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Thermoregulation is the ability of an
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological ...

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 as its own body temperature, thus avoiding the need for internal thermoregulation. The internal thermoregulation process is one aspect of
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
: a state of dynamic stability in an organism's internal conditions, maintained far from
thermal equilibrium Two physical system A physical system is a collection of physical objects. In physics, it is a portion of the physical universe chosen for analysis. Everything outside the system is known as the environment (systems), environment. The enviro ...

thermal equilibrium
with its environment (the study of such processes in
zoology Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the Animal, animal kingdom, including the anatomy, structure, embryology, evolution, Biological class ...
has been called
physiological ecology Ecophysiology (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 approximately 10.7 mi ...
). If the body is unable to maintain a normal temperature and it increases significantly above normal, a condition known as
hyperthermia Hyperthermia, also known simply as overheating, is a condition where an individual's body temperature is elevated beyond normal due to failed thermoregulation. The person's body produces or absorbs more heat In thermodynamics, heat is ...
occurs. Humans may also experience lethal hyperthermia when the
wet bulb temperature The wet-bulb temperature (WBT) is the temperature read by a thermometer covered in water-soaked cloth ( wet-bulb thermometer) over which air is passed. At 100% relative humidity Humidity is the concentration of water vapor present in the air. ...
is sustained above for six hours. The opposite condition, when body temperature decreases below normal levels, is known as
hypothermia Hypothermia is defined as a body core temperature Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal ...
. It results when the homeostatic control mechanisms of heat within the body malfunction, causing the body to lose heat faster than producing it. Normal body temperature is around , and hypothermia sets in when the core body temperature gets lower than . Usually caused by prolonged exposure to cold temperatures, hypothermia is usually treated by methods that attempt to raise the body temperature back to a normal range. It was not until the introduction of
thermometer (mercury-in-glass thermometer) for measurement of room temperature. A thermometer is a device that temperature measurement, measures temperature or a temperature gradient A temperature gradient is a physical quantity that describes in which dir ...

thermometer
s that any exact data on the temperature of animals could be obtained. It was then found that local differences were present, since heat production and heat loss vary considerably in different parts of the body, although the circulation of the blood tends to bring about a mean temperature of the internal parts. Hence it is important to identify the parts of the body that most closely reflect the temperature of the
internal organ An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is the bulk of functional ...
s. Also, for such results to be comparable, the measurements must be conducted under comparable conditions. The
rectum The rectum is the final straight portion of the large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the re ...

rectum
has traditionally been considered to reflect most accurately the temperature of internal parts, or in some cases of sex or species, the
vagina In mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammalian female, femal ...

vagina
,
uterus The uterus (from Latin "uterus", plural ''uteri'') or womb () is the main female hormone-responsive, sex organ, secondary sex organ of the reproductive system in humans and most other mammals. Things occurring in the uterus are described with t ...

uterus
or
bladder The urinary bladder, or simply bladder, is a hollow muscular organ in humans and other vertebrates that stores urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ure ...
. Some animals undergo one of various forms of
dormancy Dormancy is a period in an organism's life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the pr ...
where the thermoregulation process temporarily allows the body temperature to drop, thereby conserving energy. Examples include
hibernating
hibernating
bear Bears are carnivora Carnivora is an order of placental Placentalia is one of the three extant subdivisions of the class of animals Mammalia Mammals (from Latin Latin (, or , ) is a classical language belonging to the Ita ...

bear
s and
torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμό ...
in
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.


Classification of animals by thermal characteristics


Endothermy vs. ectothermy

Thermoregulation in organisms runs along a spectrum from
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 to
ectotherm An ectotherm (from the 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 i ...
y.
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 ...
s create most of their heat via metabolic processes, and are colloquially referred to as warm-blooded. When the surrounding temperatures are cold, endotherms increase metabolic heat production to keep their body temperature constant, thus making the internal body temperature of an endotherm more or less independent of the temperature of the environment. One metabolic activity, in terms of generating heat, that endotherms are able to do is that they possess a larger number of mitochondria per cell than ectotherms, enabling them to generate more heat by increasing the rate at which they metabolize fats and sugars.
Ectotherm An ectotherm (from the 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 i ...
s use external sources of temperature to regulate their body temperatures. They are colloquially referred to as cold-blooded despite the fact that body temperatures often stay within the same temperature ranges as warm-blooded animals. Ectotherms are the opposite of endotherms when it comes to regulating internal temperatures. In ectotherms, the internal physiological sources of heat are of negligible importance; the biggest factor that enables them to maintain adequate body temperatures is due to environmental influences. Living in areas that maintain a constant temperature throughout the year, like the tropics or the ocean, has enabled ectotherms to develop a wide range of behavioral mechanisms that enable them to respond to external temperatures, such as sun-bathing to increase body temperature, or seeking the cover of shade to lower body temperature.


Ectotherms


Ectothermic cooling

*Vaporization: **
Evaporation Evaporation is a type of vaporization Vaporization (or vaporisation) of an element or compound is a phase transition from the liquid phase to vapor. There are two types of vaporization: evaporation and boiling. Evaporation is a surface phe ...

Evaporation
of sweat and other bodily fluids. *Convection: **Increasing blood flow to body surfaces to maximize heat transfer across the advective gradient. *Conduction: **Losing heat by being in contact with a colder surface. For instance: ***Lying on cool ground. ***Staying wet in a river, lake or sea. ***Covering in cool mud. *Radiation: **Releasing heat by radiating it away from the body.


Ectothermic heating (or minimizing heat loss)

*Convection: **Climbing to higher ground up trees, ridges, rocks. **Entering a warm water or air current. **Building an insulated nest or burrow. *Conduction: **Lying on a hot surface. *Radiation: **Lying in the sun (heating this way is affected by the body's angle in relation to the sun). **Folding skin to reduce exposure. **Concealing wing surfaces. **Exposing wing surfaces. *Insulation: **Changing shape to alter surface/volume ratio. **Inflating the body. To cope with low temperatures, 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 developed the ability to remain functional even when the water temperature is below freezing; some use natural
antifreeze An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression Freezing-point depression is a drop in the temperature at which a substance freezing, free ...

antifreeze
or
antifreeze proteins Antifreeze proteins (AFPs) or ice structuring proteins (ISPs) refer to a class of polypeptides Peptides (from Greek language Greek (modern , romanized: ''Elliniká'', Ancient Greek, ancient , ''Hellēnikḗ'') is an independent branch of ...
to resist ice crystal formation in their tissues.
Amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, ter ...
s and
reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile
s cope with heat gain by evaporative cooling and behavioral adaptations. An example of behavioral adaptation is that of a lizard lying in the sun on a hot rock in order to heat through radiation and conduction.


Endothermy

An endotherm is an animal that regulates its own body temperature, typically by keeping it at a constant level. To regulate body temperature, an organism may need to prevent heat gains in arid environments. Evaporation of water, either across respiratory surfaces or across the skin in those animals possessing
sweat glands Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin that produce sweat. Sweat glands are a type of exocrine gland, which are glands that produce and secrete substances onto an epithelial sur ...
, helps in cooling body temperature to within the organism's tolerance range. Animals with a body covered by fur have limited ability to sweat, relying heavily on panting to increase evaporation of water across the moist surfaces of the lungs and the tongue and mouth. Mammals like cats, dogs and pigs, rely on panting or other means for thermal regulation and have sweat glands only in foot pads and snout. The sweat produced on pads of paws and on palms and soles mostly serves to increase friction and enhance grip.
Bird 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 ...

Bird
s also counteract overheating by gular fluttering, or rapid vibrations of the gular (throat) skin.
Down feathers The down of bird Birds are a group of warm-blooded vertebrates constituting the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a ...
trap warm air acting as excellent insulators just as hair in mammals acts as a good insulator. Mammalian skin is much thicker than that of birds and often has a continuous layer of insulating fat beneath the dermis. In marine mammals, such as whales, or animals that live in very cold regions, such as the polar bears, this is called
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 ...
. Dense coats found in desert endotherms also aid in preventing heat gain such as in the case of the camels. A cold weather strategy is to temporarily decrease metabolic rate, decreasing the temperature difference between the animal and the air and thereby minimizing heat loss. Furthermore, having a lower metabolic rate is less energetically expensive. Many animals survive cold frosty nights through
torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμό ...
, a short-term temporary drop in body temperature. Organisms, when presented with the problem of regulating body temperature, have not only behavioural, physiological, and structural adaptations but also a feedback system to trigger these adaptations to regulate temperature accordingly. The main features of this system are ''stimulus, receptor, modulator, effector'' and then the feedback of the newly adjusted temperature to the ''stimulus.'' This cyclical process aids in homeostasis.


Homeothermy compared with poikilothermy

Homeothermy 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 ...
and
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 ...
refer to how stable an organism's deep-body temperature is. Most endothermic organisms are homeothermic, like
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s. However, animals with facultative endothermy are often poikilothermic, meaning their temperature can vary considerably. Most
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
are ectotherms, as most of their heat comes from the surrounding water. However, almost all fish are poikilothermic.


Vertebrates

By numerous observations upon
humans Humans (''Homo sapiens'') are the most abundant and widespread 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 speci ...
and other animals, John Hunter showed that the essential difference between the so-called warm-blooded and cold-blooded animals lies in observed constancy of the temperature of the former, and the observed variability of the temperature of the latter. Almost all birds and mammals have a high temperature almost constant and independent of that of the surrounding air (
homeothermy 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 ...
). Almost all other animals display a variation of body temperature, dependent on their surroundings (
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 ...
).


Brain control

Thermoregulation in both ectotherms and endotherms is controlled mainly by the
preoptic area The preoptic area is a region of the hypothalamus The hypothalamus (from Ancient Greek wikt:ὑπό, ὑπό, "under", and wikt:θάλαμος, θάλαμος, "chamber") is a portion of the brain that contains a number of small Nucleus (neuroan ...
of the
anterior hypothalamus The hypothalamus (from Ancient Greek wikt:ὑπό, ὑπό, "under", and wikt:θάλαμος, θάλαμος, "chamber") is a portion of the brain that contains a number of small Nucleus (neuroanatomy), nuclei with a variety of functions. One of ...
. Such
homeostatic In biology, homeostasis is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning for the organism and includes many variables, such ...
control is separate from the .


In birds and mammals

In cold environments, birds and mammals employ the following adaptations and strategies to minimize heat loss: # Using small smooth muscles (
arrector pili The arrector pili muscles, also knows as hair erector muscles, are small muscles attached to hair follicles The hair follicle is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with si ...
in mammals), which are attached to feather or hair shafts; this distorts the surface of the skin making feather/hair shaft stand erect (called
goose bumps Goose bumps, goosebumps or goose-pimples are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is tickled, cold , a common physiological response to cold, aiming to reduce the loss of bo ...

goose bumps
or pimples) which slows the movement of air across the skin and minimizes heat loss. # Increasing body size to more easily maintain core body temperature (warm-blooded animals in cold climates tend to be larger than similar species in warmer climates (see )) # Having the ability to store energy as fat for
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
# Have shortened extremities # Have in extremities – this is where the warm arterial blood travelling to the limb passes the cooler venous blood from the limb and heat is exchanged warming the venous blood and cooling the arterial (e.g.,
Arctic wolf The Arctic wolf (''Canis lupus arctos''), also known as the white wolf or polar wolf, is a subspecies of grey wolf native to Canada's Queen Elizabeth Islands The Queen Elizabeth Islands (french: Îles de la Reine-Élisabeth; formerly Parry ...
or penguins) In warm environments, birds and mammals employ the following adaptations and strategies to maximize heat loss: # Behavioural adaptations like living in burrows during the day and being nocturnal # Evaporative cooling by perspiration and panting # Storing fat reserves in one place (e.g., camel's hump) to avoid its insulating effect # Elongated, often vascularized extremities to conduct body heat to the air


In humans

As in other mammals, thermoregulation is an important aspect of human
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
. Most body heat is generated in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles. Humans have been able to adapt to a great diversity of climates, including hot humid and hot arid. High temperatures pose serious stresses for the human body, placing it in great danger of injury or even death. For example, one of the most common reactions to hot temperatures is heat exhaustion, which is an illness that could happen if one is exposed to high temperatures, resulting in some symptoms such as dizziness, fainting, or a rapid heartbeat. For humans,
adaptation In , adaptation has three related meanings. Firstly, it is the dynamic evolutionary process that fits s to their environment, enhancing their . Secondly, it is a state reached by the population during that process. Thirdly, it is a or adapti ...

adaptation
to varying climatic conditions includes both physiological mechanisms resulting from
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
and behavioural mechanisms resulting from conscious cultural adaptations.Harrison, G.A., Tanner, J.M., Pilbeam, D.R., & Baker, P.T. (1988) ''Human Biology: An introduction to human evolution, variation, growth, and adaptability''. (3rd ed). Oxford: Oxford University PressWeiss, M.L., & Mann, A.E. (1985) ''Human Biology and Behaviour: An anthropological perspective''. (4th ed). Boston: Little Brown The physiological control of the body's core temperature takes place primarily through the hypothalamus, which assumes the role as the body's "thermostat". This organ possesses control mechanisms as well as key temperature sensors, which are connected to nerve cells called thermoreceptors. Thermoreceptors come in two subcategories; ones that respond to cold temperatures and ones that respond to warm temperatures. Scattered throughout the body in both peripheral and central nervous systems, these nerve cells are sensitive to changes in temperature and are able to provide useful information to the hypothalamus through the process of negative feedback, thus maintaining a constant core temperature. There are four avenues of heat loss: evaporation, convection, conduction, and radiation. If skin temperature is greater than that of the surrounding air temperature, the body can lose heat by convection and conduction. But, if air temperature of the surroundings is greater than that of the skin, the body ''gains'' heat by convection and conduction. In such conditions, the only means by which the body can rid itself of heat is by evaporation. So, when the surrounding temperature is higher than the skin temperature, anything that prevents adequate evaporation will cause the internal body temperature to rise.Guyton & Hall (2006), pp. 891–892 During intense physical activity (e.g. sports), evaporation becomes the main avenue of heat loss. Humidity affects thermoregulation by limiting sweat evaporation and thus heat loss.Guyton, Arthur C. (1976) ''Textbook of Medical Physiology''. (5th ed). Philadelphia: W.B. Saunders


In reptiles

Thermoregulation is also an integral part of a reptile's life, specifically lizards such as the Microlophus occipitalis and '' Ctenophorus decresii'' who must change microhabitats to keep a constant body temperature. By moving to cooler areas when it is too hot and to warmer areas when it is cold, they can thermoregulate their temperature to stay within their necessary bounds.


In plants

Thermogenesis Thermogenesis is the process of heat production in organisms. It occurs in all warm-blooded animals, and also in a few species of thermogenic plants such as the Eastern skunk cabbage, the Voodoo lily (''Sauromatum venosum''), and the giant water ...
occurs in the flowers of many plants in the family
Araceae The Araceae are a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typica ...

Araceae
as well as in
cycad :''For the insect, see Cicada.'' Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious ...

cycad
cones. In addition, the
sacred lotus Sacred lotus may refer to: *''Nelumbo nucifera'', also known as "Indian lotus" **Padma (attribute), ''Nelumbo nucifera'' in Indian religions **Lotus throne in Buddhist and Hindu art *''Nymphaea caerulea'', the "blue lotus" in Ancient Egyptian relig ...

sacred lotus
(''Nelumbo nucifera'') is able to thermoregulate itself, remaining on average above air temperature while flowering. Heat is produced by breaking down the starch that was stored in their roots, which requires the consumption of oxygen at a rate approaching that of a flying
hummingbird Hummingbirds are Bird, birds native to the Americas and comprise the Family (biology), biological family Trochilidae. With about 360 species, they occur from Alaska to Tierra del Fuego, but the vast majority of the species are found in the tropi ...

hummingbird
. One possible explanation for plant thermoregulation is to provide protection against cold temperature. For example, the skunk cabbage is not frost-resistant, yet it begins to grow and flower when there is still snow on the ground. Another theory is that thermogenicity helps attract pollinators, which is borne out by observations that heat production is accompanied by the arrival of beetles or flies. Some plants are known to protect themselves against colder temperatures using
antifreeze protein Antifreeze proteins (AFPs) or ice structuring proteins (ISPs) refer to a class of polypeptides produced by certain animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological ...
s. This occurs in
wheat Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. The many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat Common wheat (''Triticum aestivum'' ...

wheat
(''Triticum aestivum),''
potato The potato is a starch#Food, starchy tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial plant, perennial in the nightshade family Solanaceae. Wild potato species can be found thro ...

potato
es (''Solanum tuberosum'') and several other
angiosperm Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ...

angiosperm
species.


Behavioral temperature regulation

Animals other than humans regulate and maintain their body temperature with physiological adjustments and behavior. Desert lizards are ectotherms and so unable to metabolically control their temperature but can do this by altering their location. They may do this, in the morning only by raising their head from its burrow and then exposing their entire body. By basking in the sun, the lizard absorbs solar heat. It may also absorb heat by conduction from heated rocks that have stored radiant solar energy. To lower their temperature, lizards exhibit varied behaviors. Sand seas, or
erg The erg is a unit of energy equal to 10−7joule The joule ( ; symbol: J) is a SI derived unit, derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work (physics), work done on) an objec ...
s, produce up to , and the sand lizard will hold its feet up in the air to cool down, seek cooler objects with which to contact, find shade or return to their burrow. They also go to their burrows to avoid cooling when the sun goes down or the temperature falls. Aquatic animals can also regulate their temperature behaviorally by changing their position in the thermal gradient. Animals also engage in kleptothermy in which they share or even steal each other's body warmth. In endotherms such as
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 birds (such as the
mousebird The mousebirds are bird 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), biolog ...

mousebird
and
emperor penguin The emperor penguin (''Aptenodytes forsteri'') is the tallest and heaviest of all living penguin species and is Endemism in birds, endemic to Antarctica. The male and female are similar in plumage and size, reaching in length and weighing fr ...

emperor penguin
) it allows the sharing of body heat (particularly amongst juveniles). This allows the individuals to increase their thermal inertia (as with gigantothermy) and so reduce
heat In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these ...

heat
loss. Some ectotherms share burrows of ectotherms. Other animals exploit
termite Termites are Eusociality, eusocial insects that are classified at the Taxonomy (biology), taxonomic rank of infraorder Isoptera, or alternatively as Taxonomic rank#All ranks, epifamily Termitoidae, within the order Blattodea (along with cockroa ...

termite
mounds. Some animals living in cold environments maintain their body temperature by preventing heat loss. Their fur grows more densely to increase the amount of . Some animals are regionally heterothermic and are able to allow their less insulated extremities to cool to temperatures much lower than their core temperature—nearly to . This minimizes heat loss through less insulated body parts, like the legs, feet (or hooves), and nose. Different species of Sonoran Desert Drosophila will exploit different species of cacti based on the thermotolerance differences between species and hosts. For example, Drosophila ''mettleri'' is found in cacti like the Saguaro and Senita; these two cacti remain cool by storing water. Over time, the genes selecting for higher heat tolerance were reduced in the population due to the cooler host climate the fly is able to exploit. Some flies, such as '','' lay their eggs en masse. The resulting group of larvae, depending on its size, is able to thermoregulate and keep itself at the optimum temperature for development.


Hibernation, estivation and daily torpor

To cope with limited food resources and low temperatures, some mammals
hibernate Hibernation is a state of minimal activity and metabolic depression. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate Metabolism (, from el, μετα ...

hibernate
during cold periods. To remain in "stasis" for long periods, these animals build up
brown fat Brown adipose tissue (BAT) or brown fat makes up the adipose organ together with white adipose tissue White adipose tissue (WAT) or white fat is one of the two types of adipose tissue Adipose tissue, body fat, or simply fat is a loose connective ...
reserves and slow all body functions. True hibernators (e.g., groundhogs) keep their body temperatures low throughout hibernation whereas the
core temperature Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...
of false hibernators (e.g., bears) varies; occasionally the animal may emerge from its den for brief periods. Some bats are true hibernators and rely upon a rapid, non-shivering thermogenesis of their brown fat deposit to bring them out of hibernation. is similar to hibernation, however, it usually occurs in hot periods to allow animals to avoid high temperatures and
desiccation Desiccation (from Latin de- "thoroughly" + siccare "to dry") is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its lo ...
. Both terrestrial and aquatic invertebrate and vertebrates enter into estivation. Examples include lady beetles (''
Coccinellidae Coccinellidae () is a widespread family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its membe ...

Coccinellidae
''), ,
crocodile Crocodiles (family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society. I ...

crocodile
s,
salamander Salamanders are a group of amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most spe ...

salamander
s,
cane toad The cane toad (''Rhinella marina''), also known as the giant neotropical toad or marine toad, is a large, Terrestrial animal, terrestrial true toad native to South America, South and mainland Central America, but which has been Introduced specie ...

cane toad
s, and the . Daily
torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμό ...
occurs in small endotherms like
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
hummingbirds Hummingbirds are Bird, birds native to the Americas and comprise the Family (biology), biological family Trochilidae. With about 360 species, they occur from Alaska to Tierra del Fuego, but the vast majority of the species are found in the tropi ...
, which temporarily reduces their high metabolic rates to conserve energy.


Variation in animals


Normal human temperature

Previously, average oral temperature for healthy adults had been considered , while normal ranges are . In Poland and Russia, the temperature had been measured
axilla The axilla (also, armpit, underarm or oxter) is the area on the human body directly under the joint where the arm connects to the shoulder. It also contains many sweat glands. In humans, the formation of body odor happens mostly in the armpit. T ...

axilla
rily (under the arm). was considered "ideal" temperature in these countries, while normal ranges are . Recent studies suggest that the average temperature for healthy adults is (same result in three different studies). Variations (one
standard deviation In statistics, the standard deviation is a measure of the amount of variation or statistical dispersion, dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected v ...

standard deviation
) from three other studies are: * * for males,
for females * Measured temperature varies according to thermometer placement, with rectal temperature being higher than oral temperature, while axillary temperature is lower than oral temperature. The average difference between oral and axillary temperatures of
India India, officially the Republic of India (Hindi Hindi (Devanagari: , हिंदी, ISO 15919, ISO: ), or more precisely Modern Standard Hindi (Devanagari: , ISO 15919, ISO: ), is an Indo-Aryan language spoken chiefly in Hindi Belt, ...

India
n children aged 6–12 was found to be only 0.1 °C (standard deviation 0.2 °C), and the mean difference in
Maltese Maltese may refer to: * Someone or something of, from, or related to Malta * Maltese alphabet * Maltese cuisine * Maltese culture * Maltese language, the Semitic language spoken by Maltese people * Maltese people, people from Malta or of Maltese ...

Maltese
children aged 4–14 between oral and axillary temperature was 0.56 °C, while the mean difference between rectal and axillary temperature for children under 4 years old was 0.38 °C.


Variations due to circadian rhythms

In humans, a diurnal variation has been observed dependent on the periods of rest and activity, lowest at 11 p.m. to 3 a.m. and peaking at 10 a.m. to 6 p.m.
Monkey Monkey is a common name that may refer to most mammals of the infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structur ...

Monkey
s also have a well-marked and regular diurnal variation of body temperature that follows periods of rest and activity, and is not dependent on the incidence of day and night;
nocturnal Nocturnality is an animal behavior Ethology is the scientific Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was original ...
monkeys reach their highest body temperature at night and lowest during the day. Sutherland Simpson and J.J. Galbraith observed that all nocturnal animals and birds – whose periods of rest and activity are naturally reversed through habit and not from outside interference – experience their highest temperature during the natural period of activity (night) and lowest during the period of rest (day). Those diurnal temperatures can be reversed by reversing their daily routine. In essence, the temperature curve of
diurnal Diurnal ("daily Daily or The Daily may refer to: Journalism * Daily newspaper A newspaper is a Periodical literature, periodical publication containing written News, information about current events and is often typed in black ink with a ...
birds is similar to that of humans and other homoeothermal animals, except that the maximum occurs earlier in the afternoon and the minimum earlier in the morning. Also, the curves obtained from rabbits,
guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy (), is a species of rodent Rodents (from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the I ...

guinea pig
s, and dogs were quite similar to those from humans. These observations indicate that body temperature is partially regulated by
circadian rhythm A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., endogenous Endogenous subst ...

circadian rhythm
s.


Variations due to human menstrual cycles

During the
follicular phase The follicular phase, also known as the preovulatory phase or proliferative phase, is the phase of the estrous cycle (or, in primates for example (humans, monkey and great apes), the menstrual cycle) during which ovarian follicle, follicles in t ...
(which lasts from the first day of
menstruation Menstruation (also known as a period and many other Colloquialism, colloquial terms) is the regular discharge of blood and Mucous membrane, mucosal tissue from the endometrium, inner lining of the uterus through the vagina. The menstrual cycl ...
until the day of
ovulation Ovulation is the release of egg An egg is the organic vessel containing the in which an develops until it can survive on its own, at which point the animal hatches. An egg results from of an . Most s, (excluding s), and lay eggs, alth ...

ovulation
), the average
basal body temperature Basal body temperature (BBT or BTP) is the lowest body temperature attained during rest (usually during sleep). It is usually estimated by a temperature measurement immediately after awakening and before any physical activity has been undertaken. ...
in women ranges from . Within 24 hours of ovulation, women experience an elevation of due to the increased metabolic rate caused by sharply elevated levels of
progesterone Progesterone (P4) is an endogenous Endogenous substances and processes are those that originate from within a system such as an organism, Tissue (biology), tissue, or Cell (biology), cell. Endogenous substances and processes contrast with exo ...

progesterone
. The basal body temperature ranges between throughout the
luteal phase The menstrual cycle is on average 28 days in length. It begins with menses (day 1-7) during the follicular phase (day 1-14) and followed by ovulation (day 14) and ending with the luteal phase (day 14-28). Unlike the follicular phase which can vary ...
, and drops down to pre-ovulatory levels within a few days of menstruation. Women can chart this phenomenon to determine whether and when they are ovulating, so as to aid conception or contraception.


Variations due to fever

Fever Fever, also referred to as pyrexia, is defined as having a temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on th ...

Fever
is a regulated elevation of the set point of core temperature in the
hypothalamus The hypothalamus (from Ancient Greek wikt:ὑπό, ὑπό, "under", and wikt:θάλαμος, θάλαμος, "chamber") is a portion of the brain that contains a number of small Nucleus (neuroanatomy), nuclei with a variety of functions. One of ...

hypothalamus
, caused by circulating pyrogens produced by the immune system. To the subject, a rise in core temperature due to fever may result in feeling cold in an environment where people without fever do not.


Variations due to biofeedback

Some monks are known to practice
Tummo In Tibetan Buddhism, ''tummo'' (; sa, चण्डाली, caṇḍālī) is the fierce goddess of heat and passion. Tummo is found in the Mahasiddha Krishnacarya and the ''Hevajra, Hevajra Tantra'' texts. Tummo is also a Tibetan tantric p ...
,
biofeedback Biofeedback is the process of gaining greater awareness of many physiological functions of one's own body, commercially by using electronic or other instruments, and with a goal of being able to manipulate the body's systems at will. Humans cond ...

biofeedback
meditation Meditation is a practice where an individual uses a technique – such as mindfulness Mindfulness is the practice of purposely bringing one's attention in the present moment without evaluation,Mindfulness Training as a Clinical Interventio ...

meditation
techniques, that allow them to raise their body temperatures substantially.


Low body temperature increases lifespan

It has been theorized that low body temperature may increase lifespan. In 2006, it was reported that transgenic mice with a body temperature lower than normal mice lived longer than normal mice. This mechanism is due to overexpressing the uncoupling protein 2 in hypocretin neurons (Hcrt-UCP2), which elevated hypothalamic temperature, thus forcing the
hypothalamus The hypothalamus (from Ancient Greek wikt:ὑπό, ὑπό, "under", and wikt:θάλαμος, θάλαμος, "chamber") is a portion of the brain that contains a number of small Nucleus (neuroanatomy), nuclei with a variety of functions. One of ...

hypothalamus
to lower body temperature. Lifespan was increased by 12% and 20% for males and females, respectively. The mice were fed ''
ad libitum In music, biology, and drama, the phrase ''ad libitum'' (; 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 ...
''. The effects of such a genetic change in body temperature on longevity is more difficult to study in humans; in 2011, the UCP2 genetic alleles in humans were associated with obesity.


Limits compatible with life

There are limits both of heat and cold that an endothermic animal can bear and other far wider limits that an
ectothermic ''Junonia lemonias'' is basking under the sun. An ectotherm (from the Ancient Greek, Greek ἐκτός (''ektós'') "outside" and θερμός (''thermós'') "hot") is an organism in which internal physiological sources of heat are of relatively ...
animal may endure and yet live. The effect of too extreme a cold is to decrease
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
, and hence to lessen the production of heat. Both
catabolic Catabolism () is the set of metabolic pathways that breaks down molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an ...
and
anabolic Anabolism () is the set of metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation ...
pathways share in this metabolic depression, and, though less energy is used up, still less energy is generated. The effects of this diminished metabolism become telling on the
central nervous system The central nervous system (CNS) is the part of the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecu ...

central nervous system
first, especially the
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
and those parts concerning consciousness; both
heart rate Heart rate is the speed of the heartbeat Heartbeat or heartbeats may refer to: Physiology *Cardiac cycle, of the heart *Contraction of the cardiac muscle, muscles of the heart, or a perceived effect of it, such as: **Heart sounds, the noises gene ...

heart rate
and
respiration rate The respiration rate is a parameter which is used in ecological and agronomical modeling. In theoretical production ecology and aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the farming of fish, c ...
decrease; judgment becomes impaired as drowsiness supervenes, becoming steadily deeper until the individual loses consciousness; without medical intervention,
death Death is the permanent, irreversible cessation of all biological functions that sustain a living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objects and dead organi ...

death
by
hypothermia Hypothermia is defined as a body core temperature Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal ...
quickly follows. Occasionally, however,
convulsion A convulsion is a medical condition where body muscles Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amin ...
s may set in towards the end, and death is caused by
asphyxia Asphyxia or asphyxiation is a condition of deficient supply of oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an ...
. In experiments on cats performed by Sutherland Simpson and Percy T. Herring, the animals were unable to survive when rectal temperature fell below . At this low temperature, respiration became increasingly feeble; heart-impulse usually continued after respiration had ceased, the beats becoming very irregular, appearing to cease, then beginning again. Death appeared to be mainly due to
asphyxia Asphyxia or asphyxiation is a condition of deficient supply of oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an ...
, and the only certain sign that it had taken place was the loss of knee-jerks. However, too high a temperature speeds up the metabolism of different tissues to such a rate that their metabolic capital is soon exhausted. Blood that is too warm produces
dyspnea Shortness of breath (SOB), also known as dyspnea (BrE British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codificat ...
by exhausting the metabolic capital of the respiratory centre; heart rate is increased; the beats then become arrhythmic and eventually cease. The central nervous system is also profoundly affected by
hyperthermia Hyperthermia, also known simply as overheating, is a condition where an individual's body temperature is elevated beyond normal due to failed thermoregulation. The person's body produces or absorbs more heat In thermodynamics, heat is ...
and
delirium Delirium (also known as acute confusional state) is an organically caused decline from a previous baseline mental functioning, that develops over a short period of time, typically hours to days. Delirium is a syndrome A syndrome is a set of me ...
, and convulsions may set in. Consciousness may also be lost, propelling the person into a
coma A coma is a deep state of prolonged unconsciousness Unconsciousness is a state which occurs when the ability to maintain an consciousness, awareness of self and environment is lost. It involves a complete, or near-complete, lack of responsive ...
tose condition. These changes can sometimes also be observed in patients suffering from an acute
fever Fever, also referred to as pyrexia, is defined as having a temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on th ...

fever
.
Mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
ian muscle becomes rigid with heat rigor at about 50 °C, with the sudden rigidity of the whole body rendering life impossible. H.M. Vernon performed work on the death temperature and paralysis temperature (temperature of heat rigor) of various animals. He found that species of the same
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
showed very similar temperature values, those from the
Amphibia Amphibians are ectotherm File:Junonia lemonias DSF by Kadavoor.JPG, ''Junonia lemonias'' is basking under the sun. An ectotherm (from the Ancient Greek, Greek ἐκτός (''ektós'') "outside" and θερμός (''thermós'') "hot") is an ...

Amphibia
examined being 38.5 °C,
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
39 °C,
reptiles Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptiles
45 °C, and various
mollusc Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number ...
s 46 °C. Also, in the case of
pelagic The pelagic zone consists of the water column A water column is a concept Concepts are defined as abstract ideas A mental representation (or cognitive representation), in philosophy of mind Philosophy of mind is a branch of philosophy ...
animals, he showed a relation between death temperature and the quantity of solid constituents of the body. In higher animals, however, his experiments tend to show that there is greater variation in both the chemical and physical characteristics of the
protoplasmProtoplasm (/prəʊtə(ʊ)ˌplaz(ə)m/, plural protoplasms) is the living part of a cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or ...

protoplasm
and, hence, greater variation in the extreme temperature compatible with life.


Arthropoda

The maximum temperatures tolerated by certain
thermophilic 300px, Thermophiles produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are arch ...
arthropods exceeds the lethal temperatures for most vertebrates. The most heat-resistant insects are three genera of desert ants recorded from three different parts of the world. The ants have developed a lifestyle of scavenging for short durations during the hottest hours of the day, in excess of , for the carcasses of insects and other forms of life which have succumbed to heat stress. In April 2014, the South Californian mite '' Paratarsotomus macropalpis'' has been recorded as the world's fastest land animal relative to body length, at a speed of 322 body lengths per second. Besides the unusually great speed of the mites, the researchers were surprised to find the mites running at such speeds on concrete at temperatures up to , which is significant because this temperature is well above the lethal limit for the majority of animal species. In addition, the mites are able to stop and change direction very quickly. Spiders like ''Nephila pilipes'' exhibits active thermal regulation behavior. During high temperature sunny days, it aligns its body with the direction of sunlight to reduce the body area under direct sunlight.


See also

*Human body temperature *Innate heat *Insect thermoregulation *Thermal neutral zone


References


Further reading

*
full pdf
* This cites work o
Simpson & Galbraith

Other Internet Archive listings

see Table of Contents link
(Previously ''Guyton's Textbook of Medical Physiology''. Earlier editions back to at least 5th edition 1976, contain useful information on the subject of thermoregulation, the concepts of which have changed little in that time). * *
link to abstract
* * * * * * *Weldon Owen Pty Ltd. (1993). ''Encyclopedia of animals – Mammals, Birds, Reptiles, Amphibians.'' Reader's Digest Association, Inc. Pages 567–568. .


External links

*
Royal Institution Christmas Lectures 1998
* * {{Authority control Thermoregulation, Human homeostasis Animal physiology Heat transfer Articles containing video clips Mathematics in medicine