The peritoneal cavity is a potential space between the parietal peritoneum and visceral peritoneum, that is, the two membranes that separate the organs in the abdominal cavity from the abdominal wall. It is one of the spaces derived from the coelomic cavity of the embryo, the others being the pleural cavities around the lungs and the pericardial cavity around the heart.
The peritoneal cavity is the largest serosal sac in the body and secretes approximately 50 ml of fluid per day. This fluid acts as a lubricant and has anti-inflammatory properties.
Read more about Peritoneal Cavity: Clinical Significance