Epithelial cells are a type of cell that forms the tissue lining the surfaces and cavities of organs in the body. They serve as a protective barrier and are involved in various functions, including absorption, secretion, and sensation. Epithelial tissue can be found in areas such as the skin, lungs, and digestive tract, where it plays a crucial role in maintaining the body's integrity and function. These cells are characterized by closely packed structures with minimal space between them, allowing for effective protection and selective permeability. Epithelial cells can be classified into different types based on their shape—such as squamous, cuboidal, and columnar—and the number of layers they form, which can be simple or stratified.