I know, it just popped up overnight!

I don't think I felt mine grow in, did you?

No, I'm just kidding, this structure was actually always there, but we're only just

now recognizing what it is and how it really works.

And it's a pretty big deal--it changes the way we see not only our bodies and how they

work, but also a whole host of important diseases.

Does that really make it a new organ, though?

An organ is a group of tissues that perform a specific function.

There's a thing in our body called the interstitium, also known as the interstitial space*, which

is a layer of tissue we've known about for a long time.

It sits beneath our skin, surrounding all of our organs and arteries and veins and muscles,

blanketing them on the inside just like our skin covers our body on the outside.

But a few months ago, researchers were looking at a patient's bile duct for signs of cancer

when they saw something in the interstitium that didn't match up with any known human

anatomy.

See, the way we typically study human tissues in a lab is to take an extremely thin slice

and look at it on a slide under a microscope, maybe dying it different colors to enable

us to see certain structures.

But doing this removes all the fluid from that tissue sample.

And this means we've been missing something big.

Up until now, we've thought that the interstitium was just plain ol' connective tissue.

We have connective tissue all over our bodies, connecting bones to one another, connecting

our muscles to our bones, and generally just holding us together.

It's important, but pretty ubiquitous and typically not very specialized.

But these researchers saw something new because they were looking at tissue samples in a new

way.

Using a technique called confocal laser endomicroscopy, they could see the TRUE nature of the interstitium..this

visualization method uses a low-powered laser to scan an area of the body and create a digital

3D reconstruction.

Using this technique, researchers could now observe a whole network of fluid-filled sacs--structures

that got drained and therefore essentially disappeared when we'd looked at interstitium

samples with the more traditional slice and 'scope method.

We've now observed that the interstitium is actually a complex network of interconnected

fluid-filled compartments, supported by connective tissue proteins like collagen and elastin.

It may act as a shock absorber, twisting and bending with our bodies as we move, keeping

our organs in place and keeping them from tearing or otherwise flopping or floating

about in our bodies.

Perhaps even more importantly, the fluid in the interstitium is connected to our lymphatic

system, draining to our lymph nodes, and it may actually be a source of lymph.

Which is HUGE because lymphatic fluid is an essential part of our immune system, carrying

cells that fight infection...but it also plays a major role in the spread of cancer.

When cancer metastasizes, it spreads from its tissue of origin to other parts of the

body through the blood or the lymph.

So understanding the interstitium as a new key player in the lymphatic system could give

us a better understanding of cancer, and why and how it spreads.

But.

The million dollar question.

Is the interstitium truly an organ?

No.

Not yet, at least.

For it to be classified as such it'll take lots of follow-up research and verification.

I mean the mesentary, which we talked about last year, still isn't an official organ,

so it takes some serious doing to get on that list.

Really, calling something an organ is mostly a semantic distinction.

It could help direct research toward this structure, but the significance of this work

is pretty independent of whether call the interstitium a new organ or not.

This study not only revealed brand new information about the way our bodies work, but also made

us call into question the way we've been looking at them.

And last but not least, this discovery has sparked conversation once again about what

organs are and how we classify them and what counts as one...a discussion that's constantly

evolving in the scientific field.

I love that science is always changing and learning from itself.

What else do you think we haven't known about our bodies this whole time?

Let us know in the comments, and check out Sam's video here to learn about a part of

the brain that's been hiding from us.

Thanks for watching!