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Not all organisms maintain their body’s core temperature the same way. Some control it internally like we do. We’re endothermic. Reptiles for example are not. They’re ectothermic. Two pennies for who guesses how these fine specimens maintain their temperature. Do they:
A) Run for heat?
B) Shiver for heat?
C) Sit where the sun shines?
They sit where the sun shines, ladies and gentlemen, they just sit there until it gets too hot. And what do they do when it gets too hot? Well, funny you should ask. They move their scaly little selves to a shady place. Why didn’t our monkey-faced ancestors think of that? (They did, long story.)
Needless to say, a lot of ectothermic organisms live in extremely stable regions where temperature doesn’t fluctuate wildly.
Fun fact: that bit in the brain, the hypothalamus, is responsible for temperature homeostasis. Thermoreceptors pick up increases and decreases in optimal body temperature and send signals to effectors to act. This is what happens:
Sweat cools down the body by producing water that upon evaporation removes heat energy. Vasodilation is the dilation of blood vessels. It results in the distance between them and the skin shortening so that excess heat can dissipate quicker. Flat hairs ensure that no air is trapped close to the skin. Air is a poor heat conductor so effectively this removes any potential insulation.
No sweat occurs. Vasoconstriction has the opposite effect to vasodilation, as the vessels tighten up instead of dilate to prevent heat loss. Raised hairs create a layer of air trapped between hairs and skin, minimising heat loss to the environment. Shivering causes muscles to do work, thus releasing more heat. Hormones like adrenaline may be released to increase metabolism.