Appendicitis is a painful swelling and infection of the appendix. The appendix is a fingerlike pouch attached to the large intestine and located in the lower right area of the abdomen. Scientists are not sure what the appendix does, if anything, but removing it does not appear to affect a person’s health. The inside of the appendix is called the appendiceal lumen. Mucus created by the appendix travels through the appendiceal lumen and empties into the large intestine.