An endotherm is an organism that can use internal sources of heat, such as heat generated from metabolism in the liver, to help maintain their body temperature. It can use behavioural mechanisms as well as physiological mechanisms to do this. An advantage to endothermy is that an organism, usually mammals and birds, can maintain a fairly constant body temperature despite the external temperature. Some of the physiological components involved to maintain body temperature are: sweat glands in the skin, lungs, mouth, and nose, hairs on skin and arterioles leading to capillaries in the skin. Examples of the behavioural mechanisms are when an organism feels too hot are: moves into shade or hides in a burrow orientates body to decrease surface area exposed to sun and remains inactive. If the organism feels cold, it will carry out the opposite behavioural mechanisms.