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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 thermoreegulation 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 55 °C (131 °F), and with prolonged exposure (longer than a few hours) at this temperature and up to around 75 °C (167 °F) death is almost inevitable.[citation needed] Humans may also experience lethal hyperthermia when the wet bulb temperature is sustained above 35 °C (95 °F) for six hours.[1] 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 37 °C (99 °F), and hypothermia sets in when the core body temperature gets lower than 35 °C (95 °F).[2] 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.[3]





Classification of animals by thermal characteristicsEdit

Endothermy vs. ectothermyEdit

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.[6] 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.[7] 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, have 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.[7][6]



Ectothermic coolingEdit

  • Vaporization:
  • Convection:
    • Increasing blood flow to body surfaces to maximize heat transfer across the advective gradient.
  • Conduction:
      • 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)Edit

  • Convection:
    • Climbing to higher ground up trees, ridges, rocks.
    • Entering a warm water or air current.
    • Building an insulated nest or burrow.
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.
Thermographic image of a snake around an arm





Homeothermy compared with poikilothermyEdit




Brain controlEdit

Thermoregulation in both ectotherms and endotherms is controlled mainly by the preoptic area of the anterior hypothalamus.[8] Such homeostatic control is separate from the sensation of temperature.[8]

In birds and mammalsEdit

Kangaroo licking its arms to cool down on a very hot day


  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 wolf[9] or penguins[10][11])


  2. Evaporative cooling by perspiration and panting

In humansEdit

Simplified control circuit of human thermoregulation.[12]

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.[13] 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.[14][15] For humans, adaptation to varying climatic conditions includes both physiological mechanisms resulting from evolution and behavioural mechanisms resulting from conscious cultural adaptations.[16][17] The physiological control of the body’s core temperature takes place primarily through the hypothalamus, which assumes the role as the body’s “thermostat.”[18] This organ possesses control mechanisms as well as key temperature sensors, which are connected to nerve cells called thermoreceptors.[19] 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.[20][21]

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.[22] During intense physical activity (e.g. sports), evaporation becomes the main avenue of heat loss.[23] Humidity affects thermoregulation by limiting sweat evaporation and thus heat loss.[24]

A dog panting after exercise

In plantsEdit

Thermogenesis occurs in the flowers of many plants in the Araceae family as well as in cycad cones.[25] In addition, the sacred lotus (Nelumbo nucifera) is able to thermoregulate itself,[26] 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,[27] which requires the consumption of oxygen at a rate approaching that of a flying hummingbird.[28]

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.[25] 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.[29]

Behavioral temperature regulationEdit


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 bats[31] and birds (such as the mousebird[32] and emperor penguin[33]) 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.[34] Some ectotherms share burrows of ectotherms. Other animals exploit termite mounds.[35][36]

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 0 °C (32 °F). This minimizes heat loss through less insulated body parts, like the legs, feet (or hooves), and nose.


Hibernation, estivation and daily torporEdit


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),[37] North American desert tortoises, crocodiles, salamanders, cane toads,[38] and the water-holding frog.[39]


Variation in animalsEdit

Chart showing diurnal variation in body temperature.

Normal human temperatureEdit



  • 36.4–37.1 °C (97.5–98.8 °F)
  • 36.3–37.1 °C (97.3–98.8 °F) for males, 36.5–37.3 °C (97.7–99.1 °F) for females
  • 36.6–37.3 °C (97.9–99.1 °F)[41]

Measured 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.[42] The average difference between oral and axillary temperatures of Indian children aged 6–12 was found to be only 0.1 °C (standard deviation 0.2 °C),[43] and the mean difference in Maltese children aged 4–14 between oral and axillary temperature was 0.56 °C, while the mean difference between rectal and axillary temperature for children under 4 years old was 0.38 °C.[44]

Variations due to circadian rhythmsEdit

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).[5] Those diurnal temperatures can be reversed by reversing their daily routine.[45]

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.[5] These observations indicate that body temperature is partially regulated by circadian rhythms.

Variations due to women's menstrual cyclesEdit

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 °C (97.6 to 98.1 °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 (98.1–99.2 °F) throughout the luteal phase, and drops down to pre-ovulatory levels within a few days of menstruation.[46] Women can chart this phenomenon to determine whether and when they are ovulating, so as to aid conception or contraception.

Variations due to feverEdit


Variations due to biofeedbackEdit


Low body temperature increases lifespanEdit

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.[48][49][50] 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.[51]

Limits compatible with lifeEdit




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 °C, fish 39 °C, reptiles 45 °C, and various molluscs 46 °C.[citation needed] 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.[53]


The maximum temperatures tolerated by certain thermophilic arthropods exceeds the lethal temperatures for most vertebrates.[54]



See alsoEdit


  2. ^ "Hypothermia". Mayo Clinic. Retrieved 2017-05-01. 
  3. ^ "Hypothermia: Causes, Symptoms, and Treatment". WebMD. Retrieved 2017-05-01. 
  4. ^ Chisholm 1911, p. 48.
  5. ^ a b c d Chisholm 1911, p. 49.
  6. ^ a b "Khan Academy". Khan Academy. Retrieved 2017-04-03. 
  7. ^ a b Boundless (2016-09-20). "Homeostasis: Thermoregulation". Boundless. 
  8. ^ a b Romanovsky, AA (2007). "Functional architecture of the thermoregulatory system". Am J Physiol Regul Integr Comp Physiol. 292 (1): R37–46. doi:10.1152/ajpregu.00668.2006. PMID 17008453. 
  9. ^ Swan, K. G.; R. E. Henshaw (March 1973). Lumbar sympathectomy and cold acclimatization by the arctic wolf. Analysis of Surgery. 177. pp. 286–292. doi:10.1097/00000658-197303000-00008. PMC 1355529 . PMID 4692116. 
  12. ^ 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. doi:10.1007/s00421-009-1256-6. 
  14. ^ "Heat Exhaustion: Symptoms and Treatment". WebMD. Retrieved 2017-03-01
  15. ^ Harmon, Katherine. "How Does a Heat Wave Affect the Human Body?". Scientific American. Retrieved 2017-03-01
  18. ^ "Thermoregulation". Retrieved 2017-03-01.
  19. ^ Boundless (2016-05-26). "Thermoreception". Boundless.
  20. ^ 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.
  21. ^ "Temperature Regulation of the Human Body". Retrieved 2017-03-01.
  22. ^ Guyton & Hall (2006), pp. 891–892
  25. ^ a b Minorsky, Peter V. (May 2003). The Hot and the Classic. Plant Physiol. 132. pp. 25–26. doi:10.1104/pp.900071. PMC 1540311 . PMID 12765187. 
  28. ^ Kenneth A. Nagy; Daniel K. Odell & Roger S. Seymour (December 1972). Temperature Regulation by the Inflorescence of Philodendron. Science. 178. pp. 1195–1197. doi:10.1126/science.178.4066.1195. PMID 17748981. 
  29. ^ Gibernau, Marc; Barabé, Denis (2000). Thermogenesis in three Philodendron species (Araceae) of French Guiana (PDF). Canadian Journal of Botany. 78. p. 685. doi:10.1139/cjb-78-5-685. 
  30. ^ Westhoff, Jacob (9 Oct 2014). "Behavioural thermoregulation and bioenergetics of riverine smallmouth bass associated with ambient cold-period thermal refuge". Ecology of Freshwater Fish. 25: 72–85. doi:10.1111/eff.12192. 
  31. ^ 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: 947–956. doi:10.2307/1382765. 
  32. ^ Brown, C. R.; Foster, G. G. (1992). "The thermal and energetic significance of clustering in the speckled mousebird, Colius striatus". Journal of Comparative Physiology B. 162 (7): 658–664. doi:10.1007/BF00296648. 
  33. ^ Ancel A, Visser H, Handrich Y, Masman D, Le Maho Y (1997). Energy saving in huddling penguins. Nature. 385. pp. 304–305. doi:10.1038/385304a0. 
  34. ^ Canals, M; Rosenmann, M; Bozinovic, F (1989). "Energetics and geometry of huddling in small mammals". J. Theor. Biol. 141: 181–189. doi:10.1016/S0022-5193(89)80016-5. 
  35. ^ 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. 
  36. ^ 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. doi:10.1670/07-098.1. 
  41. ^ Wong, Lena; Forsberg, C; Wahren, LK (2005). "Temperature of a Healthy Human (Body Temperature)". Scandinavian Journal of Caring Sciences, The Physics Factbook. 16 (2): 122–128. doi:10.1046/j.1471-6712.2002.00069.x. PMID 12000664. Retrieved 24 October 2013. 
  42. ^ Rectal, ear, oral, and axillary temperature comparison. Yahoo Health. 
  43. ^ Deepti Chaturvedi; K.Y. Vilhekar; Pushpa Chaturvedi; M.S. Bharambe (17 June 2004). "Comparison of Axillary Temperature with Rectal or Oral Temperature and Determination of Optimum Placement Time in Children" (PDF). Indian Pediatrics. 41 (6): 600–603. PMID 15235167. 
  44. ^ Quintana, E.C. (June 2004). How reliable is axillary temperature measurement?. Annuals of Emergency Medicine. 43. pp. 797–798. doi:10.1016/j.annemergmed.2004.03.010. 
  49. ^ Reduced Body Temperature Extends Lifespan, Study Finds
  50. ^ Bee cool, live long
  51. ^ "OMIM entry on human UnCoupling Protein 2 (UCP2)". 
  52. ^ a b c Simpson S, Herring PT (1905-05-09). "The effect of cold narcosis on reflex action in warm-blooded animals". J. Physiol. 32 (5 Suppl 8): 305–11. doi:10.1113/jphysiol.1905.sp001084. PMC 1465681 . PMID 16992777. 
  53. ^ a b c d Chisholm 1911, p. 50.

Further readingEdit

External linksEdit