Epithelial cells are a type of cell that make up the epithelium, which is the thin layer of tissue that covers the surface of organs, glands, and other structures in the body. Epithelial cells are found in many different organs and tissues throughout the body, including the skin, respiratory tract, gastrointestinal tract, and urinary tract.

Epithelial cells have a number of important functions, including providing a barrier between the internal and external environments of the body, absorbing nutrients and other substances, and secreting mucus and other fluids. Epithelial cells are also involved in sensory functions, such as detecting changes in temperature or pressure, and in the immune response, by acting as a physical barrier to pathogens and producing antimicrobial compounds.

Epithelial cells are polarized, meaning they have distinct structural and functional properties at their apical (upper) and basolateral (lower) surfaces. The apical surface faces the external environment or lumen of a hollow structure, while the basolateral surface faces the underlying connective tissue or basement membrane. This polarity allows epithelial cells to perform specialized functions, such as transporting ions and molecules across membranes, and to maintain tissue structure and organization.

Epithelial cells can be obtained from a variety of sources, including biopsy samples, cell culture, and stem cell differentiation. They are commonly used in research to study cell biology, tissue development, and disease processes, and in drug discovery and toxicology studies.