Peritoneum is a thin and smooth plasma membrane covering the abdominal and pelvic cavity wall and the surface of abdominal and pelvic organs. It has the functions of secretion, protection, and repair. Peritoneum is a plasma membrane, translucent, covering the abdominal and pelvic cavity wall and the surface of abdominal and pelvic organs. It can be divided into wall peritoneum and dirty peritoneum. The peritoneum lining the wall of the abdominal and pelvic cavity is called the mural peritoneum; the peritoneum returning from the mural peritoneum and covering the surface of the abdominal and pelvic organs is called the visceral peritoneum. The peritoneum has the functions of secretion, protection and repair. The peritoneum can secrete a small amount of plasma, which has the function of lubrication and reducing friction. The plasma contains a large number of macrophages, which phagocytose bacteria and harmful substances. The plasma secreted by the peritoneum contains cellulose, which promotes wound healing and limits inflammation. Specific inflammation irritates the peritoneum and can cause localized pain, which can help in diagnosis. For example, pain in the right lower abdomen is often the result of appendiceal inflammation that irritates the peritoneum in that area leading to peritoneal irritation sign, which is characterized by tightness of the abdominal muscles in that area, pressure and rebound pain. If you have pain in the abdomen, you need to go to the hospital and follow the doctor’s instructions after clarifying the cause of the pain.