The skin and its functions - Mavi 2012

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The skin and its functions

Health Area > Dermatology

The skin performs important tasks: it protects against the outer environment, communicates with inner organs and plays a major role in social life. The skin should allow some substances to penetrate and prevent others, defend us from attacks by external agents   and ensure mechanical, thermal and chemical protection. The function of the skin as a whole consists basically in protecting the body and allowing human relations. The protective function is promoted mainly by keratin in the outermost epidermal layer, that is proteic stratum corneum. Located beneath the horny layer are the stratum granulosum, made up of flattened cells; the stratum spinosum, whose cells are polygonal-shaped and have extensions forming intercellular spaces through which the epithelial lymph flows; and, finally, the basal layer made up of cylindric cells resting on the basal membrane. From this layer cells migrate upwards to the stratum corneum through the spinosum, within the continual process of complete epidermal renewal occurring in cycles of approx. 28 days. This continual maturation process makes the skin easily attackable by external agents which may interfere with the "work of cellular DNA and RNA" requiring continual repairs. An agent attacking a cell during its reproductive stage may cause permanent damage, since it is transmitted to following cell generations.
External agents and substances (such as creams) should not hinder in any way the epidermal renewal process which must occur regularly.
As shown above, the agents which may attack the skin are either occasional, such as bacteria, viruses and chemical agents, or recurring, such as the sun’s rays. Special attention should be paid to the latter agents as recurring ones. In fact, UV rays always cause damage which the skin is able to repair only partly and through delayed-action physiological mechanisms. The cells in the epidermal layer are bound to one another by intercellular bridges, but the dermis, consisting of elastic and collagen fibers, is the one agent making the skin resistent. Obviously, elastic fibers are more numerous in young individuals, while collagen fibers increase with age. The junctional membrane separates and connects the dermis and epidermis. When the dermal fibers  lose their functionality, the epidermis is deprived of the support of underlying dermis and small, more or less deep and extensive furrows develop which we call wrinkles and are peculiar to aged skin.
The skin has a number of sensitive innervations, which are crucial to the social life of an individual. In fact, the skin is the departure and arrival points for many stimuli. There are three main types of sensations: homeomorphous sensations, such as tactile ones; homeothermal sensations; such as heat and cold; and homeochemical sensations, which depend on attacks by external substances.
With regard to the function corresponding to the first type of sensations, a sensation occurs when a stimulus produced on the skin reaches given values. The intensity of a stimulus is of major importance: it may cause pain and, as in all sense organs, habituation and adjustment. In the former case, the skin acts as an alarm and protects against dangers by means of signals reaching the central nervous system through peripheral nerves. In the latter case, adjustment enables the skin to coexist with things in close contact, such as glasses, rings or other, since it no longer perceives their presence. So, a thing we cannot bear at first, does not bother us after a certain period of time. The combination of the three major sensorial modes allows us to perceive and recognize surfaces, things and  substances. Thermal sensitivity concerns two types of receptors, those of heat and cold, which are located in different areas of the skin at different concentrations, with cold receptors being markedly higher in number.
A dermatologist is constantly called on to solve problems concerning either skin ageing due to some diseases, including diskeratosis and actinic keratosis, or physiological factors, including wrinkles and men’s seborrhoic alopecia.

 
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