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→Epidermis
*'''Stratum Corneum'''
*'''Stratum Corneum'''
The outer layer, ''stratum corneum'', consists of anucleate, thin cells filled with keratin filaments and proteins that form a cell envelope resistant to solvents and enzymes; there is also a permeability barrier to water and ions. The cells of the stratum corneum are embedded in a lipid-rich matrix which helps to hold the cells together, while the desmosomes that were present in lower layers have disappeared. For the stratum corneum to maintain a constant thickness, there is a constant turnover of exfoliated corneocytes, being replaced by new corneocytes. Enzymes in the lamellar bodies from the '''stratum granulosum''' help to break down the intercellular lipid 'glue' that holds the cells in place and there is also some degradation of desmosomes.
The outer layer, ''stratum corneum'', consists of anucleate, thin cells filled with keratin filaments and proteins that form a cell envelope resistant to solvents and enzymes; there is also a permeability barrier to water and ions. The cells of the stratum corneum are embedded in a lipid-rich matrix which helps to hold the cells together, while the desmosomes that were present in lower layers have disappeared. For the stratum corneum to maintain a constant thickness, there is a constant turnover of exfoliated corneocytes, being replaced by new corneocytes. Enzymes in the lamellar bodies from the '''stratum granulosum''' help to break down the intercellular lipid 'glue' that holds the cells in place and there is also some degradation of desmosomes.
====Cells of the Epidermis====
*'''Langerhans' cells'''
These are dentritic cells derived from bone marrow. They act as ''antigen presenting cells'' in the epidermis as part of the mononuclear phagocyte immune system. Langerhans' cells express MHC I and II molecules and immunoglubulin Fc receptors and are a key feature of '''delayed hypersensitivity responses.'''
===Dermis===
===Dermis===