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The
skin is made up of three successive levels
from the surface to in-depth: the
epidermis,
the
dermis,
and
the
hypodermis.
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is covered by a mixture of sweat and
sebum, the hydro-lipidic film, the first
protective barrier against exterior
aggressions, which limits the development
of bacteria through its acidity. This
fine emulsion also maintains cutaneous
moisturisation and gives the skin its
velvety look.
The
epidermis
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 The
outermost covering, the epidermis, is
the first protective barrier the organism
has. It is formed by many layers of
cells which are perfectly stratified
and contain no blood vessels. The superficial
layer, the corneal layer, is made of
keratinised cells, which are constantly
eliminated through exfoliation. These
cells have gone through a specific growth
process and have lost their nuclei and
become flat to form the superimposed
slats which scale. The corneal layer
varies in thickness according to the
area of the body, the thickest part
covering the palms of the hands and
soles ofthe feet act against friction
and constraints. However, the skin covering
the mucous membrane does not contain
keratin and is therefore without a corneal
layer. The deepest layer of the epidermis,
made up of germinal cells, ensures the
continuous renewal of the corneal layer
after cellular growth. The epidermis
takes four to six weeks to be completely
renewed. In the deeper part of the epidermis,
we can also find another type of specialized
cells called melanocytes that govern
skin colour through the production of
melanin. This pigment is found in greater
quantities in dark-skinned people than
in fair-skinned people.
The
dermis
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 The
dermis is the skin's supporting tissue.
Its specialized cells, called fibroblasts,
are in charge of the production of collagen
and elastin fibres. Collagen fibres
ensure maintenance and resistance of
the tissues by forming a densely organized
weft-like network. Finer elastin gives
the skin its suppleness and elasticity.
They decrease in number during the ageing
process and disappear completely after
the age of 45. These fibres are swimming
in a gel, rich in hyaluronic acid, which
plays a part in skin moisturisation,
locking water into molecules. The dermis
also contains blood vessels, which carry
out the role of feeding the above epidermis
and also participate in thermal regulation.
The dermis is also particularly rich
in nerve endings, which are specifically
sensitive to touch, to pain, and to
temperature, making the skin a sensorial
organ.
The
hypodermis
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 The
hypodermis is the organism's adipose
mattress giving the figure a more or
less harmonious outline. It is the most
important reservoir the body has, working
through the stocking and liberation
of fatty acids. These fatty cells, the
adipose, are the voluminous cells whose
nuclei have been flattened and pushed
to the side by a drop of lipids. Lipocytes
are distributed differently depending
on sex: for a woman they predominate
in the buttocks and thigh area, whereas,
for a man, they are to be found in the
abdominal region. In the hypodermis,
we find sweat glands as well as body
hair follicles, to which the sebaceous
glands are annexed.
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