The appendix is part of the large intestine. It is a tubular formation projecting from the cecum (the beginning of the large bowel). It contains lymphatic tissue (part of the immune system) and secretes mucus.
Diverticular disease is the condition of having (sac like) projections in the wall of the colon. The increased pressure in the bowel lumen results in mucosa projections through weaknesses of muscle layers in the colon wall. They look like the “blisters” on a car’s tire.