lépiderme

Lépiderme, commonly known in English as the epidermis, is the outermost layer of the skin in vertebrates. It is avascular and relies on the underlying dermis for its blood supply. The epidermis forms a protective barrier against mechanical injury, pathogens, and water loss.

In humans, the epidermis is organized into layers. The main cellular component is keratinocytes, which originate in the basal layer (stratum basale) and migrate outward, differentiating as they progress through the stratum spinosum and stratum granulosum. In thick skin, a thin stratum lucidum lies between granulosum and corneum; in thin skin it is absent. The outermost layer is the stratum corneum, composed of dead, keratin-rich cells that are shed in a desquamation process. Other cell types include melanocytes, which synthesize pigment; Langerhans cells, involved in immune defense; and Merkel cells, associated with touch sensation. The epidermis lacks blood vessels; nutrients diffuse from the dermis. Melanin absorbs ultraviolet radiation, contributing to skin color and photoprotection.

Turnover time is about 28 days in healthy adults, with continuous regeneration. The epidermis renews itself following injury and plays a role in wound healing along with underlying connective tissue. Thickness varies across the body, from about 0.05 mm on eyelids to about 1.5 mm on the palms and soles.

Originates during embryonic development from the ectoderm and adheres to the basement membrane separating it from the dermis. The term epidermis derives from Greek roots meaning upon skin.