Peritoneum

The peritoneum has two layers: the parietal peritoneum lines the inner surface of the abdominal wall, while the visceral peritoneum covers the abdominal organs. Together, they enclose the peritoneal cavity filled with serous fluid. These layers form the body's largest serous membrane, protecting and supporting abdominal structures.

Peritoneal folds—including the greater omentum, falciform ligament, lesser omentum, mesentery, and mesocolon—bind abdominal organs together and attach them to the abdominal cavity walls. These folds carry blood vessels, lymphatic vessels, and nerves that supply nutrients and facilitate organ movement while maintaining structural stability.

The greater omentum is the longest peritoneal fold, hanging from the stomach and wrapping around the small intestines. Rich in adipose tissue, it covers the transverse colon and small intestine coils. It acts as a protective barrier, isolating infections and inflammation within the peritoneal cavity to prevent spread.

The peritoneal cavity contains a thin layer of peritoneal fluid that acts as a lubricant, reducing friction between organs. This lubrication allows smooth movement and prevents organs from adhering to each other or the abdominal wall, enabling normal physiological function and mechanical and chemical digestion in the small intestine.

The lesser omentum connects the stomach and duodenum to the liver, containing blood vessels and bile ducts that aid digestion and nutrient absorption. The mesentery, a fan-shaped fold, attaches the jejunum and ileum to the posterior abdominal wall while carrying blood vessels, nerves, and lymphatics that supply the intestines.

Peritonitis is severe inflammation of the peritoneum caused by infection-introducing microbes into the peritoneal cavity. It can result from unintentional or surgical injuries to the abdominal wall, or from rupture of hollow organs like the intestine or appendix. People undergoing peritoneal dialysis face elevated peritonitis risk.

The peritoneal cavity contains immune system cells, such as macrophages, that defend against infections and foreign substances. The peritoneum also provides absorbent and secretory capabilities, allowing it to absorb nutrients and drugs from the gastrointestinal tract while secreting substances for various physiological processes.