Thermoregulation
In biology, thermoregulation is understood as the more or less great independence of an organism's body temperature from the outside world. A distinction can be made between thermoconforms ( poikilothermic = cold- blooded animals) and thermoregulators ( homoiothermic = cold-blooded animals).
The terms warm-blooded and cold-blooded animals are no longer used in this context and are only used in relation to horse breeds , in which the terms do not refer to body temperature but to temperament.
Explanation of terms
There are two ways of classifying the types of regulation. The first classification is based on how the body temperature changes compared to the outside temperature:
- Animals that keep their body temperature at a constantly high, constant level and can regulate it within narrow limits are referred to as homoiothermic or homeothermic . This includes almost all mammals and all birds .
- As poikilothermic (from the Greek: partly) all other animals are called, the body temperature of the outside temperature is more or less follows passively , that changes depending on the ambient temperature. These include the lower vertebrates , namely fish , amphibians and reptiles , as well as invertebrates .
- Heterothermal are animals that can vary their body temperature by a few degrees, but only briefly and limited to certain body sections, but not within narrow limits. They are still subdivided into temporary heterotherms and regional heterotherms. The echidna (Echidna) and the platypus (both monotremes ) are temporary heterotherm, that is, their body temperature varies with time very strong. Temporal variations in body temperature can also be found in some desert-dwelling mammals and the Asian elephant and also in many insects and in the python snake. Bees and bumblebees can bring their thorax to operating temperature by trembling their muscles . They have a mechanism ( countercurrent principle ) that prevents the generated heat from flowing into the abdomen . This would make them an example of regionally heterothermal animals.
The second, but problematic, classification asks about the origin of body heat, whereby
- endothermic animals produce their own heat and
- ectothermic animals receive almost all of their body heat from their surroundings.
This classification makes sense insofar as there are virtually no temperature fluctuations in the habitat of a poikilothermal deep-sea fish, for example. Therefore his body temperature remains constant within very narrow limits, so to speak homoiothermal (uniformly warm). Some poikilothermal deep-sea fish , such as the tuna , can have a temperature 10–15 K higher than the water temperature during movement due to their muscle work , so they do not have the same body temperature as their surroundings. In contrast, a hummingbird as a homoiothermic animal falls into a torpor at night and has a temperature 10–20 K lower than during the day.
However, endothermic and exothermic are clearly defined terms in physical chemistry and "ectothermic" is predestined to be confused with "exothermic". In addition, cold-blooded animals naturally also produce warmth during their life processes, but they do not have the same mechanisms as animals of the same temperature to do this sufficiently and constantly.
Despite the problems described, the terms homoiothermic and endothermic or poikilothermic and ectothermic are often mixed and used synonymously in biology . The reason for this is likely to be the great variety of thermoregulatory performance of animals. The terms homoiotherm and poikilotherm describe this only approximately. The assignment of a group of animals is not easy, as one often comes across smooth transitions.
| Thermal conformers | Thermoregulator | ||
|---|---|---|---|
| poikilotherm | homoiotherm | ||
| ectothermic | endothermic | ||
| (in cold blood) | (warm blooded) | ||
| heterothermal | |||
In the following, only the terms homoiotherm and poikilotherm are used.
Body core and body shell
When speaking of body temperature in general, one is not making an inadmissible generalization only when speaking of the temperature inside the body. The body temperature does not exist. If you measure at different points, you get different values. [Don't forget: If you measure at different times, different values result (even for the core) ( see also chronobiology )].
The temperature of different parts of the body that are not part of the core depends on the ambient temperature and muscle activity. With homoiotherms, the temperature is only kept constant inside the body, which is why your body temperature can be determined most precisely via rectal temperature measurement. The body shell opposes the body core.
The organs with high energy turnover ( heart , liver , kidneys and brain ), which are the places where heat is generated, are located in the core of the body . Their mass makes up only 8% of the body mass in humans, but their share in the energy expenditure of a resting person is more than 70%. Skin and muscles, on the other hand, make up 52% of the body's mass, but only provide 18% of the total heat when at rest. When moving, however, more heat is generated in the body shell; then their proportion exceeds that of the nucleus by far.
As isotherms lines is called with the same temperature. The body shell is therefore not a firmly defined area, but depends on the ambient temperature. The changing blood flow to the individual parts of the body is responsible for the shift in the isotherms. In humans, for example, the blood flow to the fingers is very variable; it can fluctuate by a factor of 600. If the fingers are only weakly supplied with blood at a low ambient temperature, the temperature difference between them and their surroundings is no longer as great and they lose less heat. Changing blood flow to the body shell is an important temperature-regulating measure that is used by all species and in both directions - against hypothermia and overheating. The body temperature of a sled dog does not show the same values everywhere either. The differences are achieved through all sorts of measures: changes in blood flow, countercurrent principle, fat deposits, insulating fur.
Sense of thermoregulation
In poikilothermic animals, the rate of metabolism is just as temperature-dependent as the rate of reaction in biochemical systems ( Van-'t-Hoff rule ), while in homoiothermic animals it rises to a critical point with increasing outside temperature (from this point it becomes independent). If the outside temperature falls below a critical point, a homoiothermic animal has to increase its metabolism. Maintaining a constant body temperature is expensive: Homoiotherms need more food than Poikilotherms for the same “work unit”.
However, the increased effort required to maintain a constant body temperature is offset by a benefit, because enzymatic metabolic reactions are highly temperature-dependent. While poikilothermic animal species need certain outside temperature ranges to live, homoiothermic animals such as mammals and birds are far less dependent on it due to their ability to regulate temperature and are able to live and metabolic reactions also in more moderate latitudes or even subpolar and polar zones . Although they need a larger amount of food than poikilothermic animals, they have more options - their ecological potential is greater.
The body temperature of a homoiotherm is to be understood as a control cycle. This means that there is a setpoint that is constantly compared with an actual value and that has actuators that adjust the actual value to the setpoint if it deviates.
Regulation of the temperature setpoint in homoiothermal mammals
It is not a single region of the nervous system that functions as the sole thermoregulation center, but hierarchically structured structures: the spinal cord and the brain stem can already perceive gross changes in body temperature and initiate regulation. This can be seen when nerve tracts from higher up are interrupted and a rough temperature control still takes place. However, only when these deeper-lying areas of the central nervous system are connected to the praeoptica region of the hypothalamus , the thermoregulation becomes precise, especially with changes in the ambient temperature and physical exertion. There, the actual core body temperature is more precisely perceived directly. B. from heat and cold receptors from the skin of the whole body together.
The temperature information from the periphery is compared with the central temperature information and integrated; This results in a suitable thermoregulatory response, ultimately controlled from here, in the direction of heat loss (peripheral vasodilation and skin warming, sweating, panting in the dog, etc.) or in the direction of heat production and saving (peripheral vasoconstriction and skin cold, shivering, etc.). Normal pyrogen-induced fever reactions are also only possible with an intact praeoptica region of the hypothalamus.
There are various neurons in the praeoptica region of the hypothalamus: Approx. 30% are heat sensitive (that is, they fire faster when local heat rises), over 60% are unresponsive to temperature changes and less than 5% are cold sensitive. It was assumed that the temperature setpoint was created by comparing the neuron activity of the temperature-insensitive neurons with the heat-sensitive neurons. In particular, the activity of the cold-sensitive neurons is strongly dependent on excitatory and inhibitory input from neighboring neurons, while the heat-sensitive neurons mainly receive input from the periphery.
Actuators in homoiotherms
For the rule-theoretical technical terms, see system # temperature regulation .
Against hypothermia
In addition to the air temperature, hypothermia and, in extreme cases, frostbite are mainly caused by factors such as precipitation (effect of moisture) and wind (see wind chill ).
Blood circulation
A change in blood flow to the skin does not require any significant expenditure of energy for the body. The vasomotor system causes a narrowing ( vasoconstriction ) or widening ( vasodilation ) of the blood vessels. The control can be done in different ways. Without involvement of the nervous system , the smooth muscles react to local warming or cooling. The local blood flow is changed by contraction or relaxation of the muscles. If a spinal cord reflex is involved , blood flow reactions can be triggered. This is called nervous. Body-wide reactions are absent here as well as with the local reaction of the smooth muscles. Another possibility is to change the circulation as a result of commands from the hypothalamus . This is in contact with cold and heat receptors in the skin and with blood temperature regulating centers.
Vessel enlargement in hot weather - control by the outside temperature:
- When exposed to heat, kinins , especially bradykinin , are split off from plasma globulins by a protease formed in the sweat glands . An increased kinin concentration means that the muscles of the blood vessels in the skin react less strongly to the vasoconstricting effect of the sympathetic nervous system ; they relax and the blood vessels expand.
- Axon reflex hypothesis : The nerve processes of the skin's heat receptors , which extend into the spinal cord via the spinal nerve , have branches, so-called collaterals , which are directly connected to the muscles of the blood vessels , i.e. without intervening synapses , and cause these muscles to slacken in the heat.
Shivering
As with normal muscle work, shivering also creates heat. When trembling, it is used to produce heat. Poikilotherms such as bees , wasps , bumblebees or moths can also warm themselves up through muscle tremors. However, the net yield is low if the body is poorly insulated: Since the muscles have to be supplied with more blood in order to be able to work, a lot of heat is lost when tremors. The core temperature only rises when the muscles have warmed up, see also afterdrop . For shipwrecked people in the water, do not move as much as possible.
Brown adipose tissue - tremor-free heat production
Brown adipose tissue is found almost exclusively in mammals and only in infants and in species that do not weigh more than 10 kilograms in adulthood, and also in a few bird species (Chickadee titmouse and collar grouse ). The reason for this is not known (status ~ 1990). The brown adipose tissue is not found randomly in the organism, but is limited to certain areas: between the shoulder blades, in the neck region and the thoracic region, near the heart and along the aorta near the kidneys.
There are many differences to white, normal fatty tissue. For example, the fat is not stored as one large drop, but in several small droplets. The cells of the brown adipose tissue contain much more cytoplasm and many more mitochondria . In addition, the cells of the brown adipose tissue are innervated by non-myelinated nerve fibers. In contrast, white fat is addressed by hormones . (In the case of brown fat, the transmitter is norepinephrine, and in the case of white fat , the hormone adrenaline , which comes from the adrenal gland - an interesting relationship between the hormonal and nervous systems). The fat from the brown adipose tissue is burned in the cells. One speaks of chemical thermogenesis . The product - namely heat - is carried away with the blood.
acclimatization
During acclimatization , physiological changes take place when there is a long-term change in the milieu. This happens through an enzymatic reaction, a change in molecular structure, or other factors that affect behavior.
Hibernation and hibernation
To be able to do either, a temperature regulation system is required. Therefore, hibernation and hibernation only occur in homoiotherms - and almost exclusively in mammals. There are still a few species of birds that hibernate. Some bird species show a short-term state, which in many ways resembles hibernation. This condition is called torpor and occurs, for example, in the hummingbirds . He helps them get through the night.
In the case of Poikilotherms, the state in which they are in winter at higher latitudes is called cold or winter rigor . This is due to the falling ambient temperature, which also causes your body temperature and thus your metabolic rate to drop. Some poikilotherms have developed the ability to withstand temperatures below freezing. The meal beetle can survive -17 ° C, for example. Species from tropical areas cannot do this. An alligator dies at temperatures just above 0 ° C.
Hibernation
Contrary to popular belief, bears do not hibernate in winter . Real hibernators can only be found in five orders: insectivores ( hedgehogs ), some rodents (e.g. hamsters , marmots ), primates ( fat- tailed lemurs ), bats ( bats ) and turtles .
During hibernation, the respiratory and heartbeat frequencies drop, the total energy expenditure is reduced and the animal falls into a more rigid state than during sleep. It is not dreaming. We know that hamsters and ground squirrels wake up every now and then to - it might sound strange - to sleep. From a purely physiological perspective, hibernation has nothing to do with normal sleep .
It is still unclear which factors lead to hibernation. A certain percentage of fat may be necessary and / or a decrease in the length of the day, ambient temperature and other things. Chronobiology deals with the phenomenon of timing . A hibernator needs to take measures against freezing. Either he wakes up every now and then and walks around or he keeps his temperature constantly at a value just above freezing point. Either way - body temperature must also be controlled during hibernation. It can therefore be assumed that the setpoint is reduced and that measures are only initiated if the value is not reached.
Hibernation
During hibernation , the metabolism is nowhere near as drastically reduced as during hibernation. In bears, for example, the heart rate drops, but it increases for about 30 minutes each day. In addition, many species give birth to their young during hibernation, which definitely requires a regulated endocrine system. Winter resters move while they rest. Still, hibernation can take a long time. During this time, the animals feed on their white adipose tissue or keep supplies.
Hike
In animal migration , including the migration matters is behavior . But behavior can also be used to regulate temperature. Most animal migrations do not happen because of bad weather, but because of the associated food shortage . For example, in some areas of New South Wales in Australia it is quite cold in winter (there) - several degrees below zero at night. Since native trees and bushes are in bloom at this time, the honeyeater , a species of bird , lingers there until there is no more food and only then moves on.
Hair and fur
A fur is made up of hair and, along with the mammary glands, is a key characteristic of mammals. Hair is the homologous formation of the skin of reptile scales or bird feathers .
For all species that do not live in the tropics, changing hair is generally a temperature-regulating measure: Many animals acquire fur with different heat-insulating properties than the previous one in different seasons. A winter coat usually has longer and more dense hair than a summer coat and can hold a thicker layer of calm air in the cold season than in summer. By straightening the hair with the help of hair muscles, the resting air layer can be enlarged. In addition, the air masses trapped in the hair pulp ensure thermal insulation. Species living in water use the effect that air is a much worse conductor of heat than water. Many species make their hair water-repellent by rubbing it with an oily glandular secretion. Tropical species often change individual hairs in an inconspicuous way.
Against overheating
The peak values of the upper critical temperature are relatively close together in all species, since excessive overheating of the body leads to damage to the central nervous system . On the other hand, large differences can be determined for the lower critical temperature. In humans, the sweat limit is just above 30 ° C. If the ambient temperature continues to rise, the organism can endure this as long as the measures taken against overheating are sufficient. Above a certain temperature this is no longer possible and the overheating limit has been reached. It depends on the humidity and is described quantitatively for humans by the heat index . At 30% relative humidity, a person can endure 50 ° C for hours. If the humidity rises to 70%, the bearable maximum temperature is only 40 ° C.
If the body overheats, heat stroke occurs . The blood vessels are maximally dilated and there is no longer enough blood to fill them.
Evaporation cooling
Sweating is a measure that is almost exclusively available to primates . The disadvantage is that the water loss is enormous. Sweating creates evaporative cooling . Even horses take this opportunity, however, the composition of horse sweat is fundamentally different (more protein) and is primarily used for other purposes.
Other animals also use evaporative cooling. Saliva or nasal secretions ( see, for example, Rete mirabile ). Flying foxes and giant kangaroos salivate over their bodies with their tongues. Flying foxes then fan their wings, which accelerates evaporation. The Asian elephant can use its trunk to pull saliva out of its cheek pouches and distribute it over the body. The African elephant , which does not have this possibility, has big ears for it.
When the dog panting , it is about evaporation of nasal secretions. Air is drawn in through the nose and exhaled through the mouth. This behavior can also be observed in cats, sheep and antelopes. Unlike sweating, panting does not remove salt from the body. However, there is a risk of alkalosis (the pH value of the blood rises because too much carbon dioxide is exhaled). The mucous membrane in the turbinates and the oral cavity is traversed by a dense network of arteries and veins, and its many folds give it a huge surface. In dogs, for example, it is larger than the body surface.
Thermal windows
Thermal windows are areas with only thin fur. The insulation is less good at these points. For example, the dog has thermal windows between the front legs, on the chest and in the lumbar region . Depending on your posture, these windows are open or closed.
Also Robben possess this thermal window. As long as they are in the water, there is hardly any risk of overheating. Then they have to protect themselves against hypothermia. An insulating layer of fat can be found in all homoiothermal species living in water. If you go to the land, as seals do during the rutting season, you have to open your thermal windows. With them this happens through different local skin blood flow.
behavior
Behavior can also help against overheating. For example, animals can seek out shady areas, be active at night or carry a “ parasol ” with them, as the African bristle squirrel ( Xerus inauris ) does, which always has its bushy tail to provide shade.
The tropical silk spiders (genus Nephila ) align themselves with the sun in such a way that only the narrow abdomen is directly irradiated. When the body temperature rises more sharply , they withdraw into the shade of a self-woven sun protection in the middle of their bike net . When the morning is cold in the tropics, the spider aligns itself at a 90-degree angle to the sun, so that it can increase its body temperature by up to 7 K. Many desert animals such as the black beetle burrow in the sand during the day to protect themselves from the sun's rays.
Actuator principles
The countercurrent principle
The countercurrent principle is generally a process for heat or material exchange between two liquids or gases. Here in particular the countercurrent principle is used to save energy. (Compare the countercurrent principle in the kidney .) There are two ways of transporting the blood back into the body. The first path leads through the skin veins lying on the surface, the second through the veins lying deep next to the arteries .
Very little blood flows through the superficial vessels in a cold environment; however, the small volume is sufficient to enable metabolic processes. Most of the blood flows through the deep veins and absorbs heat from the arteries so that it reaches the interior of the body already preheated. So it doesn't have to use as much energy to heat it up to core temperature . At the same time, the arterial blood is cooled down as a result of the temperature gradient and reaches the end of the body largely at outside temperature level. The system works extremely effectively: a seagull that was placed in ice water for two hours on a trial basis only lost 1.5 percent of its metabolic heat production via its feet. In the graphic you can see the artery with warm blood coming from the body on the way to the bird's foot in a cold environment.
In a warm environment, the blood takes its way through the superficial skin veins and gives off additional heat. This principle enables whales and seals to reduce heat loss in cool environments. In them, an artery leading to the periphery is completely surrounded by several veins. For example, it allows them to lie on the ice without melting down. Sled dogs can have very different temperatures in their bodies. Since the paws are cool, hardly any heat is given off through them.
Miracle nets - Retia mirabilia
Miracle nets ( Retia mirabilia ) are a special form of the countercurrent principle that occurs in the context of thermoregulation, especially in cats and cloven-hoofed animals . Here, the counter-current principle is not used, as is usually the case, as a measure against hypothermia, but as a cooling system in the head region. Marsupials , primates , rodents , hare-like and odd-toed ungulates lack such a rete mirabile .
An example: If the donkey hare living in the Mojave Desert is hunted for only 10 minutes on a 41 ° C day, its body temperature rises quickly from 41 to 43 ° C, just below the deadly 44 ° C. The brain, an organ that is particularly sensitive to overheating, is the first to be damaged. If the hare hunter is a dog, its brain stays cool because a dog has a miracle net. In his case, the cervical artery branches out and is embedded in the cavernous sinus - a reservoir for venous blood. In this, the arterial blood cools down before it continues to flow into the brain. The temperature difference can be up to 3 ° C.
The blood in the cavernous sinus is relatively cooler, as it comes from the nasal and mouth area of the animal and has been cooled there by evaporation in the nasal concha, which is well supplied with blood (panting). When resting, there is less hacking and less cooling than when exercising. Species without this blood-cooling mechanism must keep their entire body at a temperature that is conducive to the brain . If the cooling occurs through sweating, this means a large loss of water.
Body size of a homoiotherm
Small animals have relatively large surface areas, so they lose a lot of heat ( surface-to-volume ratio (A / V ratio) ). They have to supply a corresponding amount of energy. For example, a shrew eats its own body weight in the form of insects and worms every day . She has to be in search of food almost constantly to cope with this. Hummingbirds can only forage during the day. In order to survive the night, they have to lapse into a torpor in which they drastically lower their body temperature. The size of homoiotherms downwards are therefore limited.
A sphere has the smallest surface of all geometric bodies with the same volume. When comparing the straight line with the mouse-elephant line , the minimum body mass is 1.12 grams. However, this value applies to a perfectly round body. The pig- nosed bat as the smallest mammal and the bee elf (often referred to as the bumblebee hummingbird) as the smallest bird deviate only slightly from the ideal value with 1.5 grams and 1.6 grams respectively.
Poikilothermic animals
In most poikilothermic animals, the heat output in relation to the heat production is so great that they practically assume the temperature of the environment. This applies in particular to animals living in water: Since water contains less than one percent by volume of oxygen ( air : 21 percent by volume), the aquatic animals have to allow a very large amount of the surrounding medium per unit of time to flow over their respiratory exchange surfaces ( gills , skin) to meet their oxygen requirements cover from the water. As a result, the respiratory surfaces also act as heat exchangers with the environment and dissipate up to 60% of the body's heat generated by metabolic activity.
In the case of poikilothermal land animals, it could be demonstrated that the operating temperature differs depending on the species. Their muscle ATPase shows higher or lower activity optima depending on the habitat of the animals. If the animals (for example different species of desert lizards) are offered a temperature gradient in the laboratory , they will look for their preferred temperature for a specific species. In poikilothermal animals, one can often speak of behavior-controlled thermoregulation .
In insects , the intensive metabolism in the flight muscles during flight leads to a build-up of heat, which in large insects cannot be dissipated quickly enough. The chest temperature can rise to 45 ° C during the flight. The operating temperature for many of these larger insects ( butterflies , hymenoptera , grasshoppers , beetles ) is relatively high (25–40 ° C). Therefore they cannot start until this temperature is reached. They have to interrupt their flight if the species-specific temperature range is exceeded or not reached. During the resting phase, their body temperature usually corresponds to that of the surroundings.
But this means that you have to warm up your muscles before the flight starts. This happens through certain behaviors. Either they take a favorable position in relation to the sun and warm themselves up by absorbing heat rays or they generate their own operating temperature by muscle tremors, if this option is available to them. A number of large insects can generate heat through their antagonistic flight muscles, which they activate synchronously. For example the cockchafer on the left . One then speaks of physiological thermoregulation .
Here approaches to an autonomous regulation of body temperature become clear.
In addition to behavior, reptiles also show approaches to autonomous heat regulation. For example, they can increase respiratory evaporation through heat hacking or influence the exchange of heat with the environment by changing the blood circulation in the skin.
Poikilotherme in cold surroundings
As long as most marine invertebrates exist underwater, they stay above the freezing point of their body fluids. However, some can survive sub-zero temperatures. Usually, the formation of ice crystals in cells is fatal because as they grow they tear and destroy tissues. Some animals (e.g. beetles) have substances in their extracellular fluid that accelerate crystal formation. Therefore, this fluid, which washes around the cells from the outside, freezes faster. Freezing causes the fluid to decrease and become more concentrated, which in turn draws water out of the cells and lowers the intracellular freezing point. If the temperature drops further, this process also continues. Since ice crystals cannot cause any damage in the extracellular fluid, a freshwater larva of the Chironomus mosquito, for example, can survive multiple freezes at −32 ° C. Even so, their cells still contain free water. The animal is not known to survive the total freezing of the cell water.
Some animals can become supercool , which means that liquids can be cooled below freezing and still not freeze. For example, glycoproteins serve as antifreeze agents . Although this glycoprotein has been isolated and its chemical structure has been elucidated, the mechanism by which crystal formation is delayed is not known (as of 1990).
Social thermoregulation
Poikilothermic animals ensure a constant nest temperature, for which an isolated nest is necessary.
- The red wood ant uses the sun as a heat source. Specialized heat exchangers heat your body in the sun. In the cooler breeding chambers, they release the stored heat again. If the nest becomes too hot due to the sun's rays, corridors on the shady side are opened so that a cooling draft is created.
- The termite Macrocystis bellicosus maintains colonies of fungi, which it grows on a food pulp. This is fermented by bacteria , which releases heat.
- In colonizing bees , wasps , bumblebees and hornets , heat is produced by the metabolism of the individuals, see also Western honeybee # Thermoregulation of the honeybee
- A bumblebee queen can keep her brood warm on cool days and nights with constant muscle tremors.
- Termites in hot regions achieve a uniform climate in the hive through a complicated hive structure (for example, orientation in north-south direction with compass termites and / or use of chimney effects in the hive).
Further examples of thermoregulation in animals
Thermometer chicken
The thermometer chicken ( Leipoa ocellata ) belongs to the large foot fowl ( Megapodiidae) and lives in dry bush areas in southern Australia . These animals hatch their eggs in a special way. They pile up large piles of leaves and other compostable material in piles up to 150 cm high and lay their eggs in them. By sticking their long beak into the rotting and thus heat-generating mass, they check the temperature inside and, as required, remove leaves or add new ones. This work is done by the males. They keep the temperature at 33 ° C.
Swordfish
The swordfish Xiphias gladius has a retina that is up to 15 ° C warmer than its surroundings during the hunt . The warming to 19 to 28 ° C is done by a muscle behind the eye. This allows the retinal nerve cells to work faster, and the swordfish can locate its prey seven times faster than the prey its predator.
literature
- H. Precht, J. Christophersen, H. Hensel: Temperature and life . Springer Verlag, 1955.
Web links
- Wiener Zeitung : Diagnosis through body heat (regulation thermography) ( Memento from November 1, 2005 in the Internet Archive )
- Archive link: http://www.staff.uni-marburg.de/~sommerh/WS0607-Thermoregulation.pdf ( Memento from June 11, 2007 in the Internet Archive ) HM Sommer: Thermoregulation
Individual evidence
- ↑ Nicole M. Wiesenböck et al .: Taking the heat: thermoregulation in Asian elephants under different climatic conditions. In: J. Comp. Physiol. B 182 (2012), pp. 311-319. doi : 10.1007 / s00360-011-0609-8 .
- ↑ a b c J. A. Boulant: Role of the preoptic-anterior hypothalamus in thermoregulation and fever. In: Clin Infect Dis 31, 2000, pp. 157-161, PMID 11113018 .
- ↑ Why don't birds' feet freeze to death in winter? Spektrum.de September 21, 2007
- ↑ Hans Joachim Schlichting; Bernd Rodewald: About large and small animals. Praxis der Naturwissenschaften- Physik 37/5, 2 (1988)