What Is the Appendix, and What Does It Do?

The appendix is a thin, roughly four-inch-long tube that’s part of your gastrointestinal (GI) tract. (1)

The GI tract is a complex group of organs, each of which helps your body digest and absorb food.

Your upper GI tract includes your esophagus, stomach, and the first section of your small intestine, called the duodenum.

The lower GI tract is made up of most of your small intestine and all of your large intestine, which includes your colon, rectum, and anal canal. (2)

Where in Your Body Is Your Appendix Located?

Your appendix is located in the lower right part of your abdomen, in an area that doctors refer to as McBurney’s point. If applying pressure on McBurney’s point results in pain or tenderness, your doctor may suspect that you have appendicitis. (3)

The finger-shaped appendix is attached to a part of your large intestine called the cecum — a small pouch typically considered to be the beginning of the large intestine. (1)

What Is the Function of the Appendix?

The muscles lining your GI tract, along with the hormones and enzymes that the system produces, allow your GI tract to break down and process food. Your appendix doesn’t directly help with digestion.

It’s been unclear what role the appendix has in the body, and removal of the organ doesn’t appear to have any negative health consequences.

For many years, scientists believed the appendix was a vestigial organ — one that lost its original function through centuries of evolution.

Researchers thought that no other mammals had an appendix, aside from our closest ape relatives.

What’s more, the cecum (a part of the large intestine) of plant-eating mammals is far larger than it is in humans.

On this basis, Charles Darwin theorized that our distant ancestors also had large ceca, which allowed them to dine on leaves like the herbivores of today.

But as these ancestors shifted to a diet based on fruits, which are easier to digest, their ceca shrank. The appendix, Darwin believed, is just a shriveled up part of the cecum, which evolution hasn’t entirely eliminated. (4)

The ‘Safe House’ Theory of the Appendix

Some scientists now believe the appendix is not useless after all, and may help our guts recover after a gastrointestinal disease strikes.

The appendix contains a particular type of tissue associated with the lymphatic system, which carries the white blood cells needed to fight infections. In recent years, scientists have found that lymphatic tissue encourages the growth of some beneficial gut bacteria, which play an important role in human digestion and immunity.

Studies have also shown that the lining of the gut contains a biofilm, or a thin layer of microbes, mucus, and immune system molecules — and these biofilms appear to be most pronounced in the appendix. (5)

According to the so-called “safe house” theory, the appendix protects a collection of beneficial gut bacteria when certain diseases wipe them out from elsewhere in the GI tract. Once the immune system has rid the body of the infection, the bacteria emerge from the appendix biofilm and recolonize the gut. (6)

A review of the relevant available research published in 2016 concluded that the appendix is not a rudimentary organ but an “important part” of the immune system. (7)

Researchers have recently found that numerous animals, including great apes, other primates, opossums, wombats, rabbits, and certain rodents all have structures similar to the appendix. (8) The appendix, it seems, may have independently evolved in different animals at least 32 times over the course of history, suggesting the organ does have an important function. (4)

Potential Health Issues Involving the Appendix

Sometimes, the appendix can become inflamed and infected, resulting in a condition called appendicitis.

Appendicitis is often the result of an abdominal infection that has spread to the tiny organ, or some kind of obstruction that has blocked the small opening of the appendix. Sources of blockage include, among other things:

• Hard pieces of stool
• Parasites or intestinal worms
• Ingested objects, including air gun pellets and pins
• Abdominal trauma
• GI tract ulcers
• Enlarged appendix lymphatic tissue

The infection or obstruction causes the bacteria in the appendix to grow out of control, and the organ can fill with pus and swell. Appendicitis causes intense abdominal pain and other GI symptoms, including vomiting and diarrhea. Removal of the appendix (an appendectomy) is often the necessary course of action, though increasingly, antibiotics may be recommended and used to treat the infection without the need for surgical intervention — depending on the severity of the case and other health factors in the individual patient. If the problem is left untreated, the pressure in the organ will increase until the appendix ruptures, or bursts.

When the appendix bursts, it spreads its content throughout the abdomen, potentially infecting the peritoneum, which is the silk-like membrane that lines the abdominal cavity. A peritoneum infection, called peritonitis, can then lead to sepsis, a complication that’s potentially deadly if not treated aggressively. (9)

Additional reporting by Deborah Shapiro.