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The appendix plays a hidden role in gut health : Shots - Health News A sudden
appendectomy as a child made Heather Smith curious about what the appendix is
for and why it gets inflamed. Now as an anatomy researcher, she's finding
answers.


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SHORT WAVE


YOUR APPENDIX IS NOT, IN FACT, USELESS. THIS ANATOMY PROFESSOR EXPLAINS

February 2, 20245:01 AM ET

Selena Simmons-Duffin

YOUR APPENDIX IS NOT, IN FACT, USELESS. THIS ANATOMY PROFESSOR EXPLAINS

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As an evolutionary anatomist, Heather Smith studies the fossil record of extinct
species. A sudden appendectomy as a child made her curious about what the
appendix is for and why it gets inflamed. Heather Smith hide caption

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Heather Smith


As an evolutionary anatomist, Heather Smith studies the fossil record of extinct
species. A sudden appendectomy as a child made her curious about what the
appendix is for and why it gets inflamed.

Heather Smith

It was the first day of spring break in 1992 in Phoenix, and 12-year-old Heather
Smith was excited for her family's upcoming ski trip.

But before Smith and her family had even packed their snow pants, she realized
she didn't feel good. "I woke up feeling just a little bit nauseous, and I
wasn't sure why. Throughout the course of the day, I started to feel worse and
worse and started to develop pain in the abdomen," she says.

By about midafternoon, her father took her to urgent care. She ended up getting
emergency surgery to have her appendix out.

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Smith still has a small scar from the appendectomy. And after the surgery, she
found herself intrigued by the part of her body she had so suddenly lost. "It
inspired me to wonder: Why do we have this weird little organ in the first
place? What does it do? Why does it get inflamed?"

Smith grew up to be a professor of anatomy at Midwestern University and
editor-in-chief of a journal called The Anatomical Record. And all these decades
later, Smith has made a mark in the field by studying the very organ that threw
off her family's vacation plans in 1992.

She acknowledges that the appendix has a bad rap as a useless organ that can
cause you pain and require emergency surgery. "But it turns out recent research
shows it does have functions that can help us," she says.

NPR's Short Wave spoke to Smith about what the appendix is good for and how a
future where appendicitis can be prevented or treated without emergency surgery
could be on the way.

This conversation has been edited for length and clarity.

What and where is the appendix?

The type of appendix that humans and some primates and rodents have looks like a
little worm. It's about the size of your pinky finger, and it projects off the
cecum, which is the first part of the large intestine.



You can identify the location based on a landmark called McBurney's point. So if
you draw a line between your bellybutton and the part of your pelvis that sticks
out [on the right], two thirds of the way down, that's about where the appendix
is.

How did scientists get the idea that the appendix was useless?

There had been a lot of discussion about what the appendix might do as a
function, whether it served a function, prior to [Charles] Darwin's time. The
[fact] that we can live without it does provide some support for the idea that
it's vestigial and it doesn't really do anything. And so Darwin's interpretation
of it as a vestige was reasonable at the time, given the information that he
had.

But now with modern technology, we can see things like the microanatomy and the
biofilms in the appendix, and we have a better understanding of what it is and
what it's doing.

How has the appendix evolved over time?

If you map the distribution of appendices across a phylogeny — a tree of mammal
life — you can interpret that the appendix has actually evolved independently.
It has appeared independently multiple times throughout mammalian evolution. So
that is evidence that it must serve some adaptive function. It's unlikely that
the same type of structure would keep appearing if it wasn't serving some
beneficial role.

So what are the appendix's beneficial roles?

It turns out that the appendix appears to have two related functions. The first
function is supporting the immune system. The appendix has a high concentration
of immune tissue, so it's acting to help the immune system fight any bad things
in the gut.

The second function that it serves is what we refer to as the safe house. So
this was a hypothesis that was put forward by a team from Duke University in
2007. And they argued that the appendix may serve as a safe reservoir for the
beneficial gut bacteria that we have.



During times of gastrointestinal distress — you know, a diarrhea episode where
all of your good gut bacteria is getting kind of flushed out of the system — the
appendix is kind of this blind tube with a very narrow diameter and narrow
lumen, so the good bacteria doesn't get flushed out of the appendix. The idea is
it's safe during this time of gastrointestinal distress and it can then exit the
appendix and recolonize this good bacteria throughout the rest of the gut.

So the appendix is kind of helping us in two ways, both within the gut: It's
helping to fight off invading pathogens, but also to repopulate the gut with
this beneficial bacteria after gastrointestinal issues.

Why do some people get appendicitis?

Appendicitis is predominantly happening in the industrialized nations of the
world — areas where fiber content of the diet tends to be lower. So one
hypothesis is that, with the lower fiber content, we're more likely to get
little pieces of food that's being digested stuck [inside] the appendix and cut
off blood supply and cause this inflammation.

The other hypothesis that doesn't seem like it's quite as plausible these days
has to do with an old idea called the hygiene hypothesis. The idea is that these
days we do so much oversanitization, with all of our antibacterials and all our
antibiotics that we take, that our immune systems are not developing properly
because they don't have exposure to the full range of pathogens that we would
otherwise. And so the immune system overreacts and panics. And because the
appendix has so much immune tissue, it's one of the areas where this manifests.

Could this new understanding lead to new treatments?

I think there's some promising treatments out there. People are looking into
antibiotics and other ways of treating appendicitis without completely removing
it, given the evidence that is accumulating that it is in fact helpful for your
health to have an appendix. Studies have shown that infections with the really
bad, nasty bacteria C. diff tend to be higher in people who have had their
appendix removed.



So there are health benefits to retaining the appendix. In an ideal world, we
would have a future where we wouldn't have to always remove it.

What have you gained from studying this "weird little organ"?

I think this study has shown me the importance of looking into small anatomical
details. Anatomy is just the study of the body, so you'd think that it's a dead
science. You'd think we know everything about the body, especially the human
body.

But it turns out that there's actually a lot more variation and function and
microanatomical adaptations that haven't been fully realized. So doing just
descriptive studies of exotic animals that have never been described or looking
at small parts of our own bodies that haven't been well documented are
absolutely worthwhile.

 * human anatomy
 * appendix
 * gut health
 * appendicitis
 * immune system

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