Appendix

Appendix, a worm-shaped tube branching off the cecum, the first part of the large intestine. It is located on the lower right side of the abdomen and is usually about 9 cm (about 3.5 in) long, with a thick wall. Only humans and apes have an appendix.

Historically, the appendix had no known function in human biology. Many scientists believed that the human appendix at one time served a useful purpose that was gradually lost through evolution. Then in 2007 a group of scientists announced that the appendix houses beneficial bacteria essential to the digestive system. According to this research, the appendix repopulates the gut with healthy bacteria in response to conditions such as dysentery and diarrhea.

For reasons not fully understood, the appendix can become infected and filled with pus—particularly in children, teenagers, and young adults—resulting in appendicitis. Symptoms of appendicitis include pain and cramps in the area between the right hip bone and the navel, fever, nausea and vomiting, constipation, and diarrhea. The treatment is surgical removal of the appendix, known as appendectomy. If the appendix wall ruptures, infection may spread to the abdominal cavity, causing peritonitis, an inflammation of the abdominal lining. Acute peritonitis is often fatal if left untreated.