Peritonitis

Peritonitis is inflammation of the peritoneum. The peritoneum is a thin tissue that lines the inside of the abdominal wall and also wraps around most of the organs in there. Picture a thin liner that covers the walls of a box and also covers whatever is packed inside it. That's the peritoneum, and when it becomes inflamed, it's called peritonitis.

The space that liner encloses, the abdominal cavity, is normally sterile, meaning it has no germs. The intestine, on the other hand, carries its own bacteria. Think of a drainpipe running through a freshly cleaned room: as long as the pipe is intact, the room stays clean, but if a hole opens up, whatever the pipe was carrying spills out. A hole in the wall of the digestive tract is called a perforation, and it's the most common way germs get in. Once inside, the gut bacteria release endotoxins, toxic substances that set off an exaggerated chain reaction of inflammation, like dominoes knocking each other over. When that inflammation spreads beyond the abdomen and reaches the whole body, it's called sepsis.

When peritonitis comes from another problem, such as an appendix that bursts, it's called secondary peritonitis. The appendix is the small, finger-shaped pouch that sticks out from the large intestine. Another form, spontaneous bacterial peritonitis, shows up in people with ascites, meaning fluid that has built up between the lining of the abdomen and the organs.