The visceral structures protruding into the envelope of parietal peritoneum are conventionally thought of as intraperitoneal. These structures are covered with visceral peritoneum reflecting off the posterior parietal peritoneum. Technically, the “peritoneal cavity” is the potential space between the parietal and visceral peritoneum, and normally contains only a few ccs of lubricating fluid.
The broad interface between the liver and diaphragm is bounded by a reflection of peritoneum called the coronary ligament. The recess beneath the inferior leaf of coronary ligament is the second deepest location in the peritoneal cavity. The upper abdominal retroperitoneal structures are crossed by the roots of the transverse colon and small bowel mesenteries. Only the duodenal bulb is exposed to the potential peritoneal space. Anterior perforation of a duodenal ulcer leads to peritonitis. Retroperitoneal rupture of the remainder of the duodenum may be occult until sepsis ensues. The tail of the pancreas lies in the posterior wall of the lesser sac (omental bursa).
At the lower end of the abdominal cavity, the peritoneum reflects off the upper third of the rectum, creating the rectovesical recess in the male and rectovaginal recess (pouch of Douglas) in the female. This is the most dependent recess of the peritoneal cavity and a common site of abscess after perforated viscus. Perforation of the rectum above 12 cm from the anal verge results in peritonitis, while perforation below is extraperitoneal and can sometimes be managed non-operatively.