The appendix is shaped like a hollow finger. The open end communicates with the inside of the intestine. The inside lining of the appendix produces mucus and fluid, which flows from the inside of the appendix, into the intestine. This flow of mucus and fluids keeps the bacteria from growing inside the appendix. The appendix has no known function in the human body.

Appendicitis is caused by a sequence of events:

• Stool blocks the opening of the appendix.
• Mucus and fluid buildup inside the appendix.
• The bacteria are not cleared from the appendix and they start to multiply.
• As the fluid builds up, the pressure inside the appendix increases.
• The appendix starts to swell.
• The pressure inside the appendix rises above the blood pressure.
• Blood stops flowing through the appendix.
• The bacteria invade the wall of the appendix.
• The bacteria start to destroy the appendix. The resulting swelling and infection is called appendicitis.

As the wall of the appendix is destroyed and the appendix continues to swell, the appendix can burst, spreading the infection beyond the appendix.