Answer: epithelium
Explanation: epithelial tissues are widespread throughout the body forming the covering of all body surfaces, body cavities, hollow organs and are also major tissues in glands performing various functions from secretion to protection, absorption, excretion, diffusion, sensory reception etc. This differentiation allows the cells of the epithelium to perform its function.
By definition, epithelial cells are membranous tissue composed of one or more layers of cells forming the covering of most internal- (lining of vessels and small cavities) and external surfaces (skin) of the body and its organs.
