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. Optical coherence tomography (OCT is an optical signal acquisition and processing method allowing extremely high-quality micrometre-resolution three-dimensional images from within optical At the bottom superficial parts of the dermis. Sweatducts are clearly visible.

Epidermis is the outermost layer of the skin. The skin is the outer covering of living tissue of an animal (or plant It forms the waterproof, protective wrap over the body's surface and is made up of stratified squamous epithelium with an underlying basal lamina. In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body The basal lamina is a layer of extracellular matrix on which Epithelium sits and which is secreted by the epithelial cells

Components

The epidermis is avascular (contains no blood vessels) and is nourished by diffusion from the dermis. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement The dermis is a layer of Skin beneath the epidermis that consists of Connective tissue, and cushions the body from stress and strain The main type or the four principal types of cells which make up the epidermis are keratinocytes, melanocytes, Langerhans cells and Merkels cells. The keratinocyte is the major cell type of the epidermis, making up about 90% of epidermal cells Melanocytes are cells located in the bottom layer (the Stratum basale) of the skin's epidermis and in the middle layer of the eye (the Uvea) Not to be confused with the Beta cells making up the Islets of Langerhans. Merkel cells are large oval cells found in the skin of vertebrates 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).

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 stratum corneum ("horny layer" is the outermost layer of the epidermis (the outermost layer of the Skin) For the layer of the Hippocampus, see Stratum lucidum of hippocampus. In Microscopic views of Skin, the stratum granulosum layer of the epidermis lies between the Stratum spinosum, below and the Stratum lucidum In the Skin, the stratum spinosum is a multi-layered arrangement of cuboidal cells that sits beneath the Stratum granulosum. Stratum germinativum (also stratum basale or basal cell layer) is the layer of Keratinocytes that lies at the base of the epidermis immediately 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)

Additional images

Section of epidermis. A mnemonic device (nəˈmɒnɪk is a Memory aid Commonly met mnemonics are often verbal something such as a very short poem or a special word used to help a person remember	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.

External links

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