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in Share With Other Members Tue Dec 03, 2019 2:43 am
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The human skin consists of two major structures:



* Epidermis



* Dermis


The Epidermis


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 John Cominsky Shirt , 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).



Keratinocytes in the stratum basale of the epidermis can undergo mitosis (cell division). The formation of new cells in this basal layer gradually pushes previously formed cells upward through the stratum spinosum. As keratinocytes approach the surface of the epidermis, they accumulate intracellular keratin and secrete a waxy material into the intercellular space; these changes are visible in the stratum granulosum Kendall Sheffield Shirt , a distinctive layer which is diagnostic for a keratinized epithelium. As maturing keratinocytes seal off the intercellular spaces through which they receive nutrients, they eventually die and form the stratum corneum, a tough and relatively impermeable layer of hardened Kaleb McGary Shirt , dead cells. Eventually, as cells reach the surface, they are sloughed off. The entire epidermis above the basal layer is replenished (replaced by new cells) within about two weeks (3).


Epidermal cells
There are several cells that make up the epidermis. Although the keratinocytes are by far the most common Chris Lindstrom Shirt , they are just one of the cells found in the epidermis.



Others include:
Melanocytes: The main function of melanocytes is to produce melanin, which is responsible for the colour of our skin (4).



Langerhans Cells arise from bone marrow and migrate to the epidermis. Langerhans cells interact with white blood cells called ?helper T cells? in immune responses and are easily damaged by UV radiation (2).



Merkel Cells: Merkel cells are located in the deepest layer (stratum basale) of the epidermis of hairless skin, where they are attached to keratinocytes by desmosomes. Merkel cells make contact with the flattened portion of the ending of a sensory neuron (nerve cell) Deion Sanders Shirt , called a tactile (Merkel) disc, and are thought to function in the sensation of touch (2).


Dermo-epidermal Junction


The Epidermis and Dermis are separated by the Dermo-Epithelial Junction. This junction holds the epidermis and dermis together and this is achieved by various fibers including collagen and desmosomes. This prevents the two layers becoming separated in areas of high shearing stress such as fingertips, palms of the hands and soles of the feet.


The Dermis



The Dermis consists of two sub-layers:



* The Papillary dermis and



* The Reticular dermis



The Papillary dermis (sub-epithelial layer) includes areolar connective tissue Ito Smith Jersey , dermal papillae (finger like projections that increase the surface area) and ridges that extend into the epidermis.



These nipple-shaped structures protrude into the epidermis, and many contain loops of capillaries (very small blood vessels). Dermal papillae cause ridges in the overlying epidermis. It is these ridges that leave fingerprints on objects that are handled (2).



The Reticular dermis consists of dense, irregular connective tissue containing interlacing bundles of collagen and coarse elastic fibers. Within the reticular region Deadrin Senat Jersey , bundles of collagen fibers interlace in a netlike manner. A small quantity of adipose tissue, hair follicles, nerves Isaiah Oliver Jersey , oil glands, and the ducts of sweat glands occupy spaces between the fibers. Varying thicknesses of the reticular region contribute to differences in the thickness of skin. The combination of collagen and elastic fibers in the reticular region provides the skin with If you are secretly wishing to ow. Cheap NBA Jerseys Cheap Custom MLB Jerseys Cheap MLB Jerseys Wholesale Cheap Hockey Jerseys China Cheap College Jerseys Cheap Hockey Jerseys From China Cheap Custom Jerseys Sale Cheap Custom Jerseys Free Shipping Cheap Custom Team Jerseys Cheap Custom Sports Jerseys Free Shipping

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