peritoneum

The peritoneum is a serous membrane that lines the abdominal cavity and envelops most intraabdominal organs. It consists of a layer of mesothelial cells (simple squamous epithelium) supported by connective tissue. The peritoneum forms two continuous sheets: the parietal peritoneum, which lines the inner abdominal wall, and the visceral peritoneum, which covers many abdominal organs. The space between these layers is the peritoneal cavity, normally containing a small amount of lubricating fluid.

Organs are classified as intraperitoneal (within the peritoneal cavity and suspended by mesenteries) or retroperitoneal (posterior to the peritoneum). The mesenteries, omenta, and mesocolons are folds of peritoneum that attach organs to the body wall or to other organs, and they provide conduit for nerves and blood vessels. The greater omentum hangs from the greater curvature of the stomach and covers the intestines; the lesser omentum connects the stomach to the liver.

The peritoneal cavity is subdivided into the greater sac and the lesser sac (omental bursa), with recesses such as the hepatorenal recess. Functions of the peritoneum include lubrication for free movement of viscera, a conduit for blood vessels and nerves, immune defense via resident macrophages, and fat storage in the omenta.

Clinical relevance includes peritonitis (inflammation of the peritoneum), ascites (fluid accumulation), and the use of the peritoneal membrane in peritoneal dialysis. Adhesions can form after surgery, altering organ movement. Developmentally, the peritoneum arises from the mesoderm and coelomic lining of the embryonic cavity, and its innervation and blood supply reflect the regional somatic and autonomic patterns of the abdomen.