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Warm-blooded is an informal term referring to
animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animal
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
which can maintain a body temperature higher than their environment. In particular,
homeothermic Homeothermy, homothermy or homoiothermy is thermoregulation Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system ...
species maintain a stable body temperature by regulating metabolic processes. The only known living homeotherms are
birds Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

birds
and
mammals Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the R ...
, though
ichthyosaur Ichthyosaurs (Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Myce ...
s,
pterosaurs Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") were flying reptile Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes ...

pterosaurs
,
plesiosaurs The Plesiosauria (; Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 ...
and some non-avian
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 annum, million years ago, although the exact origin and timing of the evolution ...

dinosaur
s are believed to have been homeotherms. Other species have various degrees of
thermoregulation Thermoregulation is the ability of an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxo ...
. Animal body temperature control varies by species, so the terms "warm-blooded" and " cold-blooded" (though still in everyday use) suggest a false idea of there being only two categories of body temperature control, and are no longer used scientifically.


Terminology

In general, warm-bloodedness refers to three separate categories of
thermoregulation Thermoregulation is the ability of an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxo ...
. *
Endotherm An endotherm (from Greek ἔνδον ''endon'' "within" and θέρμη ''thermē'' "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily functions inste ...
y is the ability of some creatures to control their body temperatures through internal means such as muscle shivering or increasing their
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
(
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
: ἔνδον ''endon'' "within" θέρμη ''thermē'' "heat"). The opposite of endothermy is ectothermy. *
Homeotherm Homeothermy, homothermy or homoiothermy is thermoregulation that maintains a stable internal body temperature regardless of external influence. This internal body temperature is often, though not necessarily, higher than the immediate environmen ...
y maintains a stable internal body temperature regardless of external influence and temperatures. The stable internal temperature is often higher than the immediate environment (Greek: ὅμοιος ''homoios'' "similar", θέρμη ''thermē'' "heat"). The opposite is
poikilothermy A poikilotherm () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellula ...
. Mammals and birds are homeothermic. *Tachymetabolism maintains a high "resting" metabolism (Greek: ταχύς ''tachys/tachus'' "fast, swift", μεταβάλλειν ''metaballein'' "turn quickly"). 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 bradymetabolic creatures. Tachymetabolic creatures have greater difficulty dealing with a scarcity of food.


The variety of thermoregulation types

A large proportion of the creatures traditionally called "warm-blooded", like birds and mammals, fit all three of these categories (i.e., they are endothermic, homeothermic, ''and'' tachymetabolic). However, over the past 30 years, studies in the field of animal thermophysiology have revealed many species belonging to these two groups that do not fit all these criteria. For example, many
bat Bats are mammal Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the po ...

bat
s and small birds are
poikilothermic A poikilotherm () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellula ...
and bradymetabolic when they sleep for the night (or, in nocturnal species, for the day). For these creatures, the term
heterothermy Heterothermy or heterothermia (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approx ...
was coined. Further studies on animals that were traditionally assumed to be cold-blooded have shown that most creatures incorporate different variations of the three terms defined above, along with their counterparts ( ectothermy,
poikilothermy A poikilotherm () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellula ...
, and bradymetabolism), thus creating a broad spectrum of body temperature types. Some
fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish
have warm-blooded characteristics, such as the
opah Opahs, also commonly known as moonfish, sunfish (not to be confused with Molidae The Molidae comprise the family of the molas or ocean sunfishes, unusual fish whose bodies come to an end just behind the dorsal fin, dorsal and anal fins, givin ...

opah
.
Swordfish Swordfish (''Xiphias gladius''), also known as broadbills in some countries, are large, highly migratory predatory fish Predatory fish are fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), lim ...

Swordfish
and some
shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified withi ...

shark
s have circulatory mechanisms that keep their
brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tis ...

brain
s and
eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light L ...

eye
s above ambient temperatures and thus increase their ability to detect and react to
prey Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical env ...

prey
. Tunas and some sharks have similar mechanisms in their muscles, improving their stamina when swimming at high speed.


Heat generation

Body heat is generated by
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
. This refers to the chemical reactions cells use to break down
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
into water and
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
and, in so doing, generate ATP (
adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properti ...

adenosine triphosphate
), a high-energy compound used to power other cellular processes. Muscle contraction is a type of metabolic process that generates heat energy, and heat is also generated through friction when blood flows through the circulatory 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 most organisms, this heat is simply lost to the environment. However, endothermic homeotherms (the animals generally characterized as "warm-blooded") both produce more heat and have better ways to retain and regulate it than other animals. They have a higher basal metabolic rate, and also a greater capacity to increase their metabolic rate when engaged in strenuous activity. They usually have well-developed insulation in order to retain body heat, fur and
blubber Blubber is a thick layer of vascular The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an Biological system, organ system that permits ...
in the case of mammals and
feather Feathers are epidermal growths that form a distinctive outer covering, or plumage Plumage ( "feather") is a layer of feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on dinosaurs, both avi ...

feather
s in birds. When this insulation is insufficient to maintain body temperature, they may resort to
shivering Shivering (also called shuddering) is a bodily function in response to cold and extreme fear Fear is an intensely unpleasant emotion Emotions are mental state, psychological states brought on by neurophysiology, neurophysiological change ...
—rapid muscle contractions that quickly use up ATP, thus stimulating cellular metabolism to replace it and consequently produce more heat. In general, in hot environments, they use evaporative cooling to shed excess heat, either by
sweating Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), cla ...
(some mammals) or by panting (many mammals and all birds)—in general, mechanisms not present in
poikilotherm A poikilotherm () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellula ...
s.


Defense against fungi

It has been hypothesized that warm-bloodedness evolved in mammals and birds because it provided 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. Mammals and other warm-blooded animals pick up pathogens from other hosts. Those pathogens from the hosts are already adapted to the high temperature. Warm blooded animals have a defense against pathogens picked up from the environment since the environmental pathogens are not used to the difference in temperature.


See also

* Mesotherm *
Heterothermy Heterothermy or heterothermia (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approx ...
* Argentine black and white tegu#Warm-bloodedness


References


External links


What is Warm Blooded??
{{DEFAULTSORT:Warm-Blooded Animal physiology Thermoregulation ca:Sang calenta it:Omeotermia pt:Homeotermia