epithelium

A membranous tissue composed of one or more layers of cells which forms the covering of most internal and external surfaces of the body and its organs: internally including the lining of vessels and other small cavities, and externally being the skin.countableuncountable

• the passenger's roving eyes paused for a moment as he listened inwardly to a nether itch, which he supposed to be (correctly, thank Log) only a minor irritation of the epithelium.
• The sap of this species was able to cause loss of corneal epithelium 16 h after direct exposure to the sap in a 60-year-old male.