Short Wave - This Scientist Figured Out Why Your Appendix Isn't Useless

Episode Date: February 2, 2024

Back in the day, many of us heard that the appendix is a vestigial organ — at best, a body part that lost its purpose all those many years ago. At worst, an unnecessary clinger-on to the human body that, when ruptured, could be life threatening. But what if that narrative is wrong?Heather Smith became obsessed with the appendix after hers was removed at age 12. After years of anatomy research, she's found that the appendix is not, in fact, useless. Reporter Selena Simmons-Duffin is in the host chair today to get the scoop on all things appendix. Think it's time to give another part of the human body its due? Email us at [e-mail] — we'd love to hear about it!See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, shortwavers. I'm Selena Simmons-Duffin in the host chair today. Let's travel back in time to the early 90s. It's springtime in Phoenix, Arizona, and 12-year-old Heather Smith is in good spirits. It's the first day of her spring break, and even though it's been hot, like 80 degrees every day hot, her family is going on vacation, and there's going to be snow. It's the Sonoran Desert. So going on a skiing trip is really exciting.

That's their plan, but before Heather and her family have even packed their snow pants, she realizes she doesn't feel good. I woke up feeling just a little bit nauseous, and I wasn't sure why, and then throughout the course of the day, I started to feel worse and worse. Her abdomen started to hurt. Her dad, a physicist, put together that she might have appendicitis. So he took me to urgent care, who sent me to the emergency room. And by about 10 o'clock that same night, I had already entered surgery to have my appendix out. I was in the hospital for several days. I still have a small scar on my abdomen.

The ski trip never happened. The family hung out at home in Phoenix instead. And afterward, Heather found herself kind of obsessed with the appendix. Why do we have this weird little organ in the first place? What does it do? Why does it get inflamed? Heather Smith grew up and became a scientist like her dad. She is a professor of anatomy at Midwestern University. The campus is near her hometown of Phoenix. And I'm the editor-in-chief of a journal called The Anatomical Record. That sounds so official, the anatomical record. It's like you're in charge of all things anatomy. We do publish all things anatomy. I love it. It's so diverse. We get all kinds of interesting topics.

Of all those topics, Heather Smith has really made a mark in the field by studying the very weird little organ that threw off her family's ski plans in 1992. She acknowledges you may not think very pleasant things when you think of the appendix. We tend to hear about it in the context of appendicitis and appendectomies, surgically removing the appendix. So we don't tend to think of it as being terribly useful. But it turns out recent research shows it does have functions that can help us. Today on the show, the days of thinking of the appendix as a useless organ that can kill you with little notice are over. We'll explain 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. You're listening to Shortwave, the science podcast from NPR.

Okay, Heather, what is the appendix in the human body? Where is it? What does it look like? So the type of appendix that humans and primates, some primates and rodents have, looks like a little worm. It's about the size of your pinky finger, and it projects off the seacom, which is the first part of the large intestine. And you can sort of identify the location based on a landmark called McBurney's Point. So if you draw a line between your navel, your belly button, and the anterior superior iliac spine, which is basically the part of your pelvis that sticks out anteriorly. so you can kind of feel that bump sticking out. If you draw a line on the right between those two,

two thirds of the way down, that's about where the appendix is. I just wanted to note that one of your papers shows a diagram of different appendices and different species, and it's kind of wild. It's like all of these squiggly lines. It looks like a calligraphy exercise or something like that. Yeah, so there are actually several different types of appendices. So humans have this vermiform type, but rabbits and hairs and other lagomorphs have this elongated sechum that kind of tapers into an appendix

rather than being a separate kind of projection. And then in animals like marsupials and monotrems, so things like the wombat and the ekegon. They have this tiny little projection that just comes off the large intestine, but they don't really have a sechum at all. So it turns out there are actually many different ways throughout the mammal kingdom to have an appendix. Okay, so for a long time, people thought that the appendix was useless, basically like this leftover organ. And it seems to me that Charles Darwin was one of the people who kind of created the sense that that's what this was for, basically nothing. Yeah, there'd been a lot of discussion about what the appendix might do as a function, whether it served a function prior to Darwin's time. And the idea that, you know, we can live without it does provide some support for the idea.

that it's vestigial and it doesn't really do anything. But now with modern technology, we can see things like the micro anatomy and the biofilms in the appendix. And we have a better understanding of what it is and what it's doing. So I understand that some of the research you've done on the appendix has to do with how it's evolved over time and through species. So why is that illuminating, that kind of line of inquiry? So my research team was in. interested in looking across mammals at the distribution of which mammals have an appendix and what type of appendix they'd have, whether it's vermiform or this elongated seacum, and inferring how the appendix might have evolved over time. And what we found, 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. So it has appeared. independently multiple times throughout mammalian evolution. So that is evidence as well 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. And what are those beneficial roles? Like what have you been able to dig up that makes the appendix more useful and interesting than originally thought? So it turns out that the appendix appears to have two kind of related functions. So the first function is supporting the immune system.

So the appendix, it turns out, has a high concentration of immune tissue. So it's acting to kind of help the immune system fight any bad, you know, 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, Bowlinger at all, in 2007, and they argued that the appendix may serve as kind of a safe reservoir for the beneficial gut bacteria that we have. So during times of gastrointestinal distress, you know, a diarrheal 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. So the idea is it's safe during this time of gastrointestinal distress, and it can then exit the appendix and kind of recolonize this good bacteria throughout the rest of the gut. So the appendix is kind of helping us in two ways. It's helping to fight off invading pathogens, but also to repopulate the gut with this good beneficial bacteria after gastrointestinal issues. Hmm. So it's like a little pocket that you're. intestine keeps some good bacteria handy. Exactly. So there's still a mystery is related to the appendix. As far as I know, there's not really any understanding about why one person gets

appendicitis and one person doesn't. So it seems like appendicitis is predominantly happening in sort of the industrialized nations of the world. So areas where fiber content of the diet tends to be lower. And so one hypothesis is that, you know, with the lower fiber content, we're more likely to get little pieces of digesta, so, you know, food that's being digested, little sort of fecal pellets that get stuck in the lumen in the diameter of 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 with the hygiene hypothesis is that these days we do so much

over sanitization 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 just kind of overreacts and panics. And because the appendix has so much immune tissue, it's one of the areas where this manifests. Okay, so the appendix clearly serves a purpose. And there are a couple of different ways that that could work. But it is okay to take it out, right? Like, people can function without it. Right. That's one of the reasons that it was, the appendix was thought to be vestigial for so long as we observe that you can live just fine without it. I've been without mine for 30 years and I am very healthy. But if you think about other organs, you know, you can live without a spleen.

You can live without a nose, but it doesn't mean that they aren't helpful if you do have them. Certainly, yeah. Is it possible that this new understanding of what the appendix does might lead to new approaches to appendicitis? Because nowadays, it's laparoscopic surgery. You can be in and out. But it's still surgery. You're still having part of your body removed. Do you think there's a future in which appendicitis maybe doesn't happen as often?

or if it does happen, it doesn't lead to this emergency surgery that is still the treatment now? I think there's some promising treatments out there. People are looking into antibiotics and other types of ways of treating appendicitis without completely removing it. And I think somewhere down the line that might be the case, given the evidence that is accumulating, that it is, in fact, helpful for your health to have an appendix. You know, 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 in an ideal world, we would have a future where we wouldn't have to always remove it.

I guess I have a bigger picture question here, which is what do you, what have you gained from this line of research? I think this study has shown me the importance of looking into small anatomical detail. So anatomy is just the study of the body. And so you'd think that it's kind of 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 micro-anatomical adaptations that haven't been fully realized. Doing just descriptive studies, you know, 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. I feel like maybe operation needs

to be updated. That game, you know, for kids needs to be updated with all of this new information. Right. Absolutely. It's like old globes. You've got to keep it up to speed. Heather Smith, thank you so much for telling us all about the appendix and the things that it's good for that have been overlooked. Absolutely. Thank you for your time. This episode was produced by Margaret Serino and edited by our showrunner, Rebecca Ramirez. It was fact-checked by Britt Hansen. Carly Strange was the audio engineer. I'm Selena Simmons-Steffen.

Thanks for listening to Shortwave from NPR.