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The stratum papillare creates a well-defined, wave-shaped
border to the epidermis.
1 Stratum papillare
2 Basal membrane
3 Basal cells
4 Epidermis
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Stratum
papillare and stratum reticulare
The stratum reticulare (reticular = net-like/Lat.) makes up the lower
part of the dermis and shows a continuous transition to subcutis.
The stratum papillare (papillae = protuberance/Lat.) is the upper
layer which is clearly demarcated from the epidermis by an undulated
border. The wave-like structure increases the contact area with the
epidermis, thus ensuring optimal nourishment of the deepest layer
of the epidermis - the basal cells - by way of the blood vessels running
through the papillae.
The connective tissue of the dermis
The main constituent of the dermis is the proteinous connective tissue
made up of arc-shaped, elastic fibres and undulated, nearly inelastic
collagen fibres. These are responsible for the high elasticity and
tensile strength of the dermis.
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Young collagen fibre -
glycosaminoglycan - can bind large amounts
of water and so determine the high intrinsic tension of young skin.
As the skin ages, the interweaving of the collagen fibres increases
and the water-binding capacity diminishes. The skin tends to wrinkle.
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Glycosaminoglycans (mucopolysaccharides)
bind with the proteinous connective tissue matrix to form proteoglycans.
These form a gel-like mass that can absorb and expel water like a
sponge. |
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Connective
tissue, glycosaminoglycane and water-binding capacity
The space within the dermal meshwork contains a sort of "filling"
made of long chains of sugar molecules (polysaccharides; poly = many,
sacchar = sugar/Gk.). These are known as glycosaminoglycans (also
mucopolysaccharides). With the help of fibronectins a type of "glue",
they bind to the proteinous connective tissue matrix to form proteoglycans,
which can bind water molecules. This gel-like mass functions like
a sponge. Under pressure it can expel the bound water and in a reverse
process take it up again. This process is the probable route of nourishment
for the dermis. Hyaluronic acid (hyalo = glass/Gk.) belongs to the
group of glycosaminoglycans and so contributes to the water-binding
whole. Glycosaminoglycans are subject to a continuous waxing and waning.
In contrast, the collagen fibres are only renewed when necessary,
such as when injury is sustained.
Other constituents of the dermis are various types of cells such as
fibroblasts, mast cells and other tissue cells, as well as a multitude
of blood and lymph vessels, nerve endings, hot and cold receptors
as well as tactile sensory organs. |
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