c
             When an endotherm is subjected to severe cold it is liable to lose heat energy but this can be counteracted in a number of ways;
             „h It could raise the hairs into a more vertical position by the contraction of the erector pili muscles. Air can then be trapped in the spaces between the hairs and, being a poor conductor of heat, it serves as an insulatory layer round the animal. This is an involuntary response brought about by the nervous system.
             „h The arterioles leading to the superficial capillaries constrict and as a result blood flow to the surface of the skin is greatly reduced (vasoconstriction). This is brought about by the sympathetic nervous system and is useful in uncovered regions such as the ears where th
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