The epidermis is composed of the outermost layers of the skin, forming a protective barrier over the body’s surface, responsible for keeping water in the body and preventing pathogens from entering, and is a stratified squamous epithelium, composed of proliferating basal and differentiated suprabasal keratinocytes.

A complex, self renewing barrier covering a large fraction of the body.

It acts as a barrier, keeping water in and preventing the invasion of micro organisms.

The basal-cell layer of keratocytes has the potential for growth and migration

Varies in thickness from .05 mm on eyelids to approximately 1.5 mm on the palms and soles.

Cellular proliferation in the epidermis is limited to the epidermal stem cells in the basal layer, the innermost cell layer.

The epidermal layer does not contain any blood vessels or nerve endings but melanocytes and basal cells are embedded in this layer. 

The basal layer contains stem cells of the epidermis as they are undifferentiated proliferating cells.

Basil stem cells differentiate as they exit the basal layer taking approximately four weeks to migrate from the basal layer to the top of the stratum corneum where they are finally shed.

Injury or inflammation to the epidermis can speed this transition process.

After cell division in the basal layer, daughter cells exit the cell cycle and migrate upward to form the spine is cell layers.

In the spinous cell layers cell junctions have added keratin proteins and strengthened cell junctions.

Cells in the granular layer, close to the surface, contain cytoplasmic granules with mainly profilagrin, and other proteins required for the formation of flattened, dead cells, squames, the outermost stratum corneum responsible for the barrier function of the skin.

The stratified cornified squamous epithelium prevents water loss via of the large surface area, and blocks entry of foreign substances from the external environment.

The top layer of the epidermis is that stratum corneum which contains keratin cells and which is barrier like and has multiple other functions besides protection.

The stratum corneum is elastic, semi permeable,and pliable.

Contains keratinocytes which synthesize protein keratin, which has a protective role.

The dermis contains melanocytes, keratinocytes, Langerhans cells, and Merkel cells.

Merkel cells are in high concentrations in the fingertips and lip areas which results in higher tactile resolution and sensitivity than other areas of the skin.

Mixed in the basal cell layer of the epidermis are melanocytes which have branched extensions that reach 30-40 keratinocytes and that deliver melanosomes that are phagocytized by the keratinocytes and placed as a protective layer above the nucleus.

Melanocytes produce melanin a brown-black pigment and found mostly in the epidermis.

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