Science & Technology

Scientists Just Discovered a Huge New Organ in the Human Body

The state of scientific knowledge doesn't always make much sense. We know more about the surface of Mars than we do about the bottom of our own ocean, for example, and we've figured out almost every bizarre quantum force but somehow still fail at explaining gravity. Tuesday's discovery puts another head scratcher on that list: we're still discovering new human organs. Meet your interstitium. It's everywhere inside you, and it could be the explanation for medical mysteries ranging from why skin wrinkles to why cancer spreads.

The interstitium is a large network of fluid-filled spaces that surround your lungs, digestive tract, blood vessels, and many other organs. This diagram shows how those spaces are supported by collagen bundles and lined with a layer of cells.

A Series of Tubes

As often happens when scientists discover something that was there the whole time, this discovery came down to a boost in technology. In 2015, Dr. David Carr-Locke and Dr. Petros Benias were using new imaging technology called probe-based confocal laser endomicroscopy, or pCLE, to examine a patient's bile duct for cancer. This device combines a tiny snake-like camera called an endoscope with laser/detector combo, which shines light on tissues and analyzes the fluorescent patterns of the reflections. That allows researchers to get a microscopic view of living tissue without having to take a sample.

With the help of pCLE, the doctors noticed something strange: there was a series of interconnected, fluid-filled cavities in the surrounding tissue layer that didn't match anything they were familiar with. See, we had always thought that the digestive tract, lungs, muscles, and other organs were surrounded by a dense wall of collagen — the same strong, fibrous stuff that makes up your ligaments and tendons. But this was different. They sent the tissue to a pathologist, who sliced them into thin sections so they could be viewed on a slide under a microscope — but when they looked at the slide, the cavities had disappeared.

The doctors recruited a research team and used the same new technology on the bile ducts of cancer patients who were having them removed. Again, pCLE showed them that there was a network of fluid-filled spaces in the connective tissue around the organs. But this time, they rapidly froze the samples before cutting them, then looked at each one under a microscope. Ah ha! There were the fluid-filled cavities, clear as day. It turns out that when the pathologist — or pretty much any scientist trying to look at these types of tissues under a microscope until now — sliced the tissues, the fluid drained out and collapsed the spaces, making them effectively invisible to the microscope.

Once they saw these spaces, it was easy to detect them throughout the body. There they were: in the fascia between muscles, around the veins and arteries, below the skin's surface, lining the digestive tract, surrounding the lungs, and cushioning the urinary system — basically anything that needs a little shock absorption as you go about your day. On March 27, 2018, the researchers announced that they'd named this vast, interconnected network of fluid-filled compartments the interstitium, for the interstitial fluid that fills it.

What It All Means

Medical science has known about interstitial fluid for a long time. It makes up about a third of the water inside your body, with another half filling your cells. But this team is the first to actually define the network that holds this interstitial fluid as an organ in its own right. That's unofficial at this point — according to LiveScience, enough researchers need to study it in order to reach a consensus about its true definition before it officially becomes an organ.

But regardless of what it's called, the discovery that there's a highway of moving fluid inside you could unlock a few mysteries. For one thing, it could explain why cancer is more likely to spread to the lymph nodes once it has entered one of these spaces. The interstitium is the source of lymph, a fluid that contains infection-fighting immune cells, and that drains into the lymphatic system. A less life-threatening function of the new organ could be in aging: the cells and collagen bundles in the interstitium break down over the years, which could lead to wrinkled skin and stiff joints.

So welcome your new organ to the party! It's been here all along, but now it has a name.

Science doesn't always go as planned. "The Accidental Scientist" by Graeme Donald shows how chance, luck, and error played a role in some of the most famous discoveries and advancements in history. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.

Written by Ashley Hamer March 28, 2018

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