ABSTRACT
The gastrointestinal (GI) mucosa forms a barrier between the body and a lumenal environment, which not only contains nutrients, but also is laden with potentially hostile microorganisms and toxins. The challenge is to allow efficient transport of nutrients across the epithelium while rigorously excluding passage of harmful molecules and organisms. The GI epithelium is populated by a variety of functionally mature cells derived from proliferation of stem cells. Many of these cells, including mucous cells in the stomach and absorptive cells in the small intestine, show rapid turnover rates, and maintenance of epithelial integrity thus requires a precise balance between cell proliferation and cell death. Normal proliferation of gastric and intestinal epithelial cells, as well as proliferation in response to injury such as ulceration, is known to be affected by a large number of endocrine and paracrine factors.
