Skin physiology

The skin and external mucous membranes separate the human organism from the environment and accomplish a variety of functions. Normal functioning of the skin and its appendages is of high significance for the organism's activity as a whole.

The skin not only responds by its adaptative reactions to the different effects of the external (exogenic) environmental factors, but is also very sensitive to changes in the various body organs and systems and is often the first to signal the development of a pathological condition by different changes in its function. Consequently, though the skin is an independent organ, it at the same time is in a constant dynamic connection with the external environment and with all the organs and systems of an adult and child. The skin communicates with the organism by means of the nervous system, circulation and endocrine glands. The skin takes an active part in protein, carbohydrate, fat, water-mineral, and vitamin metabolism.

Protective (barrier) function of the skin

Many properties of the skin, subcutaneous fat, and skin appendages allow us to speak of the barrier function of the skin in a broad sense, a function which contributes to the protection of the under lying organs and tissues from the pathogenic effect of the diverse environmental factors.

The skin is resistant to mechanical effects (blows, friction, compression, etc.) because of the tightness of its epithelial covering and the presence of a large amount of resilient elastic and collagen fibres and subcutaneous fat.

The stratum corneum of the skin, being a poor conductor of heat, protects the underlying tissues from drying. The thicker the stratum corneum, the more is the skin capable of withstanding the effect of electric current. In moist skin, resistance to electric current is sharply reduced.

The skin protects the organism from the damaging effect of sun rays because it contains the pigment melanin which absorbs ultraviolet rays. That is why brunettes, who have more pigment in the skin, tolerate solar insolation better than fair-haired individuals.

The skin surface is covered with an acid (pH 5.0-6.0) water-lipid mantle, which attenuates or neutralizes the damaging effect of chemical substances and prevents penetration of micro-organisms into the skin. Chemicals occurring on damaged skin or those which are soluble in the epidermal lipoids penetrate the deeper skin layers and from there may be disseminated in the body by way of the blood and lymph vessels. The sterilizing properties of the skin are due to the bactericidal properties of sweat and sebum and the continuous desquamation of the upper layers of the stratum corneum. It is believed that the chemical composition of the sebum contributes greatly to the bactericidal properties of the skin and, therefore, degreasing of the skin with alcohol or ether as well as its cooling reduce its protective functions. Heating, in contrast, increases them.

The definite role of the skin in the control of the entry of infections into the body is also a protective function.