Function of the skin

A dynamic barrier enveloping our entire body, our skin is a complex organ that fulfils many roles that are essential for the correct functioning of the body.

Submitted on 11/12/2013

 

The vehicle of our sensations


The skin is first and foremost an organ of touch. Essential to our survival, this sense warns us against the harmful elements of our environment and is used to establish emotional contact with other people.

Thanks to the many receptors and sensory corpuscles it contains our skin enables us to experience and analyse external stimuli: pressure, touch, vibrations, heat, pain, etc. These receptors are of different types, each specialised in a category of sensations. They collect sensory information which they then transmit to the brain via a network of nerve fibres. The information is then analysed in order to provide an appropriate response.


A barrier against aggression


The skin is also a protective barrier against the many harsh external factors of our environment:
 
  • Mechanical pressure


The elasticity of the dermis and the layer of fatty tissue of the hypodermis allow our skin to protect the body against shocks. If repeated friction is exerted on the same area of the body, the stratum corneum (outermost layer of the epidermis) thickens to absorb the pressure.
 
  • Penetration of foreign agents


Made up of corneocytes bound together by lipids, the stratum corneum is an almost impermeable layer that prevents the penetration of harmful chemical agents into the body.

In addition, it is permanently covered by the hydrolipidic film composed of sweat, water and protein that has been degraded via cornification. Thanks to its pH (between 4.5 and 5.5), the hydrolipidic film encourages "good bacteria" which thrive between the corneocytes (more than 1000 per m2) and prevent undesirable bacteria, fungi and viruses from proliferating and penetrating into the body. The balance of the hydrolipidic film is therefore essential for good skin health: if it is impaired our skin can no longer function effectively as a barrier and it becomes more susceptible to aggression and infections.

If a foreign body is able to cross the hydrolipidic film, the skin still has immunological resources to eliminate it. Firstly, when a foreign agent is detected on the surface of the skin, the keratinocytes synthesize antimicrobial peptides that have a broad antibacterial action. Then the Langerhans' Cells intervene as true sentinels of the skin that catch unwanted elements and transmit them to the T lymphocytes, killer cells that trigger their elimination. The dermis contains an additional line of defence: bacteria or viruses that may have escaped the vigilance of the Langerhans' cells are detected and eliminated by the macrophages.
 
  • UV rays


Our epidermis contains melanocytes, cells that produce a natural brown pigment, melanin, and distribute it to neighbouring keratinocytes through dendrites (cell extensions in the form of branched projections).When skin is exposed to sunlight, the melanocytes increase their production of melanin and their dendrites grow longer. The skin thus has natural double photoprotection:

           - The melanin absorbs the UV rays to prevent them from penetrating into the deeper and more vulnerable layers of the skin.
          - Drenched in melanin, the keratinocytes grow bigger and the stratum corneum thickens.

However, beyond a certain quantity of UV rays, damage to skin is inevitable. This threshold varies among individuals: fairer skin types are less resistant. 


A regulator of body temperature


Situated most often between 28 and 32°, the external temperature of our skin can vary between 20 and 40° without damage. But within our body, it must remain constant at around 37° for the body to function properly. The skin plays a fundamental role in maintaining this internal temperature constant:
 
  • In the event of heat (fever or high outside temperature), the blood vessels which supply the skin with blood dilate: more blood travels to the surface, enhancing heat loss. Meanwhile, the sweat glands secrete more sweat in order to evacuate excess heat.
  • On the contrary, when it is cold sweating diminishes and the blood vessels shrink. The epidermis thus becomes as insulating as possible to maintain the internal heat.

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