The parietal peritoneum covers the abdominal and pelvic walls as well as the diaphragm. As the outermost layer of the peritoneum, the parietal peritoneum demarcates an abdominopelvic cavity, also known as the peritoneal cavity, that contains almost every organ of the abdomen and pelvis.
Depending on whether the organs are completely or partially covered by the peritoneum, they are classified as intraperitoneal or
retroperitoneal organs. Intraperitoneal refers to organs or structures that are completely covered by the
visceral peritoneum and include organs such as the liver, stomach, and
transverse colon. On the other hand, retroperitoneal organs are organs that are not located within the peritoneal cavity and, therefore, are only partially covered by the parietal peritoneum. More specifically, only the anterior wall is covered by the parietal peritoneum. These organs are further classified as primary and secondary retroperitoneal organs depending on their position during development. The primary retroperitoneal organs develop and remain outside of the peritoneal cavity and include the
adrenal glands, kidneys, and
ureter as well as the
abdominal aorta,
inferior vena cava, and their respective branches. The secondary retroperitoneal organs, which initially develop intraperitoneal and become
retroperitoneal structures throughout development, include the
pancreas, the ascending and
descending colon, and the distal part of the
duodenum.
