<P> Skin performs the following functions: </P> <Ol> <Li> Protection: an anatomical barrier from pathogens and damage between the internal and external environment in bodily defense . (See Skin absorption .) Langerhans cells in the skin are part of the adaptive immune system . </Li> <Li> Sensation: contains a variety of nerve endings that jump to heat and cold, touch, pressure, vibration, and tissue injury (see somatosensory system and haptic perception). </Li> <Li> Thermoregulation: eccrine (sweat) glands and dilated blood vessels (increased superficial perfusion) aid heat loss, while constricted vessels greatly reduce cutaneous blood flow and conserve heat . Erector pili muscles in mammals adjust the angle of hair shafts to change the degree of insulation provided by hair or fur . </Li> <Li> Control of evaporation: the skin provides a relatively dry and semi-impermeable barrier to reduce fluid loss . </Li> <Li> Storage and synthesis: acts as a storage center for lipids and water </Li> <Li> Absorption through the skin: Oxygen, nitrogen and carbon dioxide can diffuse into the epidermis in small amounts; some animals use their skin as their sole respiration organ (in humans, the cells comprising the outermost 0.25--0.40 mm of the skin are "almost exclusively supplied by external oxygen", although the "contribution to total respiration is negligible") Some medications are absorbed through the skin . </Li> <Li> Water resistance: The skin acts as a water resistant barrier so essential nutrients aren't washed out of the body . The nutrients and oils that help hydrate the skin are covered by the most outer skin layer, the epidermis . This is helped in part by the sebaceous glands that release sebum, an oily liquid . Water itself will not cause the elimination of oils on the skin, because the oils residing in our dermis flow and would be affected by water without the epidermis . </Li> <Li> Camouflage, whether the skin is naked or covered in fur, scales, or feathers, skin structures provide protective coloration and patterns that help to conceal animals from predators or prey . </Li> </Ol> <Li> Protection: an anatomical barrier from pathogens and damage between the internal and external environment in bodily defense . (See Skin absorption .) Langerhans cells in the skin are part of the adaptive immune system . </Li> <Li> Sensation: contains a variety of nerve endings that jump to heat and cold, touch, pressure, vibration, and tissue injury (see somatosensory system and haptic perception). </Li>

Cross section of the skin and its functions