Any significant variation in the internal temperature could have damaging effects on the body's enzymes. Homeotherms or warm-blooded animals including human can however generate conserve heat in a certain range within the body and are therefore mainly independent of environmental temperature. Heat can be gained or lost from the body in four ways.
Radiation -transfer of heat to or from the body to other objects via the air
Conduction- transfer of heat to or from the body by direct contact with another object, radiator or window
Convection- transfer of heat to or from the body via moving air
Evaporation- the loss of heat used to change water from a liquid to a vapour e.g. when water leaves the skin surface or gas exchange system.
Body temperature is controlled by the thermo-regulatory centre in the hypothalamus, the hypothalamus in the brain acts as a thermostat and is sensitive to changes in blood temperature. If the temperature of the blood entering the hypothalamus falls, it sends impulses to organ causing them to reduce heat loss. The reverse happens if the temperature of the blood entering the hypothalamus rises. The temperature of the hypothalamus can be taken by placing a temperature probe down the outer ear so that it touches the eardrum. Periodically the person drank a quantity of ice cold water, the internal body temperature dropped.
Behavioral control of the body temperature although humans show many physiological changes when the environmental temperature varies , behavior also plays an important part in maintaining a constant body temperature, in cold weather we eat more put more clothing on and haggle together, in hot weather we take off layers of clothing we drink more and have cold shower.
Response to heat gain sweating evaporates using heat from the skin, the skin is in contact with the environment and is therefore essential in thermoregulation in very cold conditions the body must minimize its heat lost, this has a cooling effect sweat glands extracts more fluid from the blood. Reaction of hairs on the skin hair erector muscle relaxed therefore the hair lies flat. Very little air is trapped so little insulation provided. Vasodilation and dilation of shunt vessels more blood in the circulation blood which is stored in the liver and spleen is released into the circulation. More blood therefore reaches the skin surface, therefore more heat is lost.