About The Skin

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. We need not discuss this complex process in detail, but it 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.

PART	FUNCTION
Stratum corneum (Horny layer)	• Prevents uncontrolled loss or entry of water • Prevents entry of pathogens and most toxic chemicals when undamaged
Stratum basale (Basal layer)	• Continuous cell division to replace shed skin cells
Melanocytes	• Make melanin when exposed to ultraviolet (UV) light
Melanin	• Protects living skin cells from damage by UV in sunlight

Function of the various components of the epidermis

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.

PART	FUNCTION
Papillary layer	• Provides oxygen and sustenance to the basal layer to maintain active cell division
Hair (follicles)	• Protect sensitive body areas such as the scalp • Prevent dust and foreign bodies entering the nose and eyes • Prevent sweat entering the eyes (eyebrows and lashes) • Help with temperature control (hairs erect when shivering)
Nails	• Protection from mechanical injury • Help in picking up and gripping with fingers
Nerve receptors	• Detect external stimuli such as heat, cold, vibration, gentle touch, deep pressure and pain
Sebaceous glands	• Oily secretion (sebum) prevents skin and hair drying out
Eccrine sweat glands	• Temperature control by evaporation of secreted watery sweat
Apocrine sweat glands	• Respond to stress (including sexual activity) by producing sweat with a characteristic odour • Produce pheromones – chemicals that communicate with others to elicit a certain type of behaviour
Small arteries	• Open when warm to increase heat loss • Constrict in cold to conserve body heat • Constrict in stressful situations to shunt blood to other organs • Deliver immune cells to the skin
Fibrous network	• Collagen fibres provide strength, the thinner reticular fibres create a supportive network, while elastin fibres give elasticity
Loose connective tissue	• Connects skin to underlying muscle • Contains many white blood cells that destroy pathogens that enter through breaks in the skin
Fat layers	• Store energy in the form of fats • Act as a cushion over bony areas • Provide some insulation from cold

< Previous Page | Contents | Next Page >