Epidermis (skin)
From Wikipedia, the free encyclopedia
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.
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[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
- ^ a b James, William; Berger, Timothy; Elston, Dirk (2005) Andrews' Diseases of the Skin: Clinical Dermatology (10th ed.). Saunders. Page 2-3. ISBN 0721629210.
- ^ a b c d McGrath, J.A.; Eady, R.A.; Pope, F.M. (2004). Rook's Textbook of Dermatology (Seventh Edition). Blackwell Publishing. Pages 3.1-3.6. ISBN 9780632064298.
- ^ a b c Marks, James G; Miller, Jeffery (2006). Lookingbill and Marks' Principles of Dermatology (4th ed.). Elsevier Inc. Pg 1-7. ISBN 1-4160-3185-5.
- ^ Brannon, Heather, MD (2007) Dermatology - Epidermis @about.com http://dermatology.about.com/cs/skinanatomy/g/epidermis.htm
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