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Communication and homeostasis
Control of body temperature
Animals are classed as either ectotherms or endotherms, depending on how they control
their body temperature
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Example – a lizard is an ectotherm
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When its internal temperature gets too low it will move
to somewhere cooler such as a burrow beneath the sand
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Ectotherms have a variable metabolic rate as they can’t keep their internal environment
constant
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They’re more active at higher temperatures
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Example – an elephant is an endotherm
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The internal temperature of endotherms is less affected by external temperature as
opposed to ectotherms
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They generate a
lot of heat from metabolic reactions
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Mechanisms to reduce body temperature
 Sweating - more sweat is secreted from sweat glands when the body is too hot
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The skin is cooled
 Hairs lie flat – mammals have a layer of hair that provides insulation by trapping air
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Less air is trapped,
so the skin is less insulated and heat can escape the body
 Vasodilation – when it’s hot, arterioles near the surface of the skin dilate
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Mechanisms to increase body temperature
 Shivering – muscles contract in spasms
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These increase metabolism
so heat is produced
 Much less sweat – less sweat is secreted from glands, reducing heat loss
 Hairs stand up – erector pili muscles contract when it’s cold, this makes the hairs
stand up
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This reduces heat loss
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The
hypothalamus receives information about internal and external temperatures from
thermoreceptors
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Thermoreceptors send impulses along sensory neurones to the hypothalamus, which sends
impulses along motor neurones to the effectors

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