The epidermis is an outermost layer. It 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 cell. 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.
The Stratum spinosum: The cells that divides in the stratum germinativum soon begin to accumulate to many desmosomes (structures that join adjacent cells together) on their outer surface.
The Stratum granulosum: As keratinocyes (these are the basic cell of which the epidermis is composed) progressively mature they accumulate a protein keratin (this process is called keratinisation). In addition, the cells of the stratum granulosum accumulate dense basophilic keratohylin granules (Granules found in living cells of keratinizing epithelia).
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.
The Stratum corneum: This layer consists of primarily dead skin cells. As a cell accumulates keratinohylin 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 chemical within a cell which have expended their useful life) that eventually cause cell death. The dead and dying cells filled with mature keratin from the stratum corneum.
The Stratum spinosum: The cells that divides in the stratum germinativum soon begin to accumulate to many desmosomes (structures that join adjacent cells together) on their outer surface.
The Stratum granulosum: As keratinocyes (these are the basic cell of which the epidermis is composed) progressively mature they accumulate a protein keratin (this process is called keratinisation). In addition, the cells of the stratum granulosum accumulate dense basophilic keratohylin granules (Granules found in living cells of keratinizing epithelia).
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.
The Stratum corneum: This layer consists of primarily dead skin cells. As a cell accumulates keratinohylin 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 chemical within a cell which have expended their useful life) that eventually cause cell death. The dead and dying cells filled with mature keratin from the stratum corneum.
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