Epidermis

Epidermis is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface and is made up of stratified squamous epithelium with an underlying basal lamina.

Structure

The epidermis is composed of multiple layers of flattened cells that overlie a base layer (stratum basale) of columnar cells. The layers of cells develop from stem cells in the basal layer. New cells gradually push older ones upwards towards the surface of the skin, where they form a protective layer before they are shed.

Layers

The epidermis is divided into several layers where cells are formed through mitosis at the innermost layers. They move up the strata changing shape and composition as they differentiate and become filled with keratin. They eventually reach the top layer called stratum corneum and become sloughed off, or desquamated. This process is called keratinization and takes place within weeks.

The layers of epidermis include:

• Stratum corneum
• Stratum lucidum
• Stratum granulosum
• Stratum spinosum
• Stratum basale

Functions

The epidermis serves several functions: it protects against water loss, regulates the amount of water released from the body into the atmosphere through transepidermal water loss, and acts as a barrier against the external environment.

Clinical significance

Damage to the epidermis can occur in a variety of ways, including burns, skin disorders, and infections. Diseases of the epidermis include, for example, eczema, psoriasis, skin cancer, dermatitis, impetigo, and vitiligo.

See also

• Dermis
• Skin
• Human skin

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