Epidermal Layer (Epidermis)

• The Epidermis is the superficial layer of the skin and is most important in ensuring the barrier function of the skin.
• This layer can be thickened in chronic eczema (lichenification).
• A complete disappearance of the epidermis is called an “erosion”.
• This layer does NOT contain blood vessels and depends on the dermis for feeding it.
• The epidermis is divided into the following layers: basal layer, spinous layer (Malpighi Layer), granular layer, cornified layer. All in all this can be seen as a progressive differentiation between live non functional keratinocytes and dead functional ones. Between the Basal Layer and the surface (around 14 layers in humans), the differentiating cells are arranged in vertical columns.
• The epidermis is thickened for example in Psoriasis and is primarily involved in Seborrheic Keratosis. Under the microscope (histology) thickening of the epidermis (Basal Layer and spinous layer is called acanthosis.
• Cells in the epidermis include  keratinocytes, melanocytes, Langerhans cells

Reference: The Cell: A Very Short Introduction. Allen T. Oxford University Press