appendix
Meaning of appendix: Long dismissed as a useless leftover, it is now thought to hold immune tissue and shelter a reserve of gut bacteria.
Definition of appendix
The appendix is a narrow, blind ended tube, usually a few inches long, that hangs from the cecum, the pouch where the large intestine begins. It has no essential role in digestion and can be removed without lasting consequence, but its wall is packed with immune tissue, and it is the site of appendicitis.
Where is it, and what does it do?
It opens off the cecum in the lower right abdomen, though the free end can sit in several different positions: tucked behind the cecum, hanging down toward the pelvis, or lying across the front. That variation explains why appendicitis does not always feel the same from one person to the next.
Its function is no longer considered to be nothing. The wall contains dense lymphoid tissue of the sort that lines the gut elsewhere, part of the immune system that samples what passes through and helps shape the response to it. A second idea, supported but not settled, is that the narrow dead end acts as a refuge for beneficial gut bacteria, holding a reserve population that can repopulate the colon after an illness flushes it out. Neither role is essential, which is consistent with people living normally without one.
Why does it become inflamed?
| Stage | What is happening | What is felt |
|---|---|---|
| Obstruction | The opening is blocked by hardened stool, swollen lymphoid tissue or, rarely, a tumor; secretions build up behind it | Vague, poorly located pain around the navel, with nausea and loss of appetite |
| Inflammation | Pressure rises, blood supply to the wall is squeezed and bacteria multiply and invade it | Pain settling into the lower right abdomen, sharp and tender to touch |
| Perforation | The wall gives way and contents spill into the abdominal cavity | Pain spreading more widely, with fever and a rigid abdomen |
Why does the pain move?
The two stages of pain come from two different nerve supplies. A stretched hollow organ sends signals through nerves that cannot localize well, so early pain is felt near the midline regardless of where the organ actually sits. Once inflammation reaches the lining of the abdominal wall itself, which is served by nerves that localize precisely, the pain relocates to the spot overlying the appendix. That migration is one of the more distinctive patterns in abdominal medicine. Removal is among the most common emergency abdominal operations and is usually done through laparoscopic surgery.
Also known as
Used in a sentence
The patient presented with right lower quadrant pain concerning for appendicitis involving the appendix.
Good to know
Appendicitis is often suspected when abdominal pain shifts from a vague, central location to a more localized area in the lower right abdomen, a pattern that reflects the appendix's typical anatomical position.
Word origin
Where “appendix” comes from
From Latin appendix, meaning an addition or something attached, from appendere, formed from ad- (to) and pendere (to hang).