Sweating, vasodilaton and casoconstriction, hair erection, and shivering act together to keep the body temperature to within a few tenths of a degree to the normal 37 degrees Celsius.
If the body temperature is too hot, (this can be detected by he hypothalamus) the sweat glands produce greater amounts of sweat. This liquid is secreted onto the surface of the skin. When a liquid is evaporated it turns into a gas, and this change requires energy called the latent heat of vapourisation. When sweat evaporates, the energy is supplied by the bodies heat cooling the body down.
Also, in cold conditions the hair erector muscles at the base of the hair on you skin, contract and the hairs are pulled upright. this traps a layer of air next to the skin, and since air is a poor conductor of heat, this acts as insulation
There are tiny blood vessels called capillary loops in the dermis. Blood flows through these loops radiating heat to the outside, and cooling the body down. if the body is too hot small arteries (arterioles) leading to the capillary loops dilate (widen). This increases blood flow to the skins surface and is called vasodilation.
In cold conditions the opposite happens. the arterioles leading the the surface capillary loops constrict ( become narrower) and blood flow to the skin id reduced, so that less heat is lost. This is called vasoconstriction.
Shivering also takes place in cold conditions, it is when the muscles relax and contract rapidly. This generates a large amount of heat.
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