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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
- Evaporation of water
