The epidermis is the outer layer of the skin,^[1] composed of terminally differentiated stratified squamous epithelium,^[2] acting as the body's major barrier against an inhospitable environment.^[3] It is the thinnest on the eyelids at .05 mm and the thickest on the palms and soles at 1.5 mm.^[4]It is ectodermal in origin.

Contents 1 Cellular components 2 Layers 3 Cellular kinetics 4 Additional images 5 References

[edit] Cellular components

The epidermis is avascular, nourished by diffusion from the dermis, and composed of four types of cells, i.e. keratinocytes, melanocytes, Langerhans cells, and the Merkel cells.^[1] Keratinocytes are the major constituent, constituting 95% of the epidermis.^[2]

[edit] Layers

The epidermis is composed of 4-5 layers depending on the region of skin being considered. Those layers in descending order are the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale.^[3] The term Malpighian layer refers to both the basal and spinosum layers.^[2]

[edit] Cellular kinetics

The stratified squamous epithelium is maintained by cell division within the basal layer. Differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where anucleate corneal cells are continually shed from the surface (desquamation). In normal skin, the rate of production equals the rate of loss,^[2] taking about two weeks for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional four weeks to cross the stratum corneum.^[3]

[edit] Additional images

Epidermis and dermis of human skin

Section of epidermis

Optical coherence tomography of fingertip

Cross-section of all skin layers

[edit] References

v • d • e Integumentary system (TA A16, GA 10.1062) Skin Epidermis Stratum corneum · Stratum lucidum · Stratum granulosum · Stratum spinosum · Stratum germinativum (basale) Basement membrane zone Basal keratinocyte · Lamina lucida · Lamina densa Dermis Papillary · Reticular Subcutaneous tissue Panniculus adiposus · Panniculus carnosus · Stratum membranosum · Loose connective tissue · Superficial fascia Adnexa Glands Sweat glands: Apocrine · Eccrine Sebaceous Hair Outer root sheath Inner root sheath Shaft Cuticle · Cortex · Medulla · Bulb with matrix cells · Hair papilla Muscle Arrector pili Nail Matrix · Lunula · Nail plate · Eponychium · Paronychium · Hyponychium Other Skin flora integument, SF, LCT navs: anat/physio, noncongen/congen/neoplasia, symptoms+signs/eponymous, proc skin appendage navs: anat, noncongen/congen/neoplasia, symptoms+signs/eponymous, proc