Epidermis
The epidermis is divided into five main layers (4
layers in some texts).
These layers are avascular but the deeper layers are nourished by the
tissue fluid from the vascular papillae. Starting from the deepest layer
of the epidermis, the stratum germinativum or germinative layer
(stratum = layer), is where the cells keep multiplying continuously
to provide the cells that are lost from the surface of the epidermis.
The cells from the germinative layer move upwards
into the layer above termed the prickle or spinous layer (stratum spinosum)
named for the bridges between the cells.
These two layers are often called the malphigian
layer. They are responsible for proliferation and initiation of the
keratinization process. (Kerat-, means hard)
Granular Layer
The next layer is the stratum granulosum or granular
layer where the cells contain granules which are involved in the formation
of soft keratin.
As the number and size of these granules increases
up the layer, the nucleii become pale and indistinct. It is in this layer
that cells of the epidermis die.
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