Thermoregulation

Thermoregulation

1. Poikilotherm

   • Invertebrates

2. Homeotherm

   • Mammals
     • Rectal/Oral Temperatures will not always directly reflect core body temperature (consider on v. cold days)
   • Birds
     • Air sacs
       • Gular flutter: birds equivalent of panting
   • High Metabolic Rate
   • Thermoneutral Zone
     • Range of temperature in which a homeotherm can regulate its body temperature by adjusting heat loss at negligible energy cost
     • Minimal metabolic rate and energy expenditure
     • Most production processes are most efficient
     • Animal is thermally comfortable
     • Critical temps

3. Mechanisms to Maintain Temp

   • Heat Production and Gain
     • Metabolism
       • Heat produced from oxidative metabolism of protein, fat and carbohydrates. Varies with; feed intake, muscular activity, thermal environment and size.
       • Body Size
         • Bigger
           • Lower metabolic rates
           • Stable core body temperatures
           • Heat loss becomes a problem
           • Migration
           • Low SA:V
     • Muscle Contraction
       • Shivering
       • Exercise
     • Non-Shivering Thermogenesis
       • From metabolism of fats.
     • Environment
   • Heat Loss
     • Non-evaporative heat loss to environment
       • Convection
       • Conduction
       • Radiation
     • Evaporative heat loss from body surface and respiratory system

4. Why Homeotherm/Poikilotherm? Factors to consider

   • Activity level
   • Dependance on environment
   • Metabolic rate vs energetic cost
   • Ambient temp variation
   • Behavioural Thermoregulation
   • Insulation

5. Heat Exchange with the Environment

   • Heat Gain
   • Sensible Heat Loss
   • Evaporative Heat Loss
   • Factors
     • Physical
       • Weather
         • temperature/air speed/rain and snow
       • Size/Shape
         • Warmer climate; - Thinner limbs - Shorter coat Colder climate; - Thicker limbs - Longer coat
       • Internal Insulation
         • Fat/blubber
       • Peripheral blood flow
       • Colour
     • Behavioural
       • - burrowing - sunbathing
       • Too hot?
         • Avoid sun
           • seek shade/burrow
         • Increase evaporative heat loss
           • Wallow/spray/lick fur
         • Increase non-evaporative heat loss
           • Postural changes
       • Too cold?
         • Reduce sensible heat loss
         • Shelter from wind and rain
         • "Freeze" to avoid water penetration
         • Huddle
         • Postural changes

6. Hibernation

   • Reduce activity
   • Live off fat and glycogen reserves
   • Let temp fall
     • reset hypothalamus
   • Slow rate of breathing

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