Infections with enteropathogenic E. coli , Giardia lamblia and Yersinia enterocolitica are all associated with loss of overlying glycocalyx and shortening of microvilli 8 . The mechanism by which this occurs is uncertain, but may involve shortening of central actin filaments. Associated reduction in disaccharidase activity may contribute to malabsorption 9 . It does this by creating a low intracellular sodium content and thus a sodium concentration gradient across the cell membrane. Fluid absorption in the small intestine and ascending colon is achieved by active transport of sodium.
Fluid secretion is associated with the active transport of chloride.
Absorption and secretion are regulated by four separate mechanisms - neural, hormonal, immune and through interaction with luminal bacteria. Intestinal cells have surface receptors on both basolateral and apical surfaces. The apical receptors are unique in that their purpose appears to be to provide targets for bacterial enterotoxins. The interaction of these pathogens with the intestinal mucosa is more complex than previously thought. ZO toxin appears to mimic physiological modulators of epithelial barrier function by causing cytoskeletal rearrangement.