Figure 1. Sequence of events in the pathogenesis of intestinal radiation injury. In addition to breakdown of the epithelial barrier, the development of early and delayed manifestations is influenced by a large number of inflammatory mediators, cytokines and growth factors(right), many of which are released by cells of the immune system. In the special case of the bowel, injury is also significantly influenced by the contents of the intestinal lumen (left). These contents are normally separated from the intestinal stromal tissues by the mucosal barrier. After irradiation, breakdown of the mucosal barrier allows intraluminal factors to gain access to and affect the stromal tissue and thus exacerbate manifestations of intestinal injury.