Vestigial hollow tube attached to the cecum of the large intestine. The human appendix, usually 3–4 in. (8–10 cm) long and less than 0.5 in. (1.3 cm) wide, has no digestive function. Its muscular walls expel their own mucous secretions or any intestinal contents that enter it. Blockage of the opening may prevent expulsion and cause appendicitis: fluids collect, bacteria propagate, and the appendix becomes distended and inflamed; tissue in the appendix begins to die, and the organ may burst, causing peritonitis. Its symptoms may begin with moderate pain in the upper abdomen, about the navel, or all over the abdomen. Nausea and vomiting may then develop. The pain may shift to the right lower abdomen. Fever is usually present but is seldom high in the early phases. Differentiating acute appendicitis from other causes of abdominal pain requires careful examination. Treatment is removal of the appendix (appendectomy).
Learn more about appendix with a free trial on Britannica.com.
The term "vermiform" comes from Latin and means "worm-like in appearance".
The vermiform appendage—in which some recent medical writers have vainly endeavoured to find a utility—is the shrunken remainder of a large and normal intestine of a remote ancestor. This interpretation of it would stand even if it were found to have a certain use in the human body. Vestigial organs are sometimes pressed into a secondary use when their original function has been lost.
One potential ancestral purpose put forth by Darwin was that the appendix was used for digesting leaves as primates. Over time, we have eaten fewer vegetables and have evolved, over thousands of years, for this organ to be smaller to make room for our stomach. It may be a vestigial organ of ancient man that has degraded down to nearly nothing over the course of evolution. Evidence can be seen in herbivorous animals such as the Koala. The cecum of the koala is attached to the juncture of the small and large intestines and is very long, enabling it to host bacteria specific for cellulose breakdown. Early man’s ancestor must have also relied upon this system and lived on a diet rich in foliage. As man began to eat more easily digested foods, they became less reliant on cellulose-rich plants for energy. The cecum became less necessary for digestion and mutations that previously had been deleterious were no longer selected against. These alleles became more frequent and the cecum continued to shrink. After thousands of years, the once-necessary cecum has degraded to what we see today; the appendix.
Evolutionary theorists have suggested that natural selection selects for larger appendices because smaller and thinner appendices would be more susceptible to inflammation and disease.
Appendicitis (or epityphlitis) is a condition characterized by inflammation of the appendix. Pain often begins in the center of the abdomen, corresponding to the appendix's development as part of the embryonic midgut. This pain is typically a dull, poorly localised, visceral pain.
As the inflammation progresses, the pain begins to localise more clearly to the right lower quadrant, as the peritoneum becomes inflamed. This peritoneal inflammation, or peritonitis, results in rebound tenderness (pain upon removal of pressure rather than application of pressure). In particular, it presents at McBurney's point, 1/3 of the way along a line drawn from the Anterior Superior Iliac Spine to the Umbilicus. Typically, point (skin) pain is not present until the parietal peritoneum is inflamed as well. Fever and an immune system response are also characteristic of appendicitis.
Many cases of appendicitis require removal of the inflamed appendix, either by laparotomy or laparoscopy. Untreated, the appendix may rupture, leading to peritonitis, followed by shock, and, if still untreated, death.
The surgical removal of the vermiform appendix is called an appendicectomy (or appendectomy). This procedure is normally performed as an emergency procedure, when the patient is suffering from acute appendicitis. In the absence of surgical facilities, intravenous antibiotics are used to delay or avoid the onset of sepsis; it is now recognized that many cases will resolve when treated non-operatively. In some cases the appendicitis resolves completely; more often, an inflammatory mass forms around the appendix. This is a relative contraindication to surgery.