Temperature receptors in the skin to detect the external temperature.
The brain in homeostasis
The brain which acts as a processing centre, to recieve information from the temprature receptors, responding by triggering the effectors.
Sweat glands and muscles carry out the automatic response.
What happens when body temperature is too high?
When you are too hot you sweat so it evaporates from the skin to cool you down. Also in hot conditions, blood vessels in the skin dilate, allowing more blood to flow through the skin capillaries. This means that more heat is lost from the surface of the skin by radiation. This is called vasodilation