https://www.npr.org/sections/health-shots/2024/02/02/1228474984/appendix-function-appendicitis-gut-health

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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

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.

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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