Epithelial tissue is a type of tissue that forms the protective outer layer of the body and lines internal organs and cavities. It consists of closely packed cells with minimal extracellular matrix, allowing for efficient absorption, secretion, and sensation. Epithelial tissue is classified into different types based on cell shape, such as squamous, cuboidal, and columnar, and the number of layers, including simple and stratified. This tissue serves several essential functions, including protection against physical damage, pathogens, and dehydration. It also plays a crucial role in processes like filtration in the kidneys and gas exchange in the lungs. Epithelial tissue is anchored to underlying connective tissue by a structure called the basement membrane.