Schematic of intestinal structure and epithelial cell types. (a) Layers of the adult intestine. In addition to the intestinal epithelium, there are circular and smooth muscle layers and a submucosal layer. The enteric nervous system of the intestine is comprised of a submucosal and myenteric neural plexus. (b) Cell types of the intestinal epithelium shown in (a). Markers for each cell type are shown in parentheses (that is, CDX2). Paneth cells and stem cells are in the crypt and enterocytes; goblet cells and enteroendocrine cells are in the villus. Figure from Howell and Wells  with permission.