Basic skin Biology Dermatology

Basic skin Biology Dermatology:
Is the science that deals with skin from all its aspects, i.e normal and pathological (diseased )skin .
Embryology of the skin :
Ectoderm——* keratinocytes and skin appendages. Neuroectoderm __^melanocytes and nerves. Mesoderm ———> fibroblast .collagen and elastic fibers ,blood vessels ,muscles and fat.
Functions of the skin:
1.Mechanical function: protection against chemicals , particles .ultraviolet radiation ,antigens and microbes.
2.Percutaneous absorption :the skin acts as a two way barrier to prevent the inward or outward passage of water and electrolytes. The barrier is largely situated in the epidermis within a thin layer of innermost region of stratum coreneum.
3.Immunologies! function :mainly by Langerhans1 cells which are antigen-presenting cells and play a role in contact sensitization ,immunosurveillance against viral infections and neoplasm and the rejection of skin grafts from other individuals .other cells take part in the immunological functions are indeterminate dendritic cells and keratinocytes.
4. Sensory function : a number of sensations are perceived by the skin : touch, pressure ,warmth, cold and pain .
5.Synthesis of vitamin D: vitamin D3 is essential for skeletal development .It is synthesized in the skin by keratinocytes as a result of exposure to UV B-radiation.