Today, the appendix is recognized as a highly specialized organ with a rich blood supply. This is not what we would expect from a degenerate, useless structure.
The appendix contains a high concentration of lymphoid follicles. These are highly specialized structures which are a part of the immune system. The clue to the appendix’s function is found in its strategic position right where the small bowel meets the large bowel or colon. The colon is loaded with bacteria which are useful there, but which must be kept away from other areas such as the small bowel and the bloodstream.
Through the cells in these lymphoid follicles, and the antibodies they make (see box below), the appendix is ‘involved in the control of which essential bacteria come to reside in the caecum and colon in neonatal life’.6 Like the very important thymus gland in our chest, it is likely that the appendix plays its major role in early childhood. It is also probably involved in helping the body recognize early in life that certain foodstuffs, bacterially derived substances, and even some of the body’s own gut enzymes, need to be tolerated and not seen as ‘foreign’ substances needing attack.
The appendix is an ugly, wormy little sac hanging off your large bowel that serves no purpose beyond occasionally becoming inflamed and trying to kill you. It's a vestige of a structure that was useful way back in our evolutionary history, but which evolution never bothered to get rid of.
Or so we were taught. It turns out, back in 1980, scientists found evidence that it isn?t vestigial at all. Anatomical studies failed to find anything it could be a vestige of. Other mammals don?t have them, except our closest ape relatives - and rabbits. This suggests the appendix is there for a reason. But what?
Bill Parker and colleagues at Duke University in North Carolina in the US think the appendix is a "safe house" for good gut bacteria, which would otherwise all be lost to bouts of diarrhoea. They found that healthy appendices are well endowed with immune tissue, and biofilms - the adherent colonies of beneficial microbes that have been found throughout biology, most recently lining much of the large bowel.
Now, as we all know, the small intestine leads into the large intestine, but plugs into the side of the larger tube, leaving its blind end hanging below the join. That blind end, and especially the narrow appendix leading off it, are largely protected from the normal flow of gut contents. This, Parker observes, makes it well placed to harbour beneficial bacteria so they can re-colonise a recently flushed gut.
Which makes you wonder why people without their appendix don't get unusual ailments. Maybe people in industrialised countries, who are most likely to have had an appendectomy, don't need the reserve bacteria because they are unlikely to get extreme diarrhoeal diseases like, say, cholera.
Parker sees something else in the statistics. Fully 6% of people in industrialised countries have had the thing out, but appendicitis is relatively rare in poor countries. Perhaps this is due to differences in diet, with more roughage making for generally healthier guts? Or perhaps, suggests Parker, appendicitis is another product of our clean society, just like allergies and asthma - both the result of an immune system that turns on us.