Increase in temperature: the body responds by dilating blood vessels (vasodilation) so that heat is lost via radiation through the skin and this is why we appear red, sweating in order to lose heat via evaporation and our body hair lies flat to prevent trapping air.Decrease in temperature: the body responds by constricting blood vessels (vasoconstriction) to try to conserve heat in the body, our muscles tense to make us shiver in order to generate more heat and our body hairs stand on end to trap a layer of air to conserve body heat.Why this is important: if our body temperature changes from the optimum too much, then the enzymes in our body could denature and lose their function.