The Function of Skin

The most obvious function of the skin is as a protective barrier against harmful agents in the outside environment. The dense, thick layers of cells help to prevent physical and chemical damage, while preventing microscopic pathogens from entering the body. The cells of the immune system present in the skin, as well as acidic and microbicidal secretions (sweat, oil, etc.) from subcutaneous glands also prevent the entry of potentially harmful invaders. Microbes are unable to colonize the skin due to the constant shedding of the external layer. The damaging effects of the sun's UV radiation on DNA are reduced due to the pigment melanin, present in the cells of the epidermis [1].

The skin also provides a barrier that prevents the loss of components out of the body. The stratum corneum forms an impermeable layer, preventing the evaporation of water and therefore dehydration [1].

The skin also plays a role in heat regulation. An increase in heat production will stimulate the excretion of sweat, which cools the body surface, from merocrine sweat glands which span the layers of the skin (see Figure 4). Heat leaves the body via conduction, passing from dilated blood vessels, through the skin, and into the external environment. A decrease in circulation under the skin will conserve heat [5].

Fig. 4: A section of sweat glands in the skin.

(from Junqueira and Carneiro, 2005)

The epidermal layer is rich in free nerve endings, as are the dermal papillae (extensions of the dermis into the epidermis). These nerve endings (Figure 5) provide the body with critical information from the environment. Pain, temperature, pressure, and tactile stimuli are received at the skin's surface, sending information to the nervous systems so as to elicit an appropriate response [1].

Fig. 5: Four types of nerve endings found in the skin.

(from Junquiera and Carneiro, 2005)