Explain how human body temperature is maintained by homeostasis?

When the external environment is hot, the temperature is detected by temperature receptors on the skin, which is transmitted to the brain via the sensory neurons. The brain sends the signals to the hypothalamus, which sends signals to the blood vessels, skin and hair. The blood vessels will vasodilate and the sweat glands will produce sweat. Vasodilation allows evaporation of the sweat from the skin, which takes up heat from the blood. The hair on the skin also lies flat, which further reduces insulation. When the external environment is cold, the blood vessels will vasoconstriction preventing heat loss by evaporation. The hair on the skin will stand erect, which allows for insulation. Finally, the sweat glands do not produce sweat, preventing further heat loss. As the same organs are dealing with two extreme conditions by reversing the process, this is called negative feedback mechanism.