Changes

*'''Stratum Corneum'''

*'''Stratum Corneum'''

The outer layer, ''stratum corneum'', consists of 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.

The outer layer, ''stratum corneum'', consists of 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.

 

Deep to the stratum corneum, lies the stratum granulosum.  Granular cells are thin, flattened keratinocytes with variably prominent keratohyaline granules.  At its outer surface, the stratum granulosum secretes oragnelles called '''lamellar bodies''', which are composed of lipid and enzymes which fuse with the plasma membrane and help to form the water concentration gradient that leads to transepidermal water loss.

===Dermis===

===Dermis===