In the human body, the cells with the strongest regenerative capacity are epithelial cells, which in turn include a variety of species, including single-layer flat epithelial cells, single-layer columnar epithelial cells, compound flat epithelial cells, migratory cells, compound ciliated columnar epithelial cells, and glandular epithelium. All epithelial cells have relatively strong regenerative ability. Generally these epithelial cells are mainly distributed on the surface of human respiratory tract, digestive tract and genitourinary tract, so the cells in these parts have the strongest regenerative ability. If a normal person has a mouth ulcer, the ulcer can generally heal in a relatively short period of time due to the strong regenerative ability of the monolayer flat epithelial cells. Likewise for the genitourinary system, the multiple flat epithelial cells also have a strong regenerative capacity and will repair as soon as possible after a breakage occurs.