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Thermoregulation
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{{redirect|Body heat||Body Heat (disambiguation)}}{{redirect|Body temperature|information regarding normal human body temperature|Human body temperature|the 2011 Japanese film|Body Temperature (film)}}{{Use dmy dates|date=October 2013}}{{Thermoreg}}Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature as its own body temperature, thus avoiding the need for internal thermoregulation. The internal thermoregulation process is one aspect of homeostasis: a state of dynamic stability in an organism's internal conditions, maintained far from thermal equilibrium with its environment (the study of such processes in zoology has been called physiological ecology). If the body is unable to maintain a normal temperature and it increases significantly above normal, a condition known as hyperthermia occurs. For humans, this occurs when the body is exposed to constant temperatures of approximately {{convert|55|°C|°F}}, and with prolonged exposure (longer than a few hours) at this temperature and up to around {{convert|75|°C|°F}} death is almost inevitable.{{Citation needed|date=June 2011}} Humans may also experience lethal hyperthermia when the wet bulb temperature is sustained above {{convert|35|°C|°F}} for six hours.WEB,weblink Global Warming: Future Temperatures Could Exceed Livable Limits, Researchers Find, The opposite condition, when body temperature decreases below normal levels, is known as hypothermia. 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 {{convert|37|°C|°F}}, and hypothermia sets in when the core body temperature gets lower than {{convert|35|°C|°F}}.NEWS,weblink Hypothermia, Mayo Clinic, 2017-05-01, en, 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.NEWS,weblink Hypothermia: Causes, Symptoms, and Treatment, WebMD, 2017-05-01, en-US, It was not until the introduction of thermometers 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 organs. Also, for such results to be comparable, the measurements must be conducted under comparable conditions. The rectum has traditionally been considered to reflect most accurately the temperature of internal parts, or in some cases of sex or species, the vagina, uterus or bladder.{{sfn|Chisholm|1911|p=48}}Occasionally the temperature of the urine as it leaves the urethra may be of use in measuring body temperature. More often the temperature is taken in the mouth, axilla, ear or groin.{{sfn|Chisholm|1911|p=49}}Some animals undergo one of various forms of dormancy where the thermoregulation process temporarily allows the body temperature to drop, thereby conserving energy. Examples include hibernating bears and torpor in bats.

Classification of animals by thermal characteristics

{{unreferenced section|date=March 2016}}

Endothermy vs. ectothermy

Thermoregulation in organisms runs along a spectrum from endothermy to ectothermy. Endotherms 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.WEB,weblink Khan Academy, Khan Academy, en, 2017-04-03, 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.JOURNAL, Boundless, 2016-09-20, Homeostasis: Thermoregulation,weblink Boundless, en, Ectotherms 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

File:BFAL SOTE shade.JPG|thumb|320px|Seeking shade is one method of cooling. Here sooty tern chicks are using a black-footed albatrossblack-footed albatross

Ectothermic cooling

  • Vaporization:
  • 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.
(File:Lizard Thermoregulation.svg|right|thumb|200px|The red line represents the air temperature.The purple line represents the body temperature of the lizard.The green line represents the base temperature of the burrow.Lizards are ectotherms and use behavioral adaptations to control their temperature. They regulate their behavior based on the temperature outside, if it is warm they will go outside up to a point and return to their burrow as necessary.)
  • 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.
File:wiki stranglesnake.jpg|thumb|ThermographicThermographicTo 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. Amphibians and reptiles cope with heat loss 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, 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. Birds also counteract overheating by gular fluttering, or rapid vibrations of the gular (throat) skin. 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, such as whales, or animals that live in very cold regions, such as the polar bears, this is called blubber. 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, 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 and poikilothermy refer to how stable an organism's deep-body temperature is. Most endothermic organisms are homeothermic, like mammals. However, animals with facultative endothermy are often poikilothermic, meaning their temperature can vary considerably. Most 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 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). Almost all other animals display a variation of body temperature, dependent on their surroundings (poikilothermy).{{sfn|Chisholm|1911|p=49}}

Brain control

Thermoregulation in both ectotherms and endotherms is controlled mainly by the preoptic area of the anterior hypothalamus. Such homeostatic control is separate from the sensation of temperature.JOURNAL, Romanovsky, AA, 2007, Functional architecture of the thermoregulatory system,weblink Am J Physiol Regul Integr Comp Physiol, 292, 1, R37–46, 10.1152/ajpregu.00668.2006, 17008453,

In birds and mammals

File:Kangaroo licking itself to cool.jpg|thumb|250px|Kangaroo lickinglickingIn cold environments, birds and mammals employ the following adaptations and strategies to minimize heat loss:
  1. Using small smooth muscles (arrector pili 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 or pimples) which slows the movement of air across the skin and minimizes heat loss.
  2. 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))
  3. Having the ability to store energy as fat for metabolism
  4. Have shortened extremities
  5. Have countercurrent blood flow 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 wolfJOURNAL, Swan, K. G., R. E. Henshaw, Lumbar sympathectomy and cold acclimatization by the arctic wolf, Analysis of Surgery, 177, 3, 286–292, March 1973, 10.1097/00000658-197303000-00008, 4692116, 1355529, or penguinsAdaptations for an Aquatic Environment. SeaWorld/Busch Gardens Animal Information Database, 2002. Last accessed 27 November 2006.Introduction to Penguins. Mike Bingham, International Penguin Conservation Work Group. Last accessed 27 November 2006.)
In warm environments, birds and mammals employ the following adaptations and strategies to maximize heat loss:
  1. Behavioural adaptations like living in burrows during the day and being nocturnal
  2. Evaporative cooling by perspiration and panting
  3. Storing fat reserves in one place (e.g., camel's hump) to avoid its insulating effect
  4. Elongated, often vascularized extremities to conduct body heat to the air

In humans

File:Thermoregulation simplified.png|thumb|right|400px|Simplified control circuit of human thermoregulation.JOURNAL, Kanosue, K., Crawshaw, L. I., Nagashima, K., Yoda, T., 2009, Concepts to utilize in describing thermoregulation and neurophysiological evidence for how the system works, European Journal of Applied Physiology, 109, 1, 5–11, 10.1007/s00421-009-1256-6, 19882166, ]]As in other mammals, thermoregulation is an important aspect of human homeostasis. Most body heat is generated in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles.BOOK, 2006, Guyton, A.C., & Hall, J.E., Textbook of Medical Physiology, 11th, Philadelphia, Elsevier Saunders, 890, 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."Heat Exhaustion: Symptoms and Treatment". WebMD. Retrieved 2017-03-01Harmon, Katherine. "How Does a Heat Wave Affect the Human Body?". Scientific American. Retrieved 2017-03-01 For humans, adaptation to varying climatic conditions includes both physiological mechanisms resulting from 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.”"Thermoregulation". www.unm.edu. Retrieved 2017-03-01. This organ possesses control mechanisms as well as key temperature sensors, which are connected to nerve cells called thermoreceptors.Boundless (2016-05-26). "Thermoreception". Boundless. 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.Tansey, Etain A.; Johnson, Christopher D. (2015-09-01). "Recent advances in thermoregulation". Advances in Physiology Education. 39 (3): 139–148. {{doi|10.1152/advan.00126.2014}}. {{ISSN|1043-4046}}. {{PMID|26330029}}."Temperature Regulation of the Human Body". hyperphysics.phy-astr.gsu.edu. Retrieved 2017-03-01.There are three avenues of heat loss: convection, conduction, and radiation. If skin temperature is greater than that of the surroundings, the body can lose heat by radiation and conduction. But, if the temperature of the surroundings is greater than that of the skin, the body actually gains heat by radiation 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.Wilmore, Jack H., & Costill, David L. (1999). Physiology of sport and exercise (2nd ed). Champaign, Illinois: Human Kinetics. 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(File:Irish Wolfhound mix, panting.ogv|thumb|A dog panting after exercise)

In plants

Thermogenesis occurs in the flowers of many plants in the Araceae family as well as in cycad cones.JOURNAL,weblink The Hot and the Classic, Plant Physiol, May 2003, 132, 25–26, Peter V., Minorsky, 10.1104/pp.900071, 12765187, 1, 1540311, In addition, the sacred lotus (Nelumbo nucifera) is able to thermoregulate itself,BOOK,weblink
deadurl=yes weblink >archivedate=2012-05-07 JOURNAL=THE NATURE INSTITUTE PAGES=12–18 LAST=HOLDREGE, which requires the consumption of oxygen at a rate approaching that of a flying hummingbird.HTTP://WWW.SCIENCEMAG.ORG/CGI/CONTENT/ABSTRACT/178/4066/1195?IJKEY=DD3819980CC11BD54B2042F16AA2A938C57230B5&KEYTYPE2=TF_IPSECSHA >TITLE=TEMPERATURE REGULATION BY THE INFLORESCENCE OF PHILODENDRON DATE = DECEMBER 1972PAGES=1195–1197 AUTHOR2=DANIEL K. ODELL LAST-AUTHOR-AMP=YES PMID=17748981, 4066, 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.JOURNAL, Thermogenesis in three Philodendron species (Araceae) of French Guiana, Marc, Gibernau, Denis, Barabé, 2000, Canadian Journal of Botany,weblink 10.1139/cjb-78-5-685, 78, 5, 685,

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 ergs, produce up to {{convert|57.7|°C|°F}}, 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.JOURNAL, Westhoff, Jacob, 9 Oct 2014, Behavioural thermoregulation and bioenergetics of riverine smallmouth bass associated with ambient cold-period thermal refuge, Ecology of Freshwater Fish, 10.1111/eff.12192, 25, 72–85, (File:smallhuddle.jpg|thumb|During cold weather many animals increase their thermal inertia by huddling.)Animals also engage in kleptothermy in which they share or even steal each other's body warmth. In endotherms such as batsJOURNAL, Arends, A, Bonaccorso, FJ, Genoud, M, 1995, Basal rates of metabolism of nectarivorous bats (Phyllostomidae) from a semiarid thorn forest in Venezuela, J. Mammal., 76, 3, 947–956, 10.2307/1382765, 1382765, and birds (such as the mousebirdJOURNAL, Brown, C. R., Foster, G. G., 10.1007/BF00296648, The thermal and energetic significance of clustering in the speckled mousebird, Colius striatus, Journal of Comparative Physiology B, 162, 7, 658–664, 1992, and emperor penguinJOURNAL, Ancel, A, Visser, H, Handrich, Y, Masman, D., Le Maho, Y, vanc, 1997, Energy saving in huddling penguins, Nature, 385, 6614, 304–305, 10.1038/385304a0, ) 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 loss.JOURNAL, Canals, M, Rosenmann, M, Bozinovic, F, 1989, Energetics and geometry of huddling in small mammals, J. Theor. Biol., 141, 2, 181–189, 10.1016/S0022-5193(89)80016-5, Some ectotherms share burrows of ectotherms. Other animals exploit termite mounds.JOURNAL, Ehmann, H, Swan, G, Swan, G, Smith, B, 1991, Nesting, egg incubation and hatching by the heath monitor Varanus rosenbergi in a termite mound, Herpetofauna, 21, 17–24, JOURNAL, Knapp, CR, Owens, AK, 2008, Nesting Behavior and the Use of Termitaria by the Andros Iguana (Cyclura Cychlura Cychlura), Journal of Herpetology, 42, 1, 46–53, 10.1670/07-098.1, Some animals living in cold environments maintain their body temperature by preventing heat loss. Their fur grows more densely to increase the amount of insulation. 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 {{convert|0|°C|°F}}. This minimizes heat loss through less insulated body parts, like the legs, feet (or hooves), and nose.File:wiki ostrich.jpg|thumb|An ostrichostrich

Hibernation, estivation and daily torpor

To cope with limited food resources and low temperatures, some mammals hibernate during cold periods. To remain in "stasis" for long periods, these animals build up brown fat reserves and slow all body functions. True hibernators (e.g., groundhogs) keep their body temperatures low throughout hibernation whereas the core temperature 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.Estivation is similar to hibernation, however, it usually occurs in hot periods to allow animals to avoid high temperatures and desiccation. Both terrestrial and aquatic invertebrate and vertebrates enter into estivation. Examples include lady beetles (Coccinellidae),JOURNAL, Kenneth S. Hagen, 1962, Biology and ecology of predaceous Coccinellidae, Annual Review of Entomology, 7, 289–326, 10.1146/annurev.en.07.010162.001445, North American desert tortoises, crocodiles, salamanders, cane toads,WEB,weblink Audubon Guides, Estivation: The Survial{{sic, n, Siesta |date=29 September 2009 |author=Bob Moore |deadurl=no |accessdate=24 October 2013}} and the water-holding frog.BOOK, F.H. Pough, R.M. Andrews, J.E. Cadle, M.L. Crump, A.H. Savitzky and K.D. Wells, 2001, Herpetology, second edition, Prentice Hall, Upper Saddle River, New Jersey, Daily torpor occurs in small endotherms like bats and hummingbirds, which temporarily reduces their high metabolic rates to conserve energy.BOOK, Biology: Concepts and Applications, Cecie, Starr, 2005, Thomson Brooks/Cole, 639, 978-0-534-46226-0,weblink

Variation in animals

(File:Body Temp Variation.png|thumb|250px|Chart showing diurnal variation in body temperature.)

Normal human temperature

Previously, average oral temperature for healthy adults had been considered {{convert|37.0|°C|°F|abbr=on}}, while normal ranges are {{convert|36.1|°C|°F|abbr=on}} to {{convert|37.8|°C|°F|abbr=on}}. In Poland and Russia, the temperature had been measured axillary. 36.6 Â°C was considered "ideal" temperature in these countries, while normal ranges are 36 Â°C to 36.9 Â°C.Recent studies suggest that the average temperature for healthy adults is {{convert|36.8|C|abbr=on}} (same result in three different studies). Variations (one standard deviation) from three other studies are:
  • 36.4–37.1 Â°C (97.5–98.8 Â°F)
  • 36.3–37.1 Â°C (97.3–98.8 Â°F) for males, 36.5–37.3 Â°C (97.7–99.1 Â°F) for females
  • 36.6–37.3 Â°C (97.9–99.1 Â°F)JOURNAL, Temperature of a Healthy Human (Body Temperature), Wong, Lena,weblink 2005, 10.1046/j.1471-6712.2002.00069.x, Scandinavian Journal of Caring Sciences, the Physics Factbook, 16, 122–128, 12000664, Forsberg, C, Wahren, LK, 2, yes, 24 October 2013,weblink" title="web.archive.org/web/20100926162224weblink">weblink 26 September 2010, dmy-all,
Measured temperature varies according to thermometer placement, with rectal temperature being 0.3–0.6 Â°C (0.5–1 Â°F) higher than oral temperature, while axillary temperature is 0.3–0.6 Â°C (0.5–1 Â°F) lower than oral temperature.BOOK,weblink Rectal, ear, oral, and axillary temperature comparison, Yahoo Health, The average difference between oral and axillary temperatures of Indian children aged 6–12 was found to be only 0.1 Â°C (standard deviation 0.2 Â°C),JOURNAL,weblink Comparison of Axillary Temperature with Rectal or Oral Temperature and Determination of Optimum Placement Time in Children, Indian Pediatrics, 41, 17 June 2004, 600–603, Deepti Chaturvedi, K.Y. Vilhekar, Pushpa Chaturvedi, M.S. Bharambe, 15235167, 6, and the mean difference in Maltese children aged 4–14 between oral and axillary temperature was 0.56 Â°C, while the mean difference between rectal and axillary temperature for children under 4 years old was 0.38 Â°C.JOURNAL,weblink How reliable is axillary temperature measurement?, E.C., Quintana, 43, 6, 797–798, June 2004, 10.1016/j.annemergmed.2004.03.010, Annals of Emergency Medicine,

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. Monkeys 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 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).{{sfn|Chisholm|1911|p=49}} Those diurnal temperatures can be reversed by reversing their daily routine.JOURNAL, 1465744, 1905, Simpson, S, An investigation into the diurnal variation of the body temperature of nocturnal and other birds, and a few mammals, The Journal of Physiology, 33, 3, 225–238, Galbraith, J. J, 16992810, 10.1113/jphysiol.1905.sp001124, In essence, the temperature curve of diurnal birds is 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, the curves obtained from rabbits, guinea pigs, and dogs were quite similar to those from man.{{sfn|Chisholm|1911|p=49}} These observations indicate that body temperature is partially regulated by circadian rhythms.

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 to 36.7 Â°C (97.6 to 98.1 Â°F). Within 24 hours of ovulation, women experience an elevation of 0.15–0.45 Â°C (0.2–0.9 Â°F) due to the increased metabolic rate caused by sharply elevated levels of progesterone. The basal body temperature ranges between 36.7–37.3 Â°C (98.1–99.2 Â°F) throughout the luteal phase, and drops down to pre-ovulatory levels within a few days of menstruation.BOOK,weblink Women's Sports Medicine and Rehabilitation, 978-0-8342-1731-7, Lippincott Williams & Wilkins, 2001, Swedan, Nadya Gabriele, 149, 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 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 where people without fever do not.

Variations due to biofeedback

Some monks are known to practice Tummo, biofeedback meditation techniques, that allow them to raise their body temperatures substantially.BOOK,weblink Meditation changes temperatures: Mind controls body in extreme experiments, William J., Cromie, Harvard Gazette, 2002,

Low body temperature increases lifespan

It has been theorised that low body temperature may increase lifespan. In 2006, it was reported that transgenic mice with a body temperature 0.3–0.5 C 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 to lower body temperature. Lifespan was increased by 12% and 20% for males and females, respectively. The mice were fed ad libitum.Transgenic Mice with a Reduced Core Body Temperature Have an Increased Life Span, by Bruno Conti et al. Science, 3, November 2006Reduced Body Temperature Extends Lifespan, Study FindsBee cool, live long 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.WEB,weblink OMIM entry on human UnCoupling Protein 2 (UCP2),

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 animal may endure and yet live. The effect of too extreme a cold is to decrease metabolism, and hence to lessen the production of heat. Both catabolic and anabolic 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 first, especially the brain and those parts concerning consciousness;JOURNAL, J. Physiol., 1905-05-09, 32, 5 Suppl 8, 305–11, The effect of cold narcosis on reflex action in warm-blooded animals, Simpson S, Herring PT, 16992777, 1465681, 10.1113/jphysiol.1905.sp001084, both heart rate and respiration rate decrease; judgment becomes impaired as drowsiness supervenes, becoming steadily deeper until the individual loses consciousness; without medical intervention, death by hypothermia quickly follows. Occasionally, however, convulsions may set in towards the end, and death is caused by asphyxia.{{sfn|Chisholm|1911|p=50}}In experiments on cats performed by Sutherland Simpson and Percy T. Herring, the animals were unable to survive when rectal temperature fell below 16 Â°C. 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, and the only certain sign that it had taken place was the loss of knee-jerks.{{sfn|Chisholm|1911|p=50}}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 by exhausting the metabolic capital of the respiratory centre;{{Citation needed|date=October 2009}} heart rate is increased; the beats then become arrhythmic and eventually cease. The central nervous system is also profoundly affected by hyperthermia and delirium, and convulsions may set in. Consciousness may also be lost, propelling the person into a comatose condition. These changes can sometimes also be observed in patients suffering from an acute fever.{{Citation needed|date=October 2009}} Mammalian muscle becomes rigid with heat rigor at about 50 Â°C, with the sudden rigidity of the whole body rendering life impossible.{{sfn|Chisholm|1911|p=50}}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 showed very similar temperature values, those from the Amphibia examined being 38.5 Â°C, fish 39 Â°C, reptiles 45 Â°C, and various molluscs 46 Â°C.{{Citation needed|date=October 2009}} Also, in the case of pelagic 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 protoplasm and, hence, greater variation in the extreme temperature compatible with life.{{sfn|Chisholm|1911|p=50}}

Arthropoda

The maximum temperatures tolerated by certain thermophilic arthropods exceeds the lethal temperatures for most vertebrates.WEB,weblink Mite sets new record as world's fastest land animal, Federation of American Societies for Experimental Biology (FASEB), 27 April 2014, Featured Research, ScienceDaily, 28 April 2014, 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 {{convert|50|°C|°F}}, for the carcasses of insects and other forms of life which have succumbed to heat stress.WEB,weblink Chapter 21: Most heat tolerant, Sherwood, Van, 1 May 1996, Book of Insect Records, University of Florida, 30 April 2014, 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 {{convert|60|°C|°F}}, 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.

See also

References

{{reflist|30em}}

Further reading

  • BOOK, 2001, First published 1998, Blatteis, Clark M, Physiology and Pathophysiology of Temperature Regulation, Singapore & River Edge, NJ, World Scientific Publishing Co, 978-981-02-3172-9,weblink 8 September 2010,
  • JOURNAL, 10.4065/78.5.603, May 2003, Charkoudian, Nisha, Skin Blood Flow in Adult Human Thermoregulation: How It Works, When It Does Not, and Why, Mayo Clinic Proceedings, 78, 5, 603–612,weblink 12744548, full pdf
  • {{EB1911|wstitle=Animal Heat|volume=2|pages=48–50}} This cites work of Simpson & Galbraith
  • BOOK, 1917, Green, Charles Wilson, Kirke's Handbook of Physiology, North American Revision, New York, William Wood & Co,weblink 8 September 2010, Other Internet Archive listings
  • BOOK, Guyton and Hall Textbook of Medical Physiology with Student Consult Online Access, Hall, John E., 2010, 12th, Elsevier Saunders, Philadelphia, 978-1-4160-4574-8, Arthur Guyton, 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).
  • BOOK, 1970, Hardy, James D, Gagge, A. Pharo, Stolwijk, Jan A, Physiological and Behavioral Temperature Regulation, Springfield, Illinois, Charles C Thomas,
  • JOURNAL, 1998, Havenith, George, Coenen, John M.L, Kistemaker, Lyda, Kenney, W. Larry, Relevance of individual characteristics for human heat stress response is dependent on exercise intensity and climate type, European Journal of Applied Physiology, 77, 3, 231–241, 10.1007/s004210050327, 9535584,
  • JOURNAL, 10.1109/10.914795, March 2001, Kakuta, Naoto, Yokoyama, Shintaro, Nakamura, Mitsuyoshi, Mabuchi, Kunihiko, Estimation of Radiative Heat Transfer Using a Geometric Human Model, IEEE Transactions on Biomedical Engineering, 48, 3, 324–331, 11327500, link to abstract
  • BOOK, 2008, Marino, Frank E, Thermoregulation and Human Performance: Physiological and Biological Aspects, Medicine and Sport Science, Vol.53, Basel, Switzerland, Karger, 978-3-8055-8648-1,weblink 9 September 2010,
  • JOURNAL, 1 June 1976, Mitchell, John W, Heat transfer from spheres and other animal forms, Biophysical Journal, 1276385, 16, 6, 561–569, 10.1016/S0006-3495(76)85711-6, 1334880,
  • BOOK, 1994, Milton, Anthony Stewart, Temperature Regulation: Recent Physiological and Pharmacological Advances, Switzerland, Birkhäuser Verlag, 978-0-8176-2992-2,weblink 9 September 2010,
  • JOURNAL, November 2001, Selkirk, Glen A, McLellan, Tom M, yes, Influence of aerobic fitness and body fatness on tolerance to uncompensable heat stress, Journal of Applied Physiology, 91, 5, 2055–2063,weblink 9 September 2010, 11641344, 10.1152/jappl.2001.91.5.2055, 1807/14121,
  • JOURNAL, 1905, Simpson, S., Galbraith, J.J, yes, 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, 10.1017/S0080456800011649,
  • BOOK, {{ill, Helmut Tributsch, de, (Author), Miriam Varon (Translator) |date=May 1985 |title=How Life Learned to Live: Adaptation in Nature |url= |location= |publisher=Mit Pr |page= |isbn=978-0262700283}}
  • 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}}.

External links

{{Library resources box|by=no|onlinebooks=no|others=no|about=yes|label=Thermoregulation}}

, Wong
, Lena
, Temperature of a Healthy Human (Body Temperature)
, The Physics Factbook
, yes
, 24 October 2013
, 1997
,weblink
,weblink" title="web.archive.org/web/20100926162224weblink">weblink
, 26 September 2010
, dmy-all
,
  • {{MeshName|Thermoregulation}}
{{Human homeostasis}}


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