The appendix plays a hidden role in gut health: bullets
It was the first day of spring break in 1992 in Phoenix, Arizona, and 12-year-old Heather Smith was excited about her family’s upcoming ski trip
But before Smith and her family packed their snow pants, she realized she wasn’t feeling great. “I woke up feeling a bit nauseous and I wasn’t sure why,” she says. “Over the course of the day, I started feeling worse and worse, and I started having stomach pain.”
By about mid-afternoon, her father took her to urgent care. She ended up having emergency surgery to take out her appendix.
Smith still has a small scar from his appendectomy. After surgery, she found herself fascinated by the part of her body she had 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 become inflamed?”
Smith grew up to become a professor of anatomy at Midwestern University and editor-in-chief of a journal called Anatomical record. All these decades later, Smith left a mark on the field by studying the same member who canceled her family’s vacation plans in 1992.
She admits that the appendix has a bad reputation as a useless organ that can cause you pain and require emergency surgery. “But it turns out that recent research shows that it has functions that can help us,” she says.
NPR’s Short Wave spoke to Smith about the benefit of the appendix, and how a future could be where appendicitis can be prevented or treated without emergency surgery on the way.
This conversation has been edited for length and clarity.
What and where is the accessory?
The appendix type in humans and some primates and rodents resembles a small worm. It’s about the size of your pinky finger, and emerges from the cecum, the first part of the large intestine.
You can determine the location based on a landmark called McBurney Point. So, if you draw a line between your belly button and the part of your pelvis that sticks out (on the right), two-thirds of the way down, that’s where your appendix is.
How did scientists come up with the idea that the appendix is useless?
There was a lot of discussion about what the appendix could do as a function, and whether it served a function, before the time of (Charles) Darwin. The (fact) that we can live without it provides some support to the idea that it is a vestigial thing and doesn’t really do anything. So Darwin’s interpretation of it as a remains was plausible at the time, given the information he had.
But now with modern technology, we can see things like the microanatomy and biofilms in the appendix, and we have a better understanding of what they are and what they do.
How did the appendix develop over time?
If you plot the distribution of appendages across the lineage—the mammalian tree of life—you can interpret that the appendix actually evolved independently. It has appeared independently, several times during mammalian evolution. This is evidence that it must serve some adaptive function. The same type of structure is unlikely to continue to exist if it does not serve a useful role.
So what beneficial roles does the supplement play?
It turns out that the supplement appears to have two related functions. The first function is to support the immune system. The appendix contains a high concentration of immune tissue, so it works to help the immune system fight off any bad things in the intestines.
The second function it serves is what we refer to as a safe house. So this was a hypothesis that a team at Duke University put forward in 2007. They saw that the appendix might serve as a safe repository for our beneficial gut bacteria.
During times of celiac disease — you know, a bout of diarrhea where all the good gut bacteria are being flushed out of the system — the appendix is sort of this blind tube with a very narrow diameter and a narrow lumen, so the good bacteria doesn’t get flushed out of the appendix. The idea is that they are safe during this time of celiac disease and can then come out of the appendix and recolonize these good bacteria in the rest of the intestines.
So the appendix helps us in two ways, both within the gut – it helps fight off invading pathogens – but also to repopulate the gut with these beneficial bacteria after digestive issues.
Why do some people get appendicitis?
Appendicitis occurs mostly in industrialized countries of the world, areas where the fiber content of the diet tends to be low. So, one hypothesis is that with low fiber content, small pieces of digested food are more likely to stick (inside) the appendix and cut off its blood supply and cause this inflammation.
The other hypothesis that doesn’t seem quite as plausible these days is related to an old idea called the hygiene hypothesis. The idea is that these days we’re so over-sterilized, with all the antibacterials we have and all the antibiotics we’re taking, that our immune systems aren’t developing properly because they’re not being exposed to the full range of pathogens that we might be exposed to. Unlike that. Therefore, the immune system overreacts and panics. Because the appendix contains a lot of immune tissue, it is one of the areas where this appears.
Could this new understanding lead to new treatments?
I think there are some promising treatments out there. People are looking for antibiotics and other ways to treat appendicitis without completely removing it, due to accumulating evidence, which actually suggests that it is beneficial for your health to have an appendix. Studies have shown that infections with the nasty, pesky C-diff bacteria tend to be higher in people who have had their appendix removed.
So there are health benefits to retaining our appendix – in an ideal world, we’d have a future where we wouldn’t always have to remove it.
What have you gained from studying this “strange little organ”?
I think this study showed me the importance of looking at small anatomical details. Anatomy is just the study of the body, so you might think it’s a dead science. You might think that we know everything about the body, especially the human body.
But it turns out that there are actually a lot of subtle anatomical differences, functions and adaptations that have not been fully realized. So doing only descriptive studies of exotic animals that have not been described before or looking at small parts of our bodies that are not well documented is completely worthwhile.