Intestinal stem cells and the development of colorectal neoplasia

The mammalian intestinal epithelium is a rapidly renewing tissue in which tissue homeostasis is regulated by a balance between cell proliferation, differentiation, and apoptosis. Over the last three decades, investigators have described the structure and cell kinetics of the functional unit—the intestinal crypt (known as the crypt of Lieberku¨hn in the small intestine)—and evidence has accumulated to support the concept that there are principally four differentiated intestinal cell types (enterocytes, mucosecreting or goblet cells, enteroendocrine cells, and Paneth cells in the small intestine), derived from a common pluripotent progenitor cell, the intestinal stem cell, located at or just above the bottom of the intestinal crypt. The first half of this chapter will review the evidence behind these prevailing concepts. Until recently, chapters on intestinal stem cells concluded.