|
'''Терморегуляция''' — это способность [[животное|животных]] [[организм]]ов поддерживать [[температура|температуру]] тела в определённых границах, даже если температура внешней среды сильно отличается. Этот процесс представляет собой один из аспектов [[гомеостаз]]а — динамически изменяющегося состояния равновесия между внутренней средой организма животного и его внешним окружением. Раздел науки, изучающий такие процессы в [[зоология|зоологии]], называется экофизиологией или физиологической экологией. Если организм не может поддерживать температуру в нормальных для данного вида организмов границах, и температура повышается значительно выше верхней границы нормы, такое состояние называется [[гипертермия|гипертермией]]. Если же температура снижается значительно ниже нижней границы нормы, такое состояние называется [[гипотермия|гипотермией]].
== См. также ==
* [[Акклиматизация]]
* [[Золотой мальчик (ум. 1496)|Золотой мальчик]]
{{zoology-stub}}
{{translate|en|hidden=1}}
<!--
Whereas an organism that ''thermoregulates'' is one that keeps its core body temperature within certain limits, a '''thermoconformer''' changes its body temperature with changes to the temperature outside of its body.
It was not until the introduction of [[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 determine the temperature of those parts which most nearly approaches to that of the [[internal organ]]s. Also for such results to be comparable they must be made in the same situation. The [[rectum]] gives most accurately the temperature of internal parts, or in some cases of sex or species, the [[vagina]], [[uterus]] or [[Urinary bladder|bladder]].
Occasionally the temperature of the [[urine]] as it leaves the [[urethra]] may be of use. More usually the temperature is taken in the [[mouth]], [[underarm|axilla]] or [[groin]].
== Thermoregulation in humans ==
The human thermoregulation is an important aspect of [[human homeostasis]]. 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. In order to deal with these climatic conditions, humans have developed physiologic and cultural modes of adaptation.
The skin assists in homeostasis (keeping different aspects of the body constant e.g. temperature). It does this by reacting differently to hot and cold conditions so that the inner body temperature remains more or less constant. Vasodilation and sweating are the primary modes by which humans attempt to lose excess body heat. The effectiveness of these methods is influenced by the character of the climate and the degree to which the individual is acclimatized.
=== In hot conditions ===
# Sweat glands under the skin secrete [[sweat]] (a fluid containing mostly water with some dissolved ions) which travels up the sweat duct, through the sweat pore and onto the surface of the skin. This causes heat loss by evaporation; however, a lot of essential water is lost.
# The hairs on the skin lie flat, preventing heat from being trapped by the layer of still air between the hairs. This is caused by tiny muscles under the surface of the skin called arrector pili muscles relaxing so that its attached hair follicle is not erect. These flat hairs increase the flow of air next to the skin increasing heat loss by convection and conduction.
# [[Arterioles]] carrying blood to the superficial capillaries under the surface of the skin can swell (dilate) so that more heat is carried by the blood and is lost to the air increases heat loss by radiation and conduction. This is called vasodilation.
=== In cold conditions ===
# Sweat stops being produced.
# The minute muscles under the surface of the skin called erector muscles (attached to an individual hair follicle) contract ([[piloerection]]), lifting the hair follicle upright. This makes our hairs stand on end which acts as an insulating layer, trapping heat. This is what also causes goose pimples since humans don’t have very much hair and the contracted muscles can easily be seen.
# [[Arterioles]] carrying blood to superficial capillaries under the surface of the skin can shrink (constrict) so that less heat is carried by the blood and lost to the surroundings. This process is called vasoconstriction. It is impossible to prevent all heat loss from the blood, only to reduce it. In extremely cold conditions excessive vasoconstriction leads to numbness and [[frostbite]].
# Muscles can also receive messages from the thermo-regulatory centre of the brain (the [[hypothalamus]]) to cause shivering. This increases heat production as respiration is an exothermic reaction in muscle cells that accelerates when they contract.
''Note'': Messages from the brain that reach effectors (e.g. muscles and glands) are done so by motor neurons. Neurons are specialized cells that pass messages around the body in the form of electrical impulses. Motor neurons are the ones that pass messages from the brain directly to the effector, in this case muscles. A collection of thousands of neurons is termed a nerve.
The process explained above, in which the skin regulates body temperature, is called thermoregulation. This is also called homeostasis or is a part of homeostasis since it is keeping conditions in the body relatively constant.
== Temperature symptoms ==
[[Temperature symptoms]] and medications:
* [[Hypothermia]]
* [[Hyperthermia]]
* [[Raynaud's phenomenon]] ([[Raynaud's disease]])
* [[Induced hypothermia]]
* [[Cold hands (medical symptom)]]
* [[Temperature sensitivity]]
== Thermoregulation in vertebrates ==
[[Image:thermoregulation simplified.png|thumb|250px|Human thermoregulation (simplified)]]
By numerous observations upon [[homo sapiens sapiens|humans]] 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. This is called '''[[Homeothermic|homeothermy]]'''. Almost all other animals display a variation of body temperature, dependent on their surroundings. This is called '''[[Poikilothermic|poikilothermy]]'''.
Certain mammals are exceptions to this rule, being warm-blooded during the summer or daytime, but cold-blooded during the winter when they [[hibernation|hibernate]] or at night during sleep. [[J. O. Wakelin Barratt]] has demonstrated that under certain pathological conditions, a warm-blooded (homeothermic) animal may become temporarily cold-blooded (poikilothermic). He has shown conclusively that this condition exists in rabbits suffering from rabies during the last period of their life, the rectal temperature being then within a few degrees of the room temperature and varying with it. He explains this condition by the assumption that the nervous mechanism of heat regulation has become paralysed. The respiration and heart-rate being also retarded during this period, the resemblance to the condition of hibernation is considerable. Again, [[Sutherland Simpson]] has shown that during deep anaesthesia a warm-blooded animal tends to take the same temperature as that of its environment. He demonstrated that when a monkey is kept deeply anaesthetized with ether and is placed in a cold chamber, its temperature gradually falls, and that when it has reached a sufficiently low point (about 25 °C in the monkey), the employment of an anaesthetic is no longer necessary, the animal then being insensible to pain and incapable of being roused by any form of stimulus; it is, in fact, narcotised by cold, and is in a state of what may be called «artificial [[hibernation]].» Once again this is explained by the fact that the heat-regulating mechanism has been interfered with. Similar results have been obtained from experiments on cats.
=== Ectotherms ===
: ''Main article: [[Ectotherm]]''
==== Ectothermic cooling ====
[[Image:BFAL SOTE shade.JPG|thumb|320px|Seeking shade is one method of cooling. Here [[Sooty Tern]] chicks are using a [[Black-footed Albatross]] chick for shade.]]
* Vaporization:
** Getting wet in a river, lake or sea.
* Convection:
** Climbing to lower ground from trees, into valleys, [[burrow]]s, etc.
** Entering a cold water or air current.
** Building a nest that allows natural or generated air/water flow for cooling.
* Conduction:
** Lie on cold ground.
** Staying wet in a river, lake or sea.
** Covering in cool mud.
* Radiation:
** Find shade.
** Enter a burrow shaped for radiating heat (Black box effect).
** Expand folds of skin.
** Expose wing surfaces.
==== Ectothermic heating (or minimising heat loss) ====
* Convection:
** Climb to higher ground up trees, ridges, rocks.
** Entering a warm water/air current.
** Building an insulated nest or burrow.
* Conduction:
** Lie on hot rock.
* Radiation:
** Lie in sun.
** Fold skin to reduce exposure.
** Conceal wing surfaces.
[[Image:wiki stranglesnake.jpg|thumb|Thermographic image of a snake around an arm]]
To cope with low temperatures, some [[fish]] have developed the ability to remain functional even when the water temperature is below freezing; some use natural [[antifreeze]] or [[antifreeze proteins]] to resist ice crystal formation in their tissues. [[Amphibian]]s and [[reptile]]s cope with heat loss by evaporative cooling and behavioral adaptations.
=== Endotherms ===
: ''Main article: [[Endotherm]]''
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, 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. [[Bird]]s also avoid overheating by panting since their thin skin has no sweat glands. [[Down feathers]] 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 like whales this is referred to as blubber. Dense coats found in desert endotherms also aid in preventing heat gain. Another cold weather strategy is to temporarily decrease metabolic rate and body temperature regulated decrease in body temperature decreases the temperature difference between the animal and the air and therefore minimizes heat loss. Furthermore, having a lower metabolic rate is less energetically expensive. Many animals survive cold frosty nights through [[torpor]], a short-term temporary drop in body temperature. Organisms when presented with the problem of regulating body temperature not only have 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 now adjusted temperature to the Stimulus. This cyclical process aids in homeostasis.
==== Heat production in birds and mammals ====
In cold environments, birds and mammals employ the following adaptations and strategies to minimize heat loss:
# using small smooth muscles (erector pili in mammals) which are attached to feather or hair shafts; this shivering thermogenesis distorts the surface of the skin as the feather/hair shaft is made more erect (called [[goose bumps]] or pimples)
# 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 [[Bergmann's Rule]]))
# having the ability to store energy as fat for [[metabolism]]
# have shortened extremities
# have [[countercurrent exchange|countercurrent blood flow]] in extremities (e.g. [[Arctic Wolf]]<ref>{{cite journal
| last = Swan
| first = K. G.
| authorlink =
| coauthors = R. E. Henshaw
| title = Lumbar sympathectomy and cold acclimatization by the arctic wolf.
| journal = Analysis of Surgery
| volume = 177
| issue =
| pages = 286-292
| publisher =
| date = March, 1973
| url = http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1355529&pageindex=1
| doi =
| id =
| accessdate = 03/29/2007 }}</ref> or penguins<ref>[http://www.seaworld.org/infobooks/Penguins/adaptations.html Adaptations for an Aquatic Environment]. SeaWorld/Busch Gardens Animal Information Database, 2002. Last accessed November 27, 2006.</ref><ref>[http://www.penguins.cl/penguins-intro.htm Introduction to Penguins]. Mike Bingham, International Penguin Conservation Work Group. Last accessed November 27, 2006.</ref>) to avoid freezing of tissues
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
== Thermoregulation in plants ==
[[Thermogenesis]] occurs in the flowers of many plants in the [[Araceae]] family as well as in [[cycad]] cones.<ref name=Minorsky>{{Citation |url=http://www.plantphysiol.org/cgi/content/full/132/1/25 |title=The Hot and the Classic |journal=Plant Physiol |date=May 2003 |volume=132 |pages=25-26 |first=Peter V. |last=Minorsky}}</ref> In addition, some plants in the [[Alum]] family — such as the [[Eastern Skunk Cabbage]], the [[Philodendron]] (''Philodendron selloum''), and the [[Sacred lotus]] (''Nelumbo nucifera'') are able to thermoregulate themselves,<ref>{{Citation |url=http://www.google.com/url?sa=t&ct=res&cd=1&url=http%3A%2F%2Fwww.me.berkeley.edu%2FME212%2Flec6%2Fi_Plants_Thermoregulation.pdf&ei=gVVUR4z0G5augwOeqcykDA&usg=AFQjCNEjjhXzZlJvy_6twTc2TBJEgK4z9g&sig2=kaMDy1_DobkrDUdK6pXfZw
|title=Plants Thermoregulation |accessdate=12/3/2007 }}</ref> remaining on average 20 °C (36 °F) above air temperature while flowering. Heat is produced by breaking down the starch that was stored in their roots,<ref>{{Citation |url=http://www.natureinstitute.org/pub/ic/ic4/skunkcabbage.htm |title=Skunk Cabbage (Symplocarpus foetidus) |journal=The Nature Institute |year=2000 |pages=12-18 |first=Craig |last=Holdrege }}</ref> which requires the consumption of oxygen at a rate approaching that of a flying [[hummingbird]].<ref>{{Citation |url=http://www.sciencemag.org/cgi/content/abstract/178/4066/1195?ijkey=dd3819980cc11bd54b2042f16aa2a938c57230b5&keytype2=tf_ipsecsha |title=Temperature Regulation by the Inflorescence of Philodendron | authors=Kenneth A. Nagy, Daniel K. Odell, and Roger S. Seymour |journal=Science |date=Dec 1972 |volume=178 |pages=1195-1197 }}</ref>
One possible explanation for plant thermoregulation is to provide protection against cold temperature. For example, the skunk cabbage is not frost-resistance, yet it begins to grow and flower when there is still snow on the ground.<ref name=Minorsky /> 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.<ref>{{Citation |title=Thermogenesis in three Philodendron species (Araceae) of French Guiana |first=Marc |last=Gibernau |first2=Denis |last2=Barabé |year=2000 |journal=Canadian Journal of Botany |url=http://www.google.com/url?sa=t&ct=res&cd=1&url=http%3A%2F%2Fwww.edb.ups-tlse.fr%2Fequipe3%2FMG%2Fpublis%2Fthermo.pdf&ei=D15UR8awDJKGhAO0wcykDA&usg=AFQjCNHp6sQ3CRZUBVLP7i2EHXCw4SNbCQ&sig2=lO43VJmbwkRTVVhVJFe5TA }}</ref>
== Behavioural temperature regulation ==
In addition to human beings, a number of other animals also maintain their body temperature with physiological and behavioral adjustments. For example, a desert lizard is an [[ectotherm]] and is therefore unable to control its temperature through metabolic regulation. However, by altering its location continuously, it is able to maintain a crude form of temperature control. In the morning, only its head will emerge from its burrow. Later, the entire body is exposed. The lizard basks in the sun, absorbing solar heat. When the temperature reaches higher levels, the lizard will hide under rocks or return to its burrow. When the sun goes down or the temperature falls, it emerges again.
Some animals living in cold environments maintain their body temperature by preventing heat loss. Their fur grows more densely to increase the amount of [[Thermal insulation|insulation]]. Some animals are [[heterothermic|regionally heterothermic]] and are able to allow their less insulated extremities to cool to temperatures much lower than their core temperature — nearly to 0 °C. This minimizes heat loss through less insulated body parts, like the legs, feet (or hooves), and nose.
[[Image:wiki ostrich.jpg|thumb|An ostrich can keep its body temperature very constant, even though it can be very hot during the day and cold at night.]]
=== Hibernation, estivation, and daily torpor ===
To cope with limited food resources and low temperatures, some mammals [[hibernation|hibernate]] in underground burrows. In order to remain in «stasis» for long periods, these animals must build up [[Brown adipose tissue|brown fat]] reserves and be capable of slowing all body functions. True hibernators (e.g. groundhogs) keep their body temperature down throughout their hibernation while the [[core temperature]] of false hibernators (e.g. bears) varies with them sometimes emerging from their dens for brief periods. Some bats are true hibernators which rely upon a rapid, non-shivering thermogenesis of their brown fat deposit to bring them out of hibernation.
[[Estivation]] occurs in summer (like [[siesta]]s) and allows some mammals to survive periods of high temperature and little water (e.g. turtles burrow in pond mud).
Daily [[torpor]] occurs in small endotherms like bats and humming birds which temporarily reduce their high metabolic rates to conserve energy.<ref>{{Citation |title=Biology: Concepts and Applications |first=Cecie |last=Starr |year=2005 |publisher=Thomson Brooks/Cole |pages=639 | isbn=053446226X |url=http://books.google.com/books?id=RtSpGV_Pl_0C&pg=PA639&dq=cold+temperatures+birds+minimize+heat+loss&ei=K89ZR4HhKImssgOGwsHRCw&sig=npWc-dz0QUTa-pkxj7bOgpjKq8M
}}</ref>
== Variations in the temperature of human beings and some animals ==
[[Image:1911 Animal heat.png|thumb|Chart showing diurnal variation in body temperature, ranging from about 37.5 °C from 10 a.m. to 6 p.m., and falling to about 36.3 °C from 2 a.m. to 6 a.m.]]
=== Normal human temperature ===
{{main|Normal human body temperature}}
Previously, average oral temperature for healthy adults had been considered 37.0 °C (98.6 °F), while normal ranges are 36.1 °C (97.0 °F) to 37.8 °C (100.0 °F). In Russia, the temperature had been measured axillary. 36.6 °C was considered «ideal» temperature, while normal ranges are 36 °C to 36.9 °C.
Recent studies suggest that the average temperature for healthy adults is 98.2 °F or 36.8 °C (same result in three different studies). Variations (one [[standard deviation]]) from three other studies are:
* 36.4 — 37.1 °C
* 36.3 — 37.1 °C for males, 36.5 — 37.3 °C for females
* 36.6 — 37.3 °C<ref name=factbook>{{Citation |title=Temperature of a Healthy Human (Body Temperature) |work=The Physics Factbook |last=Wong |first=Lena |url=http://hypertextbook.com/facts/LenaWong.shtml |year=2005 }}</ref>
=== Variations from thermometer placement ===
Temperature varies according to thermometer placement, with rectal temperature being 0.3-0.6 °C (0.5-1 °F) higher than oral temperature, while axillary temperature is 0.3-0.6 °C (0.5-1 °F) lower than oral temperature.<ref>{{Citation |url=http://health.yahoo.com/topic/hearing/resources/article/healthwise/tw9223 |title=Rectal, ear, oral, and axillary temperature comparison |publisher=Yahoo Health }}</ref> The average difference between oral and axillary temperatures of [[India]]n children aged 6-12 was found to be only 0.1 °C (standard deviation 0.2 °C),<ref>{{Citation |url=http://www.indianpediatrics.net/june2004/600.pdf |title=Comparison of Axillary Temperature with Rectal or Oral Temperature and Determination of Optimum Placement Time in Children |authors=Deepti Chaturvedi, K.Y. Vilhekar, Pushpa Chaturvedi, M.S. Bharambe |journal=INDIAN PEDIATRICS |volume=41 |year=2003 |date=June 17, 2004 |pages=600-603 }}</ref> and the mean difference in [[Malta]] 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.<ref>{{Citation |url=http://www.annemergmed.com/article/PIIS0196064404002318/fulltext |title=How reliable is axillary temperature measurement? |first=E.C. |last=Quintana |volume=43 |issue=6 |pages=797-798 |date=June 2004 |doi=10.1016/j.annemergmed.2004.03.010 |journal=Annuals of Emergency Medicine }}</ref>
=== Variations associated with development ===
Of the lower warm-blooded animals, there are some that appear to be cold-blooded at birth. [[cat|Kittens]], [[rabbit]]s and [[dog|puppies]], if removed from their surroundings shortly after birth, lose their body heat until their temperature has fallen to within a few degrees of that of the surrounding air. But such animals are at birth blind, helpless and in some cases naked. Animals who are born when in a condition of greater development can maintain their temperature fairly constant. In strong, healthy infants a day or two old the temperature rises slightly, but in that of weakly, ill-developed children it either remains stationary or falls. The cause of the variable temperature in infants and young immature animals is the imperfect development of the nervous regulating mechanism.
The average temperature falls slightly from [[Infant|infancy]] to [[puberty]] and again from puberty to [[middle age]], but after that stage is passed the temperature begins to rise again, and by about the [[Old age|eightieth year]] is as high as in infancy.
=== 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]]s also have a well-marked and regular diurnal variation of body temperature which follows periods of rest and activity, and is not dependent on the incidence of day and night; [[nocturnal]] 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 temperature can be reversed by reversing their daily routine.<ref name=Simpson>{{Citation |first=Sutherland |last=Simpson |first2=J.J. |last2=Galbraith |year=1905 |title=An investigation into the diurnal variation of the body temperature of nocturnal and other birds, and a few mammals |journal=The Journal of Physiology Online |url=http://jp.physoc.org/cgi/reprint/33/3/225.pdf }}</ref>
The temperature curve of [[Diurnal animal|diurnal]] birds is essentially similar to that of man and other homoeothermal animals, except that the maximum occurs earlier in the afternoon and the minimum earlier in the morning. Also that the curves obtained from rabbits, [[guinea pig]]s and dogs were quite similar to those from man. These observations indicate that body temperature is partially regulated by [[circadian rhythm]]s.
=== Variations due to women’s menstrual cycles ===
During the [[follicular phase]] (which lasts from the first day of [[menstruation]] until the day of [[ovulation]]), the average [[basal body temperature]] in women ranges from 36.45 — 36.7 °C (97.6 — 98.6 °F). Within 24 hours of ovulation, women experience an elevation of 0.15 — 0.45 °C (0.2 — 0.9 °F) due to the increased metabolic rate caused by sharply elevated levels of [[progesterone]]. The basal body temperature ranges between 36.7 — 37.3 °C (97.6 — 99.2 °F) throughout the [[luteal phase]], and drops down to pre-ovulatory levels within a few days of menstruation.<ref>{{Citation |url=http://books.google.com/books?id=JZb0ibgYDCIC&pg=PA149&lpg=PA149&dq=temperature+higher+during+follicular+phase&source=web&ots=p3YUztWz7m&sig=wUfFvX5X-IQTkRHt7reLTW-Y73E |title=Women's Sports Medicine and Rehabilitation |isbn=0834217317 |publisher=Lippincott Williams & Wilkins |year=2001 |last= Swedan |first=Nadya Gabriele |pages=149 }}</ref> Women can chart this phenomenon to determine whether and when they are ovulating, or to aid conception or contraception.
=== Variations due to fever ===
[[Fever]] is a regulated elevation of the set point of core temperature in the [[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 that people without fever do not.
=== Variations due to biofeedback ===
A group of monks known as the [[Tummo]] are known to practice [[biofeedback]] [[meditation]] techniques that allow them to raise their body temperatures substantially.<ref name=harvardgazette>{{Citation |url=http://www.hno.harvard.edu/gazette/2002/04.18/09-tummo.html |title=Meditation changes temperatures: Mind controls body in extreme experiments |first=William J. |last=Cromie |publisher=Harvard Gazette |year=2002 }}</ref>
=== Variations due to other factors ===
{{disputed-section}}
In Simpson’s & Galbraith’s work, the mean temperature of the female was higher than that of the male in all the species examined whose sex had been determined.
Meals sometimes cause a slight elevation, sometimes a slight depression—alcohol seems always to produce a fall. Exercise and variations of external temperature within ordinary limits cause very slight change, as there are many compensating influences at work, which are discussed later. The core temperature of those living in the tropics is within a similar range to those dwelling in the [[Arctic]] regions.
== Low body temperature increases lifespan ==
It was long theorised that low body temperature may prolong life. On November 2006, a team of scientists from the [[Scripps Research Institute]] reported that transgenic mice which had body temperature 0.3-0.5 C lower than normal mice (due to overexpressing the uncoupling protein 2 in hypocretin neurons (Hcrt-UCP2), which elevated hypothalamic temperature, thus forcing the [[hypothalamus]] to lower body temperature) indeed lived longer than normal mice. The lifespan was 12 % longer for males and 20 % longer for females. Mice were allowed to eat as much as they wanted. <ref name=sciencemag>[http://www.sciencemag.org/cgi/content/abstract/314/5800/825 Transgenic Mice with a Reduced Core Body Temperature Have an Increased Life Span], by Bruno Conti et al. Science, 3, November 2006</ref> <ref name=sciencedaily>[http://www.sciencedaily.com/releases/2006/11/061103083756.htm Reduced Body Temperature Extends Lifespan, Study Finds]</ref> <ref>[http://balancinglife.blogspot.com/2006/11/be-cool-live-long.html Bee cool, live long]</ref> The effects of body temperature on longevity have not been studied in humans.
== Limits compatible with life ==
There are limits both of heat and cold that a warm-blooded animal can bear, and other far wider limits that a cold-blooded animal may endure and yet live. The effect of too extreme a cold is to lessen metabolism, and hence to lessen the production of heat. Both catabolic and [[Anabolism|anabolic]] changes share in the depression, and though less energy is used up, still less energy is generated. This diminished [[metabolism]] tells first on the [[central nervous system]], especially the [[brain]] and those parts concerned in consciousness. Both [[heart rate]] and [[respiration rate]] become diminished, drowsiness supervenes, becoming steadily deeper until it passes into the sleep of death. Occasionally, however, [[convulsion]]s may set in towards the end, and a death somewhat similar to that of [[asphyxia]] takes place.
In some experiments on cats performed by Sutherland Simpson and Percy T. Herring, they found them unable to survive when the rectal temperature was reduced below 16 °C. At this low temperature respiration became increasingly feeble, the heart-impulse usually continued after respiration had ceased, the beats becoming very irregular, apparently ceasing, then beginning again. Death appeared to be mainly due to asphyxia, and the only certain sign that it had taken place was the loss of knee jerks.
On the other hand, too high a temperature hurries on the metabolism of the various tissues at such a rate that their capital is soon exhausted. Blood that is too warm produces [[dyspnea]] and soon exhausts the metabolic capital of the respiratory centre. Heart rate is increased, the beats then become arrhythmic and finally cease. The central nervous system is also profoundly affected, consciousness may be lost, and the patient falls into a [[comatose]] condition, or [[delirium]] and convulsions may set in. All these changes can be watched in any patient suffering from an acute [[fever]]. The lower limit of temperature that man can endure depends on many things, but no one can survive a temperature of 45 °C (113 °F) or above for very long. [[Mammal]]ian muscle becomes rigid with heat rigor at about 50 °C, and obviously should this temperature be reached the sudden rigidity of the whole body would render life impossible.
H.M. Vernon has done work on the death temperature and paralysis temperature (temperature of heat rigor) of various animals. He found that animals of the same class of the animal kingdom showed very similar temperature values, those from the [[Amphibia]] examined being 38.5 °C, [[Fish]] 39 °C, [[Reptilia]] 45 °C, and various [[Mollusc]]s 46 °C. Also in the case of [[Pelagic]] animals he showed a relation between death temperature and the quantity of solid constituents of the body, Cestus{{Fact|date=February 2007}} having lowest death temperature and least amount of solids in its body. In higher animals, however, his experiments tend to show that there is greater variation in both the chemical and physical characters of the [[protoplasm]], and hence greater variation in the extreme temperature compatible with life.
== Human temperature variation effects ==
=== Hot ===
Fevers are not to be confused with heat stroke. In fever the person can feel cold at high body temperatures since the body is fooled into thinking it is cold because the body thermostat is set higher than usual.
* '''37 °C (98.6 °F)''' — Normal body temperature (which varies between about 36.12-37.5°C (96.8-99.5°F)
* '''38 °C (100.4 °F)''' — Sweating, feeling very uncomfortable, slightly hungry.
* '''39 °C (102.2 °F)''' — Severe sweating, flushed and very red. Fast heart rate and breathlessness. There may be exhaustion accompanying this. Children and people with epilepsy may be very likely to get convulsions at this point.
* '''40 °C (104 °F)''' — Fainting, dehydration, weakness, vomiting, headache and dizziness may occur as well as profuse sweating.
* '''41 °C (105.8 °F)''' — ([[Medical emergency]]) — Fainting, vomiting, severe headache, dizziness, confusion, hallucinations, delirium and drowsiness can occur. There may also be palpitations and breathlessness.
* '''42 °C (107.6 °F)''' — Subject may turn pale or remain flushed and red. They may become comatose, be in severe delirium, vomiting, and convulsions can occur. Blood pressure may be high or low and heart rate will be very fast.
* '''43 °C (109.4 °F)''' — Normally death, or there may be serious brain damage, continuous convulsions and shock. Cardio-respiratory collapse will occur.
* '''44 °C (111.2 °F) or more''' — Almost certainly death will occur; however, patients have been known to survive up to 46.5 °C (115.7 °F).<ref name="Body Temp Records">{{Citation |url=http://www.powells.com/biblio?show=0553587129&page=excerpt |title=Excerpt: Humans, Body Extremes |publisher=Guinness World Records |year=2004 |accessdate=November 27, 2006 }}</ref>
=== Cold ===
* '''37 °C (98.6 °F)''' — Normal body temperature (which varies between about 36-37.5°C (96.8-99.5°F)
* '''36 °C (96.8 °F)''' — Mild to moderate shivering (it drops this low during sleep). May be a normal body temperature.
* '''35 °C (95.0 °F)''' — ([[Hypothermia]]) is less than 35 °C (95.0 °F) — Intense shivering, numbness and bluish/grayness of the skin. There is the possibility of heart irritability.
* '''34 °C (93.2 °F)''' — Severe shivering, loss of movement of fingers, blueness and confusion. Some behavioural changes may take place.
* '''33 °C (91.4 °F)''' — Moderate to severe confusion, sleepiness, depressed reflexes, progressive loss of shivering, slow heart beat, shallow breathing. Shivering may stop. Subject may be unresponsive to certain stimuli.
* '''32 °C (89.6 °F)''' — ([[Medical emergency]]) Hallucinations, delirium, complete confusion, extreme sleepiness that is progressively becoming comatose. Shivering is absent (subject may even think they are hot). Reflex may be absent or very slight.
* '''31 °C (87.8 °F)''' — Comatose, very rarely conscious. No or slight reflexes. Very shallow breathing and slow heart rate. Possibility of serious heart rhythm problems.
* '''28 °C (82.4 °F)''' — Severe heart rhythm disturbances are likely and breathing may stop at any time. Patient may appear to be dead.
* '''24-26°C (75.2-78.8°F) or less''' — Death usually occurs due to irregular heart beat or respiratory arrest; however, some patients have been known to survive with body temperatures as low as 14.2 °C (57.5 °F).<ref name="Body Temp Records"/>
== Notes ==
{{reflist|2}}
== References ==
* ''Handbook of Physiology'', Kirkes, (Philadelphia, 1907)
* Simpson, S. & Galbraith, J.J. (1905) Observations on the normal temperatures of the monkey and its diurnal variation, and on the effects of changes in the daily routine on this variation. Transactions of the Royal Society of Edinburgh 45: 65-104.
* Weldon Owen Pty Ltd. (1993). ''Encyclopedia of animals — Mammals, Birds, Reptiles, Amphibians.'' Reader’s Digest Association, Inc. Pages 567—568. ISBN 1-875137-49-1.
== See also ==
* [[Normal human body temperature]]
* [[Innate heat]]
* [[Wilson's temperature syndrome]]
== External links ==
* {{Cite web
| last = Wong
| first = Lena
| title = Temperature of a Healthy Human (Body Temperature)
| work = The Physics Factbook
| accessdate = 2007-08-22
| year = 1997
| url = http://hypertextbook.com/facts/LenaWong.shtml
}}
* {{MeshName|Thermoregulation}}
{{1911}}
-->
== См. также ==
* [[Акклиматизация]]
* [[Золотой мальчик (ум. 1496)|Золотой мальчик]]
[[Категория:Терморегуляция|*]]
| 