Structure, Function and Care of Human Skin
By Danny Siegenthaler • February 17th, 2006 • 55672 Views
The human skin consists of two major structures. These skin structures are the Epidermis and Dermis.
The Epidermis is further subdivided into 5 Layers (from deepest to most superficial layer):
* Stratum basale
* Stratum spinosum
* Stratum granulosum
* Stratum lucidum
* Stratum corneum
The Stratum basale (also called Stratum germinativum): This is the deepest layer of the epidermis and it is here that new cells are generated for the renewal of the epidermal layers of the skin. A process of cell division referred to as mitotic division is responsible for the generation of the new epidermal skin cells. After the mitotic division (cell division leading to the formation of a new cell) a newly formed cell will undergo a progressive maturation called keratinisation as it migrates to the surface of the skin (1).
The Stratum spinosum: The cells that divide in the stratum germinativum soon begin to accumulate many desmosomes (structures that join adjacent cells together) on their outer surface (1).
The Stratum granulosum: As keratinocyes (these are the basic cell of which the epidermis is composed) progressively mature they accumulate a protein called keratin (this process is called keratinisation). In addition, the cells of the stratum granulosum accumulate dense basophilic keratohyalin granules (Granules found in living cells of keratinizing epithelia) (1).
The Stratum lucidum: This is the second layer of the epidermis and varies in thickness throughout the body depending mainly on frictional forces and is thickest on the palms of the hands and soles of the feet (1).
The Stratum corneum: This layer consists of primarily dead skin cells. As a cell accumulates keratinohyalin granules, it is thought that rupture of lysosomal membranes (membrane covering lysosomal enzymes) release lysosomal enzymes (Lysosomal enzymes are those enzymes which are responsible for breaking down complex chemicals within a cell which have expended their useful life) that eventually cause cell death (5). The dead and dying cells filled with mature keratin form the stratum corneum .
Skin Renewal Process In the Epidermis
The epidermis is composed of stratified squamous epithelium (cells) and contains four principal types of cells. About 90% of the epidermal cells are keratinocytes (i.e.: cells with finger-like or 'horny' projections). They produce the protein keratin. Keratin helps waterproof and protect the skin and underlying tissues (2).