The Skin 2014 WebMD, llc. All rights reserved. Prev

Identifiers

MeSH	D012867
TA98	A16.0.00.002
TA2	7041
Anatomical terminology [edit on Wikidata]

(See also: Rotating image)
Optical coherence tomogram of fingertip, depicting stratum corneum (~500 µm thick) with stratum disjunctum on top and stratum lucidum (connection to stratum spinosum) in the middle. At the bottom superficial parts of the dermis are visible. Ducts of sweat glands are visible.
Mammalian skin is composed of two primary layers:

• 
  The epidermis, which provides waterproofing and serves as a barrier to infection.
  
• 
  The dermis, which serves as a location for the appendages of skin.
  

Epidermis[edit]

Main article: Epidermis
The epidermis is composed of the outermost layers of the skin. It forms 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,^[12] composed of proliferating basal and differentiated suprabasal keratinocytes.
Keratinocytes are the major cells, constituting 95% of the epidermis,^[12] while Merkel cells, melanocytes and Langerhans cells are also present. The epidermis can be further subdivided into the following strata or layers (beginning with the outermost layer):^[13]

• 
  Stratum corneum
  
• 
  Stratum lucidum (only in palms and soles)
  
• 
  Stratum granulosum
  
• 
  Stratum spinosum
  
• 
  Stratum basale (also called the stratum germinativum)
  

Keratinocytes in the stratum basale proliferate through mitosis and the daughter cells move up the strata changing shape and composition as they undergo multiple stages of cell differentiation to eventually become anucleated. During that process, keratinocytes will become highly organized, forming cellular junctions (desmosomes) between each other and secreting keratin proteins and lipids which contribute to the formation of an extracellular matrix and provide mechanical strength to the skin.^[14] Keratinocytes from the stratum corneum are eventually shed from the surface (desquamation).
The epidermis contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis.