The skin and temperature control

General roles of the skin

• Acts as a tough, outer layer to be able to resist mechanical damage
• Acts as a barrier to the entry of disease-causing microorganisms
• Acts as a sense organ for touch and temp. changes
• Controls the loss of heat through the body's surface

Temperature control

Sweat

• Sweat glands produce greater amounts of sweat => is secreted to the surface of the skin
• This liquid evaporates and turns into a gas => this change needs energy (aka. the latent heat of vaporisation)
• When sweat evaporates, the energy is supplied by body heat => cools the body down
• Only has a cooling action when it evaporates => in humid atmospheres, the sweat stays on the skin and doesn't evaporate

Hairs

• Lies flat against skin's surface => happens because of relaxation of muscles known as hair erector muscles
• In cold conditions => muscles contract and hairs are pulled upright 
• In warm conditions => muscles relax and hairs are left lying against skin's surface
• Trap a layer of air next to the skin, and because air is a poor conductor of heat, it acts as an insulator

Blood vessels

• There are tiny blood vessels called capillary loops in the dermis 
• Blood flows through these loops, radiating heat to the outside, and cooling the body down
• If body is too hot, small arteries leading to the capillary loops dilate => increases the blood flow to skin's surface => aka. Vasodilation