Nobody knows what organs are!

I mean, you probably think you know what organs are. Your brain is an organ.

Your lungs are organs. They’re structured blobs made of different kinds of cells, all working together to do a unique job in your body. Like, your lungs do the job of taking in oxygen.

But, as it turns out, those characteristics don’t apply to all organs. Or they might not, depending on who you ask. Experts don’t agree on exactly what an organ is, or how many you have.

Around the end of the 2010s, there was a surge in publications arguing for the promotion of certain body parts to organs. But maybe it’s okay that there’s no consensus. Simply having these conversations can make researchers pay more attention to overlooked body parts.

And by paying attention to them, we sometimes discover the critical roles they play in disease. [♪ INTRO] Imagine the following: After more radiotherapy than anyone would hope to receive in a lifetime, you’ve just received the good news from your oncologist: you’re in remission from the cancer in your neck. It’s a bright, sunny day and you’re heading out for your lunch break. You unwrap your sandwich and dig in.

But you can’t manage to get the bite down. Dysphagia, or trouble swallowing, turns one of life’s great joys into a scary experience. While you know there’s something wrong with your body, you might not have the words to describe where in your body the problem lies.

And words are important, because they can help you to take action, like clearly expressing to your doctor what you’re struggling with. If you’re unable to swallow those bits of delicious sandwich, the trouble could be your tubarial glands. They’re small clusters of cells in the center of your head, under your brain, between your nose and your spine, which probably weren’t protected while you were undergoing radiotherapy.

And you didn’t think anything of it, because what are the odds that you’ve even heard of tubarial glands? While doctors have known about them since 1837, they haven’t been seen as particularly important. Some researchers think they’re part of a larger gland system, and not a standalone, independent structure.

But a study published in 2020 reported what happens to those glands when they’re exposed to radiation: dysphagia. See, tubarial glands are thought to help lubricate the upper throat area. So if they get damaged, swallowing can become difficult.

Because of their association with specific disorders like dysphagia, the authors of this publication suggested tubarial glands should be classified as “organs at risk.” That means that they would need to be protected from the toxicity of radiotherapy whenever possible. But calling them organs would require redefining our idea of what an organ is. While their status as independent from other, similar glands is debatable, the 2020 study did confirm that the tubarial glands serve a function in regulating dysphagia.

So they may not be traditional organs, but by calling them organs, we could help keep some cancer patients from experiencing additional difficulties. And we come another step closer to understanding how dysphagia works. Okay, maybe extending the definition of organ to include a gland or two doesn’t seem too out there if it’s for a good cause.

But some body parts that could benefit from a little extra care and attention are a bigger step away from what we classically think of as organs… like the mesentery That’s a structure that runs alongside the intestines and generally influences how well your guts work. Similar to the tubarial glands, the mesentery isn’t a recent discovery. People have been describing it since at least the 1500s.

Some of the earliest recorded descriptions of the mesentery were made by Leonardo da Vinci, who suggested that it was one continuous unit. But it’s all twisted up in the intestines, so you can’t really tell that the different segments are connected unless you pull it out in a specific orientation. So the depiction that prevailed instead of Da Vinci’s was a fragmented mesentery proposed by a professor at the Royal College of Surgeons at the London Hospital named Frederick Treves in 1885.

Treves considered it to be three separate units, each connected to a different part of the digestive tract. Despite that predominantly accepted idea, surgeons seemed to approach the mesentery differently when treating colon cancer. They would detach the entire thing for the best results rather than just the section that anatomists described as attached to the colon.

Basically, the debate about what the mesentery even looks like has been going on for decades, if not centuries. That made some people hesitant to consider it a traditional organ if it’s not one distinct structure. But today, it’s fairly well accepted that the mesentery is all one thing, bringing it closer to organ-dom.

It has even been proposed as a critical player in Crohn’s disease. That’s an inflammatory bowel disease that makes things many of us do everyday without thinking about them, like pooping, pretty crappy. When the mesentery isn’t working properly, it gets rigid and inflamed, which might be part of how Crohn’s disease works.

And if treating the mesentery like an organ helps us figure out how it inflames your guts, then by all means, let’s treat it like an organ. By now, you might be on board with calling connected blobs of tissue like the tubarial glands or the mesentery “organs,” but this last body part could be where you draw the line. Because it’s not so much a body part as it is multiple spaces between your body parts.

I’m talking about the interstitium. While researchers have known about the interstitium for decades, they didn’t really give it a second thought, because space between parts does sound pretty inconsequential. But in 2018, we learned it’s really a bunch of connected fluid-filled sacs.

And it’s in that distinction where we discovered the interstitium’s purpose. It can act as a shock absorber, protecting all of your other insides if you get jostled around too vigorously. Which is an important job.

I like my squishy bits to be protected. But being a malleable fluid-filled space also means cells might have an easier time traveling through the interstitium. And that’s not always a good thing.

If you have cancer, the interstitium could become a little tumor highway. So while it’s reasonable to argue a bunch of disconnected support sacs aren’t an organ, they’re worth paying some extra attention to. Body parts like these might not act like your brain, heart, or spleen, but they’re crucial to your health in other ways.

If we expand our idea of what an organ is, that could help us learn things about ourselves we never would have with the old rigid definitions. And hey. Maybe it’s okay that no one can say for sure exactly how many organs you have.

There’s a lot we aren’t sure about in the universe. But sometimes, we have the opportunity to learn and change that. Years ago, we weren’t sure what the Moon was made of.

But thanks to the rocket featured in this month’s SciShow Space Pin of the Month, we now know there’s a bunch of iron in there. Some of it’s solid, some of it’s liquid, and some of it’s molten. And it took crashing part of a rocket into the Moon to find out!

To learn more about that story, you can watch the SciShow video all about S-IVB. And to show your appreciation for the sacrifice of that rocket stage, and for the people who make SciShow happen, you can get your own S-IVB pin at DFTBA.com/SciShow. We can make the universe more knowable together! [♪ OUTRO]