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1. Stratum Germinativum (Basale)
The deepest layer of the
epithelium and attaches to the basal lamina. |
This layer contains stem cells
(basal cells) that provide a continual supply of new
keratinocytes to replace those that are lost. |
Melanocytes are found in this
layer. |
Merkel cells are also present in
skin that lacks hair (e.g. lips, palms and soles). |
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2. Stratum Spinosum
This layer is several cells thick. |
These cells form a strong
attachment to one another because they are connected to one
another by anchoring junctions (desmosomes) and these intercellular
attachment are braced by bundles of keratin filaments
called tonofilaments. |
Some cells in this layer continue
to divide after separating from the basal lamina. |
Melanocytes and Langerhans cells
are also present in this layer. |
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3. Stratum Granulosum
As the keratinocytes are pushed
toward the surface they produce the proteins keratohyalin and
keratin which accumulates in keratohyalin granules. |
The proteins in the keratohyalin
granules organize the keratin
filaments into bundles that cause the cells to become flattened. |
Insoluble proteins accumulate on
the cytoplasmic side of the cell membrane while lipids are
deposited on the other side. This makes the interlocked cells
more impermeable to water. |
As the cells enter the next
stratum the organelles disintegrate and the cells die. |
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4. Stratum Lucidum
This layer is only seen in the thick
skin of the palm and the sole and is considered
a subdivision of the stratum corneum by many histologists. |
In the light microscope, it often
has a
refractile appearance and may not pick up stain. Hence, it
appears clear or
lucid. |
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5. Stratum Corneum
This is the most superficial layer
in thin and thick skin and consists of layers of dead,
flattened and tightly interlocked cells. |
The keratinized cells of this
layer forms a dry environment unsuitable for microorganisms. |
This layer also forms a
water-resistant layer that allows some water to be lost by
insensible perspiration.
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