The skin is the largest organ of the body and it constitutes a barrier between external environment pathogens and host’s tissues. It protects underlying muscles, organs and bones and it produces peptides with natural antibiotic function such as defensins. The skin consists of three major layers epidermis, dermis and hypodermis. Skin performs the following functions:
An anatomical barrier between the internal and external environment in bodily defense. It is the first barrier for environmental antigens.
- Heat regulation:
Dilated blood vessels increase perfusion and heat loss while constricted vessels greatly reduce cutaneous blood flow and conserve heat.
Contains a variety of nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury.
- Aesthetics and communication:
Others see our skin and can assess our mood, physical state and attractiveness.
- Control of evaporation:
The skin provides a relatively dry and impermeable barrier to fluid loss. Loss of this function contributes to the massive fluid loss in burns.
- Storage and synthesis:
The skin also acts as a storage center for lipids and water, as well as a means of synthesis of vitamin D by action of UV-light on certain parts of the skin.
Oxygen, nitrogen and CO2 can diffuse into the epidermis in small amounts. In addition, medicine can be administered through the skin, by ointment or by means of adhesive patch, such as the nicotine patch.
Sweat contains urea, however is at lower concentration than in the urine, hence excretion by sweating is at most a secondary function to temperature regulation.