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And then there were 80: The discovery of a new human organ

As a biologist, one of my most favorite things to talk about with people is how little we know about the human body (especially the brain). I think our ignorance about our own bodies really underlines how much mystery is still out there…or I guess in here? As technology advances, our exploratory abilities improve, allowing us to observe new and diverse things, like a new organ within the skin layers, for example.

We typically think of human skin as the resilient outer layer of our bodies. Skin (or dermis) makes up quite a bit of our bodies on the inside as well. Typically, we think of skin as a densely packed, layered structure of cells and squishy, stretchy collagen. (Yes, the stuff people put in lips, and the stuff that wears away inside joints when someone has arthritis.) There’s also fluid that can surround the cells within the dermis–which is usually either lymph fluid, blood plasma, or interstitial fluid. Researchers and clinicians at Mount Sinai hospital in New York City discovered that our perception of skin is inaccurate. There is really a series of tubes that sits within the skin, that helps an interstitial fluid move throughout the body.

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The old-school schematic of dermal layers.

Dr. Petros Benias and his homiest of homies discovered a reticular pattern in a chunk of bile duct they were biopsying. Intrigued, they froze the tiny piece of tissue, and continued to look at it outside of the body (or ex vivo, if you fancy). They noticed that that spidery, wandering pattern was preserved, and further exploration showed they were really a series of tubes! They found the same tubing in multiple places in the body, including around the gut and from the external skin, and suggest that this type of network found near organs that go through cycles of expansion and contraction, such as the bladder, stomach, intestines, lungs, and heart.

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The updated schematic of dermal layers. So juicy.

This system, called, the submucosal interstitial, is comprised of collagenous bundles  that surrounded an interstitial fluid, and are bounded by weird-looking cells that don’t resemble skin cells. They found the fluid to be pre-lymphatic (lymph fluid is produced by the lymph nodes, and generally does a bunch of immune system jobs), finding immune proteins in the cells and some of the fluid in the tissue. These proteins include CD34, labeled in the image above.

Dr. Benias and his crew also looked at some cancerous growths, mostly second phase, and found that there was a lot of cancerous development in this newly-found interstitial fluid. This discovery lead the researchers to think that perhaps this new tubular structure has something to do with how cancer moves through tissue. Interesting, no?

So how come we didn’t know about this network before? The researchers not only prepared these tubular tissues with a flash-freezing procedure, but also used the more traditional fixing of tissues, and compared the results. It turns out, if you don’t freeze the tissue immediately, the tubes collapse, and all you see is the collagen structure, and NOT the tubes! Crazy!

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Fixed tissue showing the interstitial tube network (left, in blue), with the tubular areas starred. The two images on the right show traditional preparations of the same tissue, with no tubes seen, or collapsed tubes (arrows).

So what’s next? The researchers posited that the fluid in the interstitium is probably propelled by some sort of pumping mechanism, and suggest that we revisit how fluids move around these expanding and contracting organs, to see if they contribute at all to movement in the newly found organ. It could be that problems with fluid flow in the interstitium could contribute, develop or spread diseases, like cancer.


More reading!

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Think it’s been a while since we discovered an organ? Guess again! Back in early 2017, a new organ of the digestive tract was discovered!

Primary literature 

 

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