body temperature and heat regulation dr than kyaw 23 oct 2011
TRANSCRIPT
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