal body temperature still varies.Regional heterothermy
Regional heterothermy is a far more specific type of heterothermy. It describes organisms that are able to maintain different temperature "zones" in different regions of the body. This usually occurs in the limbs, and is made possible through the use of counter current heat exchangers, such as the
rete mirabile found in tuna and certain birds. These exchangers equalise the temperature between hot arterial blood going out to the extremities and cold venous blood coming back, thus reducing heat loss. Penguins and many arcticbirds use these exchangers to keep their feet at roughly the same temperature as the surrounding ice. This keeps thebirds from getting stuck on an ice sheet. Other animals, like theLeatherback Sea Turtle , use the heat exchangers to gather, and retain heat generated by their muscular flippers. There are even someinsect s which possess this mechanism, the best-known example beingbumblebee s, which exhibit counter current heat exchange at the point of constriction between themesosoma ("thorax") andmetasoma ("abdomen"); heat is retained in the thorax and lost from the abdomen. Using a very similar mechanism, the internal temperature of ahoneybee 's thorax can exceed 45C while in flight.References
External links
* [http://www.bio.davidson.edu/Courses/anphys/1999/McKinley/thermobio.html Thermobiology of bats]
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