One of the key features of epithelial tissue is its polarity. Epithelial cells have distinct apical (top) and basal (bottom) surfaces that serve different functions. The apical surface may contain microvilli or cilia to aid in absorption or movement of substances. In addition to its protective role, epithelial tissue also plays a critical role in maintaining homeostasis within the body. It forms selective barriers that regulate the passage of molecules and ions between different compartments.