Figure 3 Region specific permeability measurements. By carefully choosing probes that have only a limited exposure to the gastrointestinal epithelium site, selective permeability determinations can be made. Sucrose is destroyed once it leaves the stomach and so sucrose permeability is a reflection of gastroduodenal disease. In a similar manner, lactulose and mannitol are destroyed in the caecum and provide information regarding the small intestinal epithelium. Finally, probes such as sucralose and Cr‐EDTA are stable throughout the gut. They provide preferential information regarding the colonic epithelium as they spend most of a 24 hour exposure period in that organ.