When the body is cold
1. The small capillaries near the surface of the skin constrict (vasoconstriction) so less blood flows nearer to the surface, and less heat is lost through he blood.
2. The hairs on the skin stand erect by the hair erector muscles tightening. The hairs trap a layer of insulating air therefore less heat is lost to the surroundings.
3. Sweat Glands produce less sweat so less heat is lost through evaporation.
The muscles also vibrate very quickly when it is cold, so heat is produced to keep the body temperature at the correct level. This is also known as shivering!
When the body is hot
1. The small capillaries near the surface of the skin dilate (vasodilation) so more blood flows nearer to the surface, and more heat is lost through he blood. The body therefore cools down.
2. The hairs on the skin lie flat because the hair erector muscles slacken. No layer of insulating air is trapped therefore heat can be lost more easily.
3. Sweat Glands produce more sweat so more heat can be lost through evaporation.