In some animals, the body temperature remains constant and is independent of the environment. These animals are classified as homeothermic eg. birds and mammals. They can regulate their body temperatures by generating heat through metabolic activities. Hence they are also called as endothermic animals.
During summer, the environmental temperature shoots up. Warm blooded animals keep their hairs and feathers flat and close to the body so that there is no air between the body and hair. This permits loss of heat by radiation and prevents the entry of heat in to the body.
The sweat glands in the skin are stimulated to secrete sweat which evaporates, taking excess heat from the body, thereby reducing the body temperature. In dogs and cats panting helps to cool down the body temperature. Panting also speeds up evaporation from the lungs.
During winter, environmental temperature is low. The hairs and feathers are raised, so that air accumulates between the hair and the body surface.
This air gets warmed up by the body temperature. This layer of warmed air functions as an insulator to prevent heat loss from the body.
The blood vessels supplied to the skin become constricted in mammals. Hence blood supply to the skin is restricted. At the same time, blood vessels supplied to the main excretory organ namely, kidney become dilated. This results in excess urine formation.
Thus urine removes excess heat from the body to keep the temperature constant. This is true as in the case of human beings. Metabolic rate is also increased, so that a large amount of metabolic heat is produced to warm up the body.
Source : The Hindu