Wednesday, July 30, 2014

What's the appendix for?

My appendix was removed when I was five years old, at the hands of a well-meaning country doctor who thought it would cure my chronic childhood tummy aches. The finest medical scientists at the time knew, of course, that the appendix is a vestigial organ, an evolutionary leftover that was not needed in modern humans and would probably, in future generations, evolve itself away. I guess I’m proof, half a century later, that those scientists were right: you can live a perfectly healthy life (well, almost) without an appendix.

Still, the idea has always nagged at me and lately I’ve started reading the fascinating science writer Rob Dunn, who I learned about through one of his old blog posts at Scientific American. He summarizes his evidence in his book The Wild Life of Our Bodies: Predators, Parasites, and Partners That Shape Who We Are Today, but the basic idea is that the appendix helps re-populate your gut bacteria after a major crash — a bout of food poisoning, say, or some terrible infection that takes over before your immune system has a chance to respond.

What’s inside a healthy person's appendix anyway?  Answer: immune tissue, various (normally good-for-you) bacteria, and IgA antibodies — all stuff that seems like you wouldn’t want to just cut out of a person, like that long-forgotten surgeon did to me.

Dunn’s book is interesting throughout, and besides the appendix discussion here are some additional things I learned:

  • Humans have taste buds in their gut (see Wu, S. et all in PNAS 99:2392-2397 . What are they doing in there? Who knows, but catfish have them all over their bodies. Maybe the sense of taste includes some measure of what’s already in our tummies.
  • Specially-modified mice that have no bacteria in their guts seem to live okay, but they need 30% more calories to get the same amount of nutrients as normal mice.
  • You may think you react with similar horror to something violent as you do to something pathogenic.  You feel the same stress, same heart rate increase and other body signs either way.  But your immune system can tell the difference (as measured by changes in measures of immune system response). 
There’s much more to like in the book as well as the other Rob Dunn writings. Definitely recommended.
By the way, if you would like to know more about what’s on my reading list, and (especially if you have suggestions for things I might like!) please follow me on Goodreads.