epithelium

Epithelium is a type of tissue composed of closely packed cells that form the covering or lining of surfaces and cavities in the body. It serves as a protective barrier, helps regulate permeability, and can also be involved in absorbing nutrients or secreting substances. Epithelium lines organs such as the skin, mouth, intestines, and respiratory pathways. Its structure varies from flat and thin to thick and glandular, depending on its specific function. Overall, epithelium plays a vital role in protecting internal environments and facilitating essential biological processes.