<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> The gastrointestinal wall surrounding the lumen of the gastrointestinal tract is made up of four layers of specialised tissue--from the lumen outwards: </P> <Ul> <Li> Mucosa </Li> <Li> Submucosa </Li> <Li> Muscular layer </Li> <Li> Serosa (if the tissue is intraperitoneal) / Adventitia (if the tissue is retroperitoneal)--these last two tissue types differ slightly in form and function according to the part of the gastrointestinal tract they belong to (see the section below for more detail) </Li> </Ul> <Li> Serosa (if the tissue is intraperitoneal) / Adventitia (if the tissue is retroperitoneal)--these last two tissue types differ slightly in form and function according to the part of the gastrointestinal tract they belong to (see the section below for more detail) </Li>

The basic arrangement of histological layers that make up most regions of the gi tract are