Epithelium is a type of tissue that covers the surfaces of the body, including the skin, digestive tract, respiratory tract, and other organs. It serves as a protective barrier that helps to regulate the exchange of substances between the body and the external environment. Research on epithelium focuses on understanding its structure, function, development, and response to various stimuli. This area of study is important for gaining insights into the roles of epithelial cells in health and disease, as well as for developing potential treatments for epithelial-related disorders.