Body Temperature and Heat Regulation

Dr Than Kyaw23 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 °F Range °C Range °FBeef cow 38.3 101 36.7 – 39.1 98.0 – 102.4Dairy cow 38.6 101.5 38.0 – 39.3 100.4 – 102.8Sheep 39.1 102.3 38.3 – 39.9 100.9 – 103.8Dog 38.9 102 37.9 -39.9 100.2 – 103.8Cat 38.6 101.5 38.1 – 39.2 100.5 – 102.5Pig 39.2 102.5 38.7 – 39.8 101.6 – 103.6Chicken (day light) 41.7 107.1 40.6 - 43 105 – 109.4

Stallion 37.6 99.7 37.2 – 38.1 99 – 100.6Mare 37.8 100 37.3 – 38.2 99.1 – 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 loss1. 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

impulseVasoconstrictors 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 gland Eccrine sweat gld:

Thermal regulation

Evaporative heat lossHeat 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 O2 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 zoneLower critical emperature

Upper critical temperature

Minimal heat Production and heat loss Heat lossHeat production

End of Lecture

Thank You