Epithelial tissues are layers of cells that cover surfaces and line cavities in the body. They serve various functions, including protection, absorption, secretion, and sensation. These tissues are classified based on cell shape—such as squamous, cuboidal, and columnar—and the number of layers, which can be simple (one layer) or stratified (multiple layers). Epithelial tissues are anchored to underlying tissues by a structure called the basement membrane. They are avascular, meaning they lack blood vessels, and receive nutrients through diffusion from nearby tissues. This type of tissue plays a crucial role in maintaining the body's integrity and facilitating interactions with the environment.