1.General feature: (1) contain more cells and less extracellular ground substance (2) Polarisaton: ---free outer surface: face air or other things ---basal surface: face underlying CT, havebasement membrane (3) Avascularity,but innervation: ---no blood vessels ---rich in nerve terminals
---skin is the largest organ of the body, it constitutes about 16% of body weight ---its total surface area is about 1.2-2.2 m2 ---function: protection, sensory reception, excretion and thermoregulation
① Lymphocyte: a. T-lymphocytes: cytotoxic T cell: Tc C- kill the tumor cell, virus infective cell and foreign cell helper T cell: Th C- promotes activity of BLC and Tc C suppressor T cell: Ts C –regulate the function of BLC and TC