• Mechanisms for Heat loss

    • Evaporation of water
      • (i.e. sweating)
    • Loss of heat to the environment
      • Through conduction (e.g. from the ground)
      • Through convection (e.g. to the surrounding air or water)
      • Radiation
    • Vasodilation
      • Diameter of arterioles near surface are made larger
      • Increases volume of blood reaching the skin surface through the capillaries
    • Increased Sweating
      • Evaporate more water from the skin surface requires (heat) energy
      • Occurs on skin in skin only animals and on paws/tongue on fur animals
    • Lowering of body hair
      • Hair erector muscles in skin relax and elasticity of the skin so hair lowers
      • Reduces thickness of layer of still air
    • Behavioural Mechanism:
      • Avoiding the heat of the day by sheltering
      • Seeking out shade

    Mechanisms for Heat gain

    • Production of heat
      • Through metabolism of food during respiration
    • Gain of heat from the environment
      • Through conduction (e.g. from the ground)
      • Through convection (e.g. to the surrounding air or water)
      • Radiation
    • Vasoconstriction
      • Diameter of arterioles near surface are made smaller
      • Reduces volume of blood reaching the skin surface through the capillaries
      • Most of the blood entering the skin therefore passes beneath the insulating layer of fat and so loses less heat
    • Shivering
      • Muscles of the body undergo involuntary rhythmic contractions which produces metabolic heat
    • Raising of hair
      • Hair erector muscles in skin contract and so hair raises
      • Enables a thicker layer of still air which forms a layer of insulation
    • Increased metabolic rate
      • More of the hormones that increase metabolic rate are produced
      • As a result, metabolic activity, including respiration is increased and so more heat is generated
    • Decrease in Sweating
      • In cold conditions sweating ceases
    • Behavioural Mechanisms
      • Sheltering from the wind
      • basking in the sun
      • huddling together

    Endo/ectotherms

    • Birds and mammals are endotherms as they derive most of their heat from metabolic activity
    • All other animals are ectotherms as they obtain their heat from sources outside their body

    Control of Body Temperature

    • The change in temperature is detected by thermoreceptors
    • The receptors pass to the hypothalamus (coordinator) which is located in the brain
    • It results in the effectors in the skin to yield a response
    • Within the hypothalamus there are thermoregulatory centres of which:
      • Heat gain centre: activated by a fall in blood temperature. It controls mechanisms that increase body temperature
      • Heat loss centre: activated by an increase in blood temperature. It controls mechanisms that decrease body temperature
    • Hypothalamus measures blood temperatures running through it
    • Thermoreceptors measure temperature at the skin. They send impulses along the autonomic nervous system to the hypothalamus