Ask A Scientist

My friend got their appendix taken out. What does it do and is it needed?

Asked by: Summer Manville
School: Owego Elementary School
Grade: 5
Teacher: Trevor McCloe
Hobbies/Interests: I love animals and I collect rocks.
Career Interest: Animal cop

Answer from Karl Wilson

Professor of Biology, Binghamton University

Ph.D. school: University at Buffalo
Interests/hobbies:  Paleontology, photography, cooking
Web page address:

First off, your friend should be fine without his/her appendix.  In fact, some people are born without an appendix and do quite well. It has long been considered a vestigial organ, which means that is once had a purpose but is no longer needed.  The appendix is a finger-like dead-end tube protruding from the end of the caecum.  The caecum is in turn a pouch-like organ where the large and small intestines join.  In humans the caecum is relatively small, but in many herbivores (plant eaters), such as the rabbit, the caecum may be larger than the large intestine.  Symbiotic bacteria housed in the caecum are responsible for the digestion of the cellulose making up the bulk of plant cell walls.  The bacteria produce enzymes that digest the cellulose into glucose that can be used by the bacteria and the host animal.  In humans the caecum is proportionately much smaller, and this cellulose digestion contributes very little to our nutrition. Most of the cellulose we eat is not digested and contributes necessary bulk to our solid waste. That is why fiber is important in our diet. The appendix has been hypothesized to perhaps contribute to the immune system guarding the intestines from infection.  However, it is so small it contributes very little to this process. Recently, researchers at Duke University Medical School have suggested that the appendix does have a function in maintaining the normal complement of bacteria in the gut.  The intestine may contain up to 500 species of bacteria in the normal individual.  These bacteria synthesize some of the vitamins that we require (e.g. biotin and vitamin K), help digest some food components, and are thought to prevent the growth of invading bacteria that can cause sickness.  The researchers at Duke have theorized that the appendix serves as a sort of “a good safe house for bacteria” of these beneficial bacteria.  This could have been important in early man, or even today under less then hygienic conditions.  Infections by food and water borne bacteria could be common, and the resulting diarrhea would flush the intestines of bacteria, including the beneficial ones.  Once the person recovers, the bacteria stored in the appendix would reseed the gut with the beneficial bacteria.  This function is, however, probably not as important in modern living as it was early in the evolution of our species.  Modern hygienic practices in handling food and waste have greatly reduced the incidence of this type of disease.  Also, because of our relatively high population densities (compared to early man) we can pick up the bacteria to repopulate the intestines relatively easily by day-to-day contact with other people.  

Last Updated: 9/18/13