Body Temperature and Heat Regulation Dr Than Kyaw 23 Oct 2011

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 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 Body Temperature

Normal body temperatures of some animals Body Temperature Animal °C°FRange °CRange °F Beef cow – – Dairy cow – – Sheep – – Dog – Cat – – Pig – – Chicken (day light) – Stallion – – Mare – – 100.8

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 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 Body Temperature

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 1.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

Thermal regulation - 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 Circulatory adjustment Warm/ cold Thermoreceptors on the skin Thermoregulatory center in hypothalmus impulse Vasoconstrictors on the b/v of the skin

Thermal regulation -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 Evaporative heat loss Latent heat ? sweating & panting

Thermal regulation -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 Evaporative heat loss

Apocrine sweat glandEccrine sweat gld:

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

Thermal regulation - 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% - Pig cannot 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 Responses to extremes of heat

Thermal regulation -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 Responses to extremes of heat

Thermal regulation -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 arrector pili muscle - hair coat thickened and the amount of s/c fat increased Responses to cold

Thermal regulation -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. Responses to cold

Thermal regulation -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 Responses to cold

Thermal regulation -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 Hibernation

Thermal regulation -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 Awakening from Hibernation

Thermal regulation -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 Brown fat versus white fat

-Brown fat facilitates the arousal of hibernated animals (non-shivering thermogenesis) -Brown fat cells are stimulated – consume O 2 and produce heat at high rate Thermal regulation Brown fat versus white fat

-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) 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 Thermal regulation Hypothermia

-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 Thermal regulation Hyperthermia

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

End of Lecture Thank You