<P> The parts of the colon are either intraperitoneal or behind it in the retroperitoneum . Retroperitoneal organs in general do not have a complete covering of peritoneum, so they are fixed in location . Intraperitoneal organs are completely surrounded by peritoneum and are therefore mobile . Of the colon, the ascending colon, descending colon and rectum are retroperitoneal, while the cecum, appendix, transverse colon and sigmoid colon are intraperitoneal . This is important as it affects which organs can be easily accessed during surgery, such as a laparotomy . </P> <P> The average inner diameter of sections of the colon in centimeters (with ranges in parentheses) are cecum 8.7 (8.0 - 10.5), ascending colon 6.6 (6.0 - 7.0), transverse colon 5.8 (5.0 - 6.5), descending / sigmoid colon 6.3 (6.0 - 6.8) and rectum near rectal / sigmoid junction 5.7 (4.5 - 7.5). </P> <P> The cecum is the first section of the colon and involved in the digestion, while the appendix which develops embryologically from it, is a structure of the colon, not involved in digestion and considered to be part of the gut - associated lymphoid tissue . The function of the appendix is uncertain, but some sources believe that the appendix has a role in housing a sample of the colon's microflora, and is able to help to repopulate the colon with bacteria if the microflora has been damaged during the course of an immune reaction . The appendix has also been shown to have a high concentration of lymphatic cells . </P> <P> The ascending colon is the first of four sections of the large intestine . It is connected to the small intestine by a section of bowel called the cecum . The ascending colon runs upwards through the abdominal cavity toward the transverse colon for approximately eight inches (20 cm). </P>

What are the 4 parts of large intestine