Body Temperature and Heat Regulation

1. Body Temperature and Heat Regulation Dr Than Kyaw 23 Oct 2011

2. Body Temperature • Chemical reactions of the body - Heat production (Metabolism) Remember energy release by combustion of glucose • Body heat - continuous production • Maintaining constant body temperature – important to avoid fluctuations in body functions due to temperature changes Homeotherm (warm blooded animals) - mammals and birds Poikilotherm (cold blooded animals) – frogs, reptiles

3. Body Temperature • Body temperature measurement – obtained by rectal insertion of a thermometer at resting period • Factors influencing body temperature - exercise (work) - time of day - environmental temperature - digestion - drinking of water

4. Body Temperature Normal body temperatures of some animals

5. Body Temperature • Different part of the body – different temperature – differences in metabolic rate - blood flow - distance from the surfafe • Core temperature (deep body temperature) – higher than temperature of the limbs; may be higher than rectal tempt • Why rectal tempemperature? – represents steady state of the temperature

6. Body Temperature • - Diurnal temperature– temperature variation related to the time of the day • - Animal active during the day, sleep at night – lower tempt in the morning than in the afternoon • - Nocturnal animals – the opposite is true

7. Thermal regulation - Body heat constantly producing – if not provided for losing heat, the body tempt will increase to intolerable level • 2 ways of heat loss • Sensible heat loss – radiation - conduction - convection 2. Insensible heat loss – evaporation 25% Excretion of feces and urine – considered as a way of heat loss About 75% of body heat is dissipated

8. Thermal regulation Circulatory adjustment - Skin – excessive network of blood capillaries - Circulating blood – brought to the skin surface; heat loss to the environment - cold - vasoconstriction – heat loss reduced; conserve heat - controlled by sympathetic nerves Thermoreceptors on the skin impulse Warm/ cold Thermoregulatory center in hypothalmus Vasoconstrictors on the b/v of the skin impulse

9. Thermal regulation Evaporative heat loss Latent heat ? sweating & panting • Evaporation of water – insensible water loss - cooling • Water loss – from skin surface • - from lung (heated exhaled air) • 25% of heat loss by insensible mean at resting state

10. Thermal regulation Evaporative heat loss • Heat loss by sweating – less effective in domestic animals • than in man • Apocrine sweat gld • - situated at the hypodermis layer; • - the duct open into the hair follicle together with duct of sebaceous gland • - characteristic animal odour arise from bacterial action on apocrine secretion • Eccrine sweat gld: Typically found in human • - sparse in animal • - a few on foot pad of dog and cat

11. Apocrine sweat gland • Eccrine sweat gld:

12. Thermal regulation Evaporative heat loss Heat loss from sweating in order - Horse – greatest - cattle - sheep - dog - cat - swine Evaporative loss by panting - most effective in dog - some effect in cattle by increased salivation

13. Thermal regulation Responses to extremes of heat • - Ability to withstand extreme heat – differ in different spp • Cattle & sheep most able to withstand extremes of heat • tempt – open mouth panting + sweating – upto 43° C (109° F) with humidity above 65% • - Pigcannot tolerate – above 35° C (95° F) with humidity above 65% • - small mouth (ineffective panting) • - thick subcutaneous tissue • - scanty of sweat gland • - transport of pig – night time; need to hose with water

14. Thermal regulation Responses to extremes of heat • Cat – panting + spreading saliva over its hair coat • – cannot withstand 40° C (104° F) with humidity 65% • Dog - effective panting – tolerable than cat • Birds – closeness air sacs to the internal organs – likely facilitates • heat reduction/cooling • - body temperature 41° C (106° F) • - exposure to an air tempt of 38° C (100° F) and • humidity above 75% -- unsafe

15. Thermal regulation Responses to cold • Cold – activates body heating mechanisms • Excess cooling – (1) conserved heat by reducing heat loss • -- (2) generate heat to compensate for that which • is lost • Reducing heat loss • - curling up (reduce surface area exposed to cold) • - piloerection (to increase the insulation value of their coat/fur) • - the hair more erect by the action of arrectorpili muscle • - hair coat thickened and the amount of s/c fat increased

16. Thermal regulation Responses to cold • Peripheral v/s constricted by an increase in vasoconstrictor tone • Countercurrent heat transfer system in the limbs • Closeness of artery (blood warm, coming from heart) and vein (blood cold, coming from limbs) – heat is conserved by transferring from artery to vein.

17. Thermal regulation Responses to cold • Increased heat production • When reducing heat loss inadequate to maintain body temperature • Critical temperature • -the temperature to which body temperature decreases before • heat generation begins • - cattle and sheep – lowest critical temperature • - more suited to withstand cold • Shivering • Generalized rhythmic contraction of muscles • 30 to 50% of the energy of muscle contraction • – converted to heat

18. Thermal regulation Hibernation • The act of resting dormant state in a protected burrow • Characteristics of hibernation • 1. a process of warm blooded animals • 2. autonomous process – the animal induces and reverses it by self contained mechanism • 3. changes involve not only overt physiological functioning but also cellular and subcellular changes • 4. all physical functions continues – but at a reduced rate • 5. body temperature lowered significantly to a level compatible with survival of the species

19. Thermal regulation Awakening from Hibernation • Periodically awake from their dominant state • e.g. Kidneys continue to form urine and the animal has a need • to urinate • - If body temperature decline to near freezing – the animal awakes and rapidly rewarms

20. Thermal regulation Brown fat versus white fat • A connective tissue with a colour resulted from cytochrome pigments and a high density of mitochondria • Typically found in hibernating animals and in smaller species • Also in newborn of many species and disapears within a few months of life • Usual locations • - subcutaneous region between scapulae • - in the regions of kidneys • - within myocardium

21. Thermal regulation Brown fat versus white fat • Brown fat facilitates the arousal of hibernated animals (non-shivering thermogenesis) • Brown fat cells are stimulated – consume O2 and produce heat at high rate

22. Thermal regulation Hypothermia • Reduction of deep body temperature below normal temperature • Occurs as a result of prolong exposure to cold • Inability of heat conserving and heat generating mechanisms to keep pace • Tolerance to lowered body temperatures vary with species • Dog - 25° C (77° F); chicken 38° C (100° F)

23. Thermal regulation Hypothermia • Anaesthetized animal may suffer from hypothermia as the hypothalamus (heat regulatory center) is depreesed • External heat must be provided for hypothermic animals

24. Thermal regulation Hyperthermia • Heat production exceeds evaporative capacity of the environment and occurs when humidity is high • Hyperthermia may result from impaired evaporative mechanisms due to loss of body fluid, or reduced blood volume • Hyperthermia may accompany with heat stroke • Antipyretics - no effect on heatstroke animal • Whole body cooling – the only treatment to relieve heat stroke

25. What is thermal neutral zone? • Lower critical temperature • Upper critical temperature Upper critical temperature Lower critical emperature thermal neutral zone Minimal heat Production and heat loss Heat production Heat loss

26. End of Lecture Thank You