Enteroendocrine cells and Paneth cells are also derived from the stem cells at the base of the intestinal gland. Enteroendocrine cells appear to divide only once before differentiating. They migrate with the absorptive and goblet cells but at a slower rate. Paneth cells migrate downward and reside at the bottom of the intestinal gland. They live for approximately 4 weeks and are then replaced by differentiation of a nearby “committed” cell in the intestinal gland. Cells that are recognizable as Paneth cells no longer divide. As mentioned in the chapter on epithelial tissue (page 150) expression of the transcription factor Math1 appears to determine the fate of differentiating cells in the intestinal stem cell niche. The cells committed to the secretory lineage (i.e., they will differentiate into goblet, enteroendocrine, and Paneth cells) have increased expression of Math1. Inhibition of Math1 expression characterizes the default developmental pathway into absorptive intestinal cells (enterocytes).
The large intestine comprises the cecum with its projecting vermiform appendix, the colon, the rectum, and the anal canal. The colon is further subdivided on the basis of its anatomic location into ascending colon, transverse colon, descending colon, and sigmoid colon. The four layers characteristic of the alimentary canal are present throughout. However, several distinctive features exist at the gross level (Fig. 17.27):  Teniae coli that represent three narrowed, thickened, equally spaced bands of the outer longitudinal layer of the muscularis externa. They are primarily visible in the cecum
FIGURE 17.26 • Electron micrograph of the myenteric (Auerbach’s) plexus. The plexus is located between the two smooth muscle (SM) layers of the muscularis externa. It consists of nerve cell bodies (CB) and an extensive network of nerve fibers (N). A satellite cell (SC), also referred to as an enteric glial cell, is seen in proximity to the neuron cell bodies. These cells have structural and chemical features in common with glial cells of the CNS. BV, blood vessel. 3,800.
FIGURE 17.27 • Photograph of the large intestine. This photograph shows the outer (serosal) surface (left) and internal (mucosal) surface (right) of the transverse colon. On the outer surface, note the characteristic features of the large intestine: a distinctive smooth muscle band representing one of the three teniae coli (TC); haustra coli (HC), the sacculations of the colon located between the teniae; and omental appendices (OA), small peritoneal projections filled with fat. The smooth mucosal surface shows semilunar folds (arrows) formed in response to contractions of the muscularis externa. Compare the mucosal surface as shown here with that of the small intestine (Fig. 17.17).
and colon and they are absent in the rectum, anal canal, and vermiform appendix. Haustra coli that are visible sacculations between the teniae coli on the external surface of the cecum and colon.  Omental appendices that are small fatty projections of the serosa, observed on the outer surface of the colon.
The mucosa of the large intestine has a “smooth” surface; neither plicae circulares nor villi are present. It contains numerous straight tubular intestinal glands (crypts of Lieberkn) that extend through the full thickness of the mucosa (Fig. 17.28a). The glands consist of simple columnar epithelium, as does the intestinal surface from which they invaginate. Examination of the luminal surface of the large intestine at the microscopic level reveals the openings of the glands, which are arranged in an orderly pattern (Fig. 17.28b).
The principal functions of the large intestine are reabsorption of electrolytes and water and elimination of undigested food and waste.