Structure of Skin
The skin is composed of two distinct layers: epidermis and dermis.
It is the superficial avascular layer of stratified squamous epithelium, It is ectodermal in origin and gives rise to the appendages of the skin, namely hair, nails, sweat glands and sebaceous glands.
Structurally the epidermis is made up of a superficial cornified zone and a deep germinative zone. The cells of the deepest layer proliferate and pass towards the surface to replace the cornified cells lost due to wear and tear. As the cells migrate superficially, they become more and more flattened and lose their nuclei to form flattened dead cells of the stratum corneum. In the germinative zone, there are cells which synthesize melanin.
Dermis or corium is the deep, vascular layer of the skin derived from mesoderm. It is made up of connective tissue mixed with blood vessels, lymphatics and nerves. The connective tissue is arranged into a superficial papillary layer and a deep reticular layer. The papillary layer forms conical, blunt projections, called dermal papillae. These papillae fit into reciprocal depressions on the undersurface of the epidermis. The reticular layer is composed chiefly of the white fibrous tissue arranged mostly in parallel bundles.
The direction of the bundles constitutes the flexor lines, also known as cleavage lines or Langer’s lines. These are longitudinal in the limbs and horizontal in the trunk and neck.
At the flexure lines the skin is firmly adherent to the underlying deep fascia. Dermis is the real skin, because when dried it makes green hide and when tanned it makes leather. Its deep surface is continuous with the superficial fascia.