Epithelial tissue is characterized by closely packed cells with minimal extracellular matrix, forming continuous sheets that cover body surfaces and line cavities and organs. It exhibits polarity, with distinct apical and basal surfaces, and is anchored to underlying connective tissue by a basement membrane. Epithelial tissue functions primarily in protection, absorption, secretion, and sensation, playing a crucial role in processes such as filtration and gas exchange. Additionally, it is avascular, relying on diffusion from nearby blood vessels for nutrient and waste exchange.