<P> A perforated ulcer is one that has eroded through the layers of the gastrointestinal tract . </P> <P> Invasion of tumours through the layers of the gastrointestinal wall is used in staging of tumour spread . This is associated with prognosis . </P> <P> The normal thickness of the small intestinal wall is 3 - 5 mm, and 1 - 5 mm in the large intestine . Focal, irregular and asymmetrical gastrointestinal wall thickening suggests a malignancy . Segmental or diffuse gastrointestinal wall thickening is most often due to ischemic, inflammatory or infectious disease . </P> <Ul> <Li> <P> General organisation of GI tract </P> </Li> <Li> <P> The wall of the stomach . </P> </Li> <Li> </Li> </Ul>

The internal lining of the gastrointestinal tract is the