Final answer:
Peritonitis causes a rigid abdomen due to the inflammatory response of the peritoneum when it is exposed to substances like gastric juices, blood, or bacteria from a breach in the alimentary canal. Emergency surgery and antibiotics are needed to treat this life-threatening condition, which still has a high mortality rate.
Step-by-step explanation:
The characteristic rigid abdomen found in a patient with peritonitis is caused by the inflammation of the peritoneum, which can occur due to a breach in the wall of the alimentary canal. This breach allows contents such as gastric juices, blood, or bacteria to enter the peritoneal cavity, leading to chemical, hemorrhagic, or bacterial peritonitis. These substances and the resulting infection trigger a severe inflammatory response, causing the abdominal wall muscles to tense up in an effort to protect the inner organs, leading to rigidity.
Common causes of peritonitis include a perforated stomach ulcer, ruptured tubal pregnancy, traumatic injury to the liver or spleen, or bacterial infections associated with appendicitis, colonic diverticulitis, and pelvic inflammatory disease (PID). This condition is life-threatening and requires emergency surgery and intensive antibiotic therapy to treat the underlying cause. While improvements in medical care have reduced mortality rates from peritonitis, they still range from 30 to 40 percent.