- Epidermis (skin)
Optical coherence tomographytomogram 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 epitheliumwith an underlying basal lamina.
The epidermis is avascular (contains no
blood vessels) and is nourished by diffusionfrom 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 insoluble in fat and against those which are insoluble in water. cite journal |author=Benson, Heather A. E. |title=Transdermal drug delivery: penetration enhancement techniques. |url= http://www.ncbi.nlm.nih.gov/pubmed/16305405 |journal=Curr Drug Deliv |volume=2 |issue=1 |pages=23-33 |year=2005 |pmid=16305405 |issn=]
To overcome this barrier is a challenge for the development of transdermally delivered drugs (like nicotine patches, topically applied pain relief).
Epidermis is divided into the following 5 sublayers or strata, listed from the superficial to deep:
Stratum lucidum(not present in thin skin, only thick, hairless skin of palms & soles)
Stratum germinativum(also called "stratum basale") 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)
* - "Integument: thick skin"
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