Epidermis (skin)

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Cross-section of all skin layers

Optical coherence tomography tomogram of fingertip, depicting stratum corneum (~500µm thick) with stratum disjunctum on top and stratum lucidum (connection to stratum spinosum) in the middle. At the bottom superficial parts of the dermis. Sweatducts are clearly visible.

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.

[edit] Components

The epidermis is avascular (contains no blood vessels) and is nourished by diffusion from the dermis. The main type or the four principal types of cells which make up the epidermis are keratinocytes, melanocytes, Langerhans cells and Merkels cells. The outermost layer of epidermis consists of 25 to 30 layers of dead cells.

The human skin is organised in distinct layers. Cells are born in the deep layers and migrate outward, flattening as they go, to form a protective barrier of dead cells at the surface (stratum corneum). The stratum corneum is a multi-layered brick and mortar like structure. It consists of lipid bilayers with alternating hydrophilic and hydrophobic areas. This is an efficient barrier against chemicals that are unsoluble in fat and against those which are unsoluble in water.^[1] To overcome this barrier is a challenge for the development of transdermally delivered drugs (like nicotine patches, topically applied pain relief).

[edit] Sublayers

Epidermis is divided into the following 5 sublayers or strata, listed from the superficial to deep:

• Stratum corneum
• Stratum lucidum (not present in thin skin, only thick, hairless skin of palms & soles)
• Stratum granulosum
• Stratum spinosum
• Stratum germinativum (also called "stratum basale")

It is the deepest layer of the skin specifically the epidermis. The anatomical structure of it is composed of a single row of cuboidal or columnar keratinocytes.

Mnemonics used for remembering the layers of the skin (using "stratum basale" instead of "stratum germinativum"):

• "Corn Lovers Grow Several Bales" (from superficial to deep)
• "Come Lets Get Some Beers" (from superficial to deep)
• "Californians Love Girls in String Bikinis" (from superficial to deep)
• "Before Signing, Get Legal Counsel" (from deep to superficial)

[edit] Additional images

Section of epidermis.	Skin layers.	Histopathological image of dyshidrotic dermatitis, showing focal spongiotic change in the epidermis.	Schematics of internal human skin depicting its inner structure.
The distribution of the bloodvessels in the skin of the sole of the foot.	Cross section showing layers of epidermis.

[edit] External links

• Histology at BU 08422loa - "Integument: thick skin"