What condition involves inflammation of the peritoneum?

Peritonitis is the condition that specifically involves inflammation of the peritoneum, which is the serous membrane lining the abdominal cavity and covering the abdominal organs. This inflammation can result from various causes, including infections, such as bacterial infections, or can arise from perforation of abdominal organs, leading to the release of bacteria or intestinal contents into the peritoneal cavity.

In contrast, the other conditions listed involve different mechanisms and areas of the digestive system. Diverticulitis refers to the inflammation of diverticula, which are small pouches that can form in the colon, but it does not inherently involve the peritoneum. Cirrhosis is a chronic liver condition characterized by scarring of the liver tissue, which does not directly relate to inflammation of the peritoneum. Lastly, irritable bowel syndrome is a functional gastrointestinal disorder that includes symptoms such as cramping, abdominal pain, and altered bowel habits, but it is not associated with inflammation of the peritoneal lining.

Thus, the specificity of peritonitis in relation to the peritoneum makes it the correct answer in this context.