Describe the functioning of the heart in terms of the contraction of muscles of the atria and ventricles and the action of the valves in a heartbeat

Explain how each of the following processes contributes to the maintenance of constant internal body temperature in mammals: (a) sweating (b) shivering (c) contraction of hair erector muscles (d) vasodilation and vasoconstriction of arterioles supplying skin surface capillaries