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What is body temperature

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What is body temperature

  1. 1. WHAT IS MEAN BODY TEMPERATURE?• Very different for different animalsWHY?Regional differences - core body temperatureHottest region - lumen of stomach +upper part small intestine - distinctly hotter thanaortic blood(Grayson, 1983) - not due - digestive orabsorptive functions - nor to metabolism
  2. 2. Estimates of body temperature (steady-state conditions)Tb = (a1 x Tcore) + (a2 x Tskin)a factors = empirically determined contributionsof core & shell to mean body temperatureSome estimates : 9:1 and 6: 4Varies with thermal environment and investigator•Tb = 0.67 Tre + 0.33 TskinWhich thermal sensors are important?
  3. 3. How do you determine mean surfacetemperature?Humans:Tskin = 0.07Tfeet + 0.32Tlegs + 0.18Tchest + 0.17Tback + 0.14Tarms + 0.05Thand + 0.07TheadPeriphery - skin, mucous surfaces (mouth, nose)Core - spinal cord, hypothalamus, medulla oblongata, +Difficult - determine by experiment - which are
  4. 4. Chicken - exposed cold Ta -shivers before change in deep body temperatureSuggests - heat production - controlled by thermalKuhnen and Jessen - 1988 - goat Change - skin temperature - alone - alters MR
  5. 5. 1 Populations of Temperature Sensitive Structures(skin, spinal cord, hypothalamus)4. Warm sensors - activity increases with local temperature increase No discharge at skin temperature below 30 C Receptors discharge with increase temperature from 30 >> 35 C• But little sustained activity Further increase - skin temperature >> increased sustained discharge that changes with temperature Peak activity - 45-47 C Activity ceases at higher temperature
  6. 6. 1. Cold Sensors - activity decreases over same temperature range Most active at 15 - 35 C & peak at 20 - 30 C===========================================================PARADOXICAL RESPONSE Most cold receptors >> no discharge above 35 C But may get discharge near noxious level (43 - 47 C) (ex. sudden chill - stepping into hot shower) Also paradoxical warm receptor response - BUT not as common
  7. 7. Proportions - cold & warm sensors - vary with siteIn general - more warm sensors - hypothalamus more cold sensors - cutaneous regionsExceptions - scrotal region - high concentration warm sensors Sheep & rats - local heating scrotum >> powerful heat loss effector activity If sustained >>> decrease in body temperature Heating scrotum - ram - above 36 C >> panting & decrease core body temperature (~ 2 C) Similiar effects - heating mammary skin - ewe
  8. 8. General facts about skin temperatureNot homogenous - large difference in skin temperature indifferent parts of the bodyMay account for regional differences by averaging surface area•BUT - density of skin thermoreceptors are different indifferent areasLarger weight to face and less to extremities •Face - approx. 20% of total skin signal
  9. 9. Skin temperature - represents interaction between convective heat exchange to surface by blood + removal of heat (geometry, external insulation, ambient temperature)Virtually all skin areas - including trunk -constrict at cold Ta(Exception = human forehead - no vasoconstriction at cold Ta)
  10. 10. CENTRAL RECEPTORSUnder normal conditions - trunk sites do not ary more than 0.5°CArterial temperature (e.g., carotid) - contain coreHypothalamus - contains many neurons andPreoptic Anterior Hypothalamus (POAH) still a lack box
  11. 11. During heat stress and exercise - may maintain brain temperature below trunkIn panting carnivores - blood supply passes through carotid rete A net-like structure - base of brainNumerous small arteries embedded in cavernous sinusRete = heat exchanger
  12. 12. •Cooled venous blood - evaporating surfaces (e.g., nasal mucosa)•arterial blood entering brain•running antelope - brain temperature ~3°C below carotid temperature•Also goat and sheep•maintenance of lower brain temperature also found in species without carotid rete (rabbit, squirrel, monkey, man)•Nonpanting animals - cool venous blood - sweating faceSite of exchange with arterial blood - unknown

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