Normal colonic epithelium consists of tubular structures called crypts or glands that are arranged in parallel and embedded in a loose connective tissue called lamina propria (Fig. 1 A–E). The lamina propria is separated from submucosa by a thin delicate layer of smooth muscle called muscularis mucosa. The covering epithelium consists of different types of cells, namely, goblet cells, columnar cells, endocrine cells, and undifferentiated stem cells. The stem cells are believed to be the source of other cell types in the crypts. The proliferative zone of the crypts is located at the base, and scattered mitotic figures are restricted to the lower third or half of the crypts. As the epithelial cells ascend from the base of the crypts to the surface, the cells undergo maturation or differentiation revealed morphologically by an increase in number of goblet cells, increase of cytoplasm, and decrease of the nuclear to cytoplasm ratio. All cells show proper polarity, namely, their nuclei are located at the base (bottom) of the cells.