Alterations in Intestinal Structure Associated with Microorganisms
The intestinal mucosa, by virtue of its villous structure, presents an extensive area of contact with the intestinal lumen. Intestinal crypts contain undifferentiated cells, Paneth cells, enteroendocrine cells, and is the site of intestinal epithelial cell renewal. The apical surface of intestinal absorptive cells is a highly specialized area which has distinct and unique properties of structure and function. Adjacent intestinal epithelial cells are attached by a characteristic junctional complex. Morphological alterations in the microvillus border of intestinal epithelial cells may be produced by a variety of microorganisms. Some of these alterations are clearly the morphological representation of adherence. The example of an organism that attaches directly to epithelial cells is that of a segmented filamentous bacterium commonly found in the rat ileum. The human intestine is often parasitized by the protozoan, Giardia lamblia. These organisms may occasionally result in extensive injury to the intestinal mucosa, the crypt cells being particularly susceptible to injury.