Body temperature needs to remain constant. If it gets too low, the body will start to shiver, too high and the body will sweat.
The process of controlling body temperature requires temperature receptors in the skin, Receptors in the brain and effectors. (sweat glands and muscles)
Vasodilation and Vasoconstriction
Blood temperature is measured by a part of your brain called the hypothalmus.
When you are hot blood vessels in the skin dilate and alow more blood flow through the capillaries. This means that more heat is lost through the surface of the skin - vasodilation.
In cold condition, blood vessels in the skin constrict, reducing the amount of blood flow and heat is lost from the surface, causing us to shiver - this is called vasoconstriction.