2.89 describe the role of the skin in temperature regulation, with reference to sweating, vasoconstriction and vasodilation

When you are cold (and need to warm up)
- Blood vessels near the surface of the skin constrict (tighten) so that less heat can be transferred from the blood to the surroundings (this is vasoconstriction)
- You shiver to generate heat in your muscles (exercise will do the same thing, you just heat up)
- Very little sweat is produced (as sweat can cool you down)
- Hairs (on your arms, for example) stand on end (perpendicular to your skin) to trap a layer of air which will act as an insulator to keep you warm

When you are too hot (and need to cool down)
- Blood vessels near the surface of the skin dilate (widen) so that more blood can flow near the surface, allowing for more heat to radiate into the surroundings (this is vasodilation)
- You produce lots of sweat as, when it evaporates, it transfers heat from your skin to your surroundings (this cools you down)
- Your hairs lie flat to avoid any insulating layers of air being trapped