970x125
Not many people would bet on new human anatomy being discovered in the twenty-first century. But the last couple of decades have been a little wild.
This is a story about the discovery of two new anatomical features, one small and one large, and how they turned out to be intertwined. As a bonus, they also play a role in the gut-brain axis.
Holding Organs in Place with Connective Tissue
Our organs are tacked in place by a patchwork of tissues. It is a webwork of tough collagen and elastin fibers suffused with hyaluronic acid, which attracts water to create a gel. That gel ebbs and flows, accompanied by a smattering of cells, microbes, and molecules.
Recently, a landmark study by Dr. Neil Theise and colleagues showed that all these patches are connected into a single continuous, body-wide tissue. If it were an organ, it would be the largest one in the body, demoting the skin to close second. But most researchers, including Dr. Theise, consider it to be a mere tissue, which is a little disappointing.
It is called the interstitium. The interstitium isn’t just large, it is all-encompassing. As well as your organs, all your blood vessels and nerves run through it.
The Role of the Interstitium
When the gut is inflamed, it can become leaky, allowing toxins and microbes to break through the delicate gut lining. When they do, they may find themselves in the interstitium, migrating through the entire body, typically pursued by immune cells. If this cat-and-mouse game drifts past the brain, it can set the stage for brain inflammation.
Unlike the circulatory system, there is no heart to pump the interstitial fluid. But that doesn’t mean the heart isn’t involved: the rhythmic pulsing of arteries gently pushes the hyaluronic acid around. And, since it surrounds your muscles, with every movement you squeeze your interstitium like a sponge, pumping fluid everywhere.
Along with the vagus nerve and the bloodstream, the interstitium provides a whole new superhighway for gut microbes and their metabolites to affect the brain. The researchers noted that “the interstitium is a route for microbiome signaling.” I wrote to Dr. Theise to ask him about the microbial connection. He replied, “I’ve been waiting for someone, anyone, to take note that we keep mentioning this in our papers.”
Microbial signals can be positive or negative. Are interstitial microbes pathogens, or have some of them set up a healthy community? Theise says, “it is unclear. I suspect it is largely sterile, but bacterial products or fragments traffic through it routinely.”
Still, he says, “the interstitium certainly is a missing piece of any pathway for microbial signaling.” That’s because, for any microbes or toxins to enter the bloodstream or affect a nerve, they must first pass through the interstitium to get there.
Understanding the Lymphatic and Glymphatic Systems
Blood vessels are not the only circulatory system in the body. There is also lymph. It doesn’t have a pump, but it circulates due to one-way valves throughout the system. As your body goes about its metabolic business, it produces a lot of waste products. These are sucked up by the lymphatic system which ferries them to the blood and then to the kidneys for removal. But the lymphatic system doesn’t seem to extend to the brain. The removal of brain waste has been a long-standing mystery.
That is, until 2013 when Danish neuroscientist Maiken Nedergaard discovered small channels alongside veins in the brain that do the job. She called it the glymphatic system. Among other things, it is in charge of eliminating the amyloid molecules that build up in Alzheimer’s disease.
I asked Theise if there was a connection between the interstitium and the glymphatic system. He said, “Yes, and a lot of folks are thinking it is a primary, or the primary drainage pathway of the glymphatic system.”
Gut-Brain Axis Essential Reads
Could this be a pathway for microbes to communicate with the brain? Theise says, “Yes. A continuous interstitial pathway means that gut-derived signals might find a more direct anatomical ‘back door’ into the central nervous system’s fluid compartments.”
Piezoelectric Properties of Connective Tissue and Chinese Medicine
There is another interesting angle to this research: the network of elastin and collagen is unexpectedly piezoelectric, meaning that if you press it or bend it, it will generate electricity. This is intriguing, because electrical signals generated by piezoelectric materials may play a role in processes such as bone healing, nerve regeneration and skin repair.
This squishy electric network bears an uncanny resemblance to the Chinese notion of Qi, the circulating life force. Could the piezoelectric fibers explain the workings of acupressure or acupuncture? This is something that researchers are starting to explore.
If so, the gut-brain axis, via the interstitium, may yield to some ancient leverage, and give us new tools to manage our moods, memory, and cognition. Not bad for an anatomical feature we only recently discovered.
