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Warm-blooded is an informal term referring to
animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
species
In biology, a species is the basic unit of 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 individuals of the appropriate s ...
which can maintain a body temperature higher than their environment. In particular,
homeothermic
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 ...
species maintain a stable body temperature by regulating metabolic processes. The only known living homeotherms are
birds
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
and
mammals
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
, and the only living
homeothermic
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 ...
lizard is the
Argentine black and white tegu
The Argentine black and white tegu (''Salvator merianae''), also known as the Argentine giant tegu, the black and white tegu, the huge tegu, is a species of lizard in the Family (biology), family Teiidae. The species is the largest of the "tegu l ...
. Some extinct reptiles such as
ichthyosaur
Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...
s,
pterosaurs
Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...
,
plesiosaurs
The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia.
Plesiosaurs first appeared ...
and some non-avian
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s are believed to have been homeotherms. Other species have various degrees of
thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
.
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 to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
.
*
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-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
(
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
: ἔνδον ''endon'' "within" θέρμη ''thermē'' "heat"). The opposite of endothermy is
ectothermy
An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life a ...
.
*
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 whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress. One of the most important stressors is temperature change, which can lead to alterations in membrane ...
. Mammals and birds are homeothermic.
*Tachymetabolism maintains a high "resting" metabolism (Greek: ταχύς ''tachys'' or ''tachus'' "fast, swift", ''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 mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...
s and small birds are
poikilothermic
A poikilotherm () is an animal whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress. One of the most important stressors is temperature change, which can lead to alterations in membrane ...
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 ἕτερος ''heteros'' "other" and θέρμη ''thermē'' "heat") is a physiological term for animals that vary between self-regulating their body temperature, and allowing the surrounding environment to ...
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
An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life a ...
,
poikilothermy
A poikilotherm () is an animal whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress. One of the most important stressors is temperature change, which can lead to alterations in membrane ...
, and
bradymetabolism
Bradymetabolism refers to organisms with a high active metabolism and a considerably slower resting metabolism.Bligh, J., and Johnson, K.G., 1973. Glossary for terms for thermal physiology. ''Journal of Applied Physiology'' 35(6):941–961. Bradym ...
), thus creating a broad spectrum of body temperature types. Some
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
have warm-blooded characteristics, such as the
opah
Opahs, also commonly known as moonfish, sunfish (not to be confused with Molidae), kingfish, redfin ocean pan are large, colorful, deep-bodied pelagic lampriform fishes comprising the small family Lampridae (also spelled Lamprididae).
The famil ...
.
Swordfish
Swordfish (''Xiphias gladius''), also known as broadbills in some countries, are large, highly migratory predatory fish characterized by a long, flat, pointed bill. They are a popular sport fish of the billfish category, though elusive. Swordfis ...
and some
shark
Sharks are a group of elasmobranch fish characterized by a 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 within the clade Selachimo ...
s have
circulatory
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
mechanisms that keep their
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
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 and conv ...
s above ambient temperatures and thus increase their ability to detect and react to
prey
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
. 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-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
. This refers to the chemical reactions
cell
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
s use to break down
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
into water and
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
and, in so doing, generate ATP (
adenosine triphosphate
Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms of ...
), 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 vascularized adipose tissue under the skin of all cetaceans, pinnipeds, penguins, and sirenians.
Description
Lipid-rich, collagen fiber-laced blubber comprises the hypodermis and covers the whole body, except for pa ...
in the case of mammals and
feather
Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premier ...
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 in warm-blooded animals. When the core body temperature drops, the shivering reflex is triggered to maintain homeostasis. Skeletal muscles begin to s ...
—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 mammals.
Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distr ...
(some mammals) or by
panting (many mammals and all birds)—in general, mechanisms not present in
poikilotherm
A poikilotherm () is an animal whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress. One of the most important stressors is temperature change, which can lead to alterations in membrane ...
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
A mesotherm (from Greek μέσος ''mesos'' "intermediate" and ''thermē'' "heat") is a type of animal with a thermoregulatory strategy intermediate to cold-blooded ectotherms and warm-blooded endotherms.
Definition
Mesotherms have two basic ch ...
*
Heterothermy
Heterothermy or heterothermia (from Greek ἕτερος ''heteros'' "other" and θέρμη ''thermē'' "heat") is a physiological term for animals that vary between self-regulating their body temperature, and allowing the surrounding environment to ...
*
Thermogenic plant Thermogenic plants have the ability to raise their temperature above that of the surrounding air. Heat is generated in the mitochondria, as a secondary process of cellular respiration called thermogenesis. Alternative oxidase and uncoupling proteins ...
*
Argentine black and white tegu#Endothermic behavior
References
External links
What is Warm Blooded??
{{DEFAULTSORT:Warm-Blooded
Animal physiology
Thermoregulation
ca:Sang calenta
it:Omeotermia
pt:Homeotermia