Page 272 - 20dynamics of cancer

STEM CELLS: TISSUE RENEWAL 257

7)

''

+'

04

11

Figure 12.4 The morphology of normal colon tissue. Labels show surface ep-
ithelium (SE), colon crypts (CC), goblet cells (GC), lamina propria (LP), and mus-
cularis mucosa (MM). The crypts open to the surface epithelium—in this cross
section, some of the crypts appear partially or below the surface. From Kinzler
and Vogelstein (2002), original published in Clara et al. (1974).

2000). Renewal occurs by a flow of cells from numerous invaginations—
crypts—throughout the intestinal surface (Figure 12.4). Cells flow from
the base of each long, narrow crypt to the surface.
The small intestine of the mouse has about 15 cell layers from the ep-
ithelial surface to the base of the crypt (Figure 12.5). In the small intes-
tine, stem cells reside around the fourth cell position from the bottom.
Those stem cells produce daughters that flow either down to the lowest
layers, where they differentiate into Paneth cells, or upward where the
daughter cells continue to divide and differentiate into the functional
goblet cells and enterocytes of the intestinal epithelium.