Stratum (Integumentary System); stratum basale, spinosum, granulosum, lucidum and corneum

Integumentary System

The epidermis of thick skin consists of five layers of cells (keratinocytes): stratum basale (proliferative layer), stratum spinosum (characterized by tonofibrils and associated desmosomes), stratum granulosum (characterized by keratohyalin granules), stratum lucidum (a translucent layer not obvious in thin skin), and stratum corneum (characterized by dead and dying cells with compacted keratin). Specialized structures of the skin include hair follicles (found only in thin skin), nails, and sweat glands and ducts.
The epidermis of thick skin consists of five layers of cells (keratinocytes): stratum basale (proliferative layer), stratum spinosum (characterized by tonofibrils and associated desmosomes), stratum granulosum (characterized by keratohyalin granules), stratum lucidum (a translucent layer not obvious in thin skin), and stratum corneum (characterized by dead and dying cells with compacted keratin). Specialized structures of the skin include hair follicles (found only in thin skin), nails, and sweat glands and ducts. 

Nonkeratinocyte epidermal cells include melanocytes (derived from neural crest), Langerhans cells (antigen-presenting cells derived from monocytes), and Merkel cells (sensory mechanoreceptors). Various sensory receptors and extensive capillary networks are found in the underlying dermis.

There are skin diseases with a cell biological etiology. Psoriasis is a disease characterized by dermal and epidermal infiltration of inflammatory cells. Those cells release cytokines, which cause hyperplasia of the epidermis. Proliferation occurs throughout the epidermis and is no longer restricted to the basal layer and there is a thickening of the stratum corneum with nucleated keratinocytes present. 

Pemphigus is an autoimmune disease in which autoantibodies are produced to the desmogleins, members of the cadherin family. The desmosomes break apart resulting in blistering of the skin. The basal layer remains intact and attached to the basal lamina because the hemidesmosomes do not contain cadherins. In contrast, bullous pemphigoid is a disease in which the antigen recognized by the autoantibodies is the BP (bullous pemphigoid) antigen involved in the linkage of the basal layer to the basal lamina. Bullous pemphigoid is also a blistering disease, but the blistering occurs at the epidermal-dermal junction.

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