Discusses appendicitis and the appendix function.
Someone once said that the only function of the appendix is financial support of the surgical profession. About 7 percent of the population in developed countries will suffer from appendicitis in their lifetime, but appendicitis seems to be rare in undeveloped countries. It is unclear if diet or some other factor contributes to this difference.
In humans, the appendix is a wormlike pouch, three-and-a-half inches long on average, attached to the first part of the large intestine. In herbivorous mammals, such as rabbits, a much larger analogous structure houses bacteria that help break down cellulose, a large plant molecule. The appendix is present in many vertebrates, including other primates.
The human appendix does not contain cellulose-digesting bacteria, so humans cannot digest cellulose (which is why lettuce is roughage). Therefore, the appendix is often called a vestigial organ—a structure that has become diminished in size and lost its original physiological function.
That does not mean the human appendix has no function. Of the many functions hypothesized, a role in immunity is considered the most likely, although this remains controversial. The appendix, along with other parts of the digestive system, produces immune system cells, which can respond to ingested, disease-causing microbes. Whether the appendix contributes significantly to the immune response is unknown, since the lack of an appendix does not cause any obvious health problems.