The function of the skin
Each of the structures which comprise the skin has one or more functions, many of
which play a vital role in maintaining good health. Those which may be affected in
acne, eczema or psoriasis are also described in a little more detail.
A primary purpose of the skin is to provide a flexible, protective shield between us
and the outside world. This is made possible by the layers of dead, flattened
epithelial cells which prevent micro-organisms and chemicals from entering the body,
and by the waterproofing effect of the keratin, fats and oils. These protective benefits
would not last long, however, if skin cells were not replaced. This happens by a
process of continuous cell division in the basal layer, nutrients being provided by the
blood vessels in the papillary layer. As the cells move towards the outer surface, they
lose their nuclei, gradually become keratinised, and die.
Linked with cell division is the process of wound healing. This involves the inward
migration of cells such as fibroblasts and white blood cells, the release of special
chemicals called growth factors that stimulate the repair process, and increased cell
division of the epidermis to provide a new, intact surface layer. Redness and swelling
around a wound indicates that the blood vessels are enlarged and ‘leaky’ – a
reflection of inflammation and an immune response which contribute to the removal
of dead and damaged tissue.
Temperature regulation is also an important activity of the skin. The large amounts of
liquid lost during perspiration evaporate from the surface and cool it. Also, blood
vessels open up to dissipate heat when you are overheated – hence the pink flush
when you are warm – and contract when the body needs to conserve heat. Sweat
also contains waste materials such as urea and up to 1 gramme of waste nitrogen
may be lost through the skin every hour.
Skin also has a protective role in screening out potentially harmful ultraviolet (UV)
rays from the sun by manufacturing melanin pigments. However, UV is also involved
in chemical reactions leading to the synthesis of vitamin D3 – vital for normal growth
of teeth and bones and for the absorption of calcium from food. Blood and lymphatic
vessels are more numerous in the hypodermis than in the dermis, showing that it
plays a key role in defence against the penetration of foreign materials or pathogens.
Its other functions are largely storage (fats), cushioning and attachment.