The hypothalamus detects slightest changes in internal temperature as blood flows in the brain and send impulses to appropriate responding organs/tissues to bring it back to normal level. These organs include the skin, liver and muscles.
Parts of skin involved in thermoregulation are the sweat glands,as temperature increases sweat glands are stimulated to release sweat. As the water in sweat evaporates,it absorbs heat from the body ( latent heat of vaporization) through radiation and convectional current. When the body temperature decreases, the blood vessels in the skin constricts( vasoconstriction). This reduces blood flow to the skin hence less heat is lost to the internal environment.
Metabolic activities of the liver and muscles increase to raise heat production when the body temperature is low