We often think of bone as a structural solid, especially for its hard outer layer, called cortical bone.
But a new discovery of never-before-hidden passages that pass through these rigid organs in both animals and humans can lead to rethinking the structure and function of basic skeletal anatomy.
In a new study, researchers in Germany report a previously discovered undetected network of fine blood vessels that act as a secret tunnel system inside the bones, helping blood and immune cells to spread efficiently and quickly throughout the body.
Elon Musk would probably approve.
"It is indeed unexpected to find a new central anatomical structure that is not described in any 21st century textbook," explains Mathias Güntzer, a molecular immunologist at the University of Duisburg-Essen.
These mini-channels, called trans-cortical vessels, may be new to science, but they help explain how emergency drug infusions, the first on the battlefield, can quickly revive the wounded soldiers.
In such emergency situations, medics do not always have the time or opportunity to find or gain access to veins, by resorting to drug injections directly into the bone marrow.
"Despite the accumulation of evidence of complex blood supply in the bones, the molecular mechanisms and anatomy that underlie these rapid changes in bone marrow cells and fluids in the circulation remain elusive," the new study explains.
The basis for this mechanism is now bare, as it was previously noticed a few years ago. Gunzer studied fluorescence stained blood cells in mice and observed them under the microscope, apparently going through what was supposed to be hard bone.
Unable to find anything in the medical literature to explain the phenomenon, he invented a new research project to explore what is happening.
In the new study, Gunzer's team used a chemical called ethyl cinnamate in tibial mice (bone bones) to "clear" the bones, making them transparent.
Then, using a combination of fluorescence microscopy (LSFM) and X-ray microscopy, they were able to detect for the first time several hundred of these tiny TCVs passing through the cortical layer of the bones.
According to the researchers, mouse tibia may contain more than 1000 of these small capillaries, and amazingly enough, the team says that over 80% of the arterial and 59% of the venous blood passes through the canals.
This is a lot of blood flow to something the scientists did not even know about.
"I have never seen such vessels," said RALF Mueller of the Swiss Federal Institute of Technology, who was not involved in the study.
"But we have never looked that way, so it's a surprise for me … it will surely need a little repeat in other labs."
When the team explored human anatomy by portraying the bone of a volunteer bone (Gunzer himself), they found evidence of the same type of TCV structures, although they were thicker and the researchers admit that more work is needed to confirm their accurate function.
Regarding how these hidden passages faded from our note so far, the team says the breakthrough is related to technological advances in rendering, but they admit they are even surprised by the unexpected result.
"There is still a lot of crazy things to learn about human anatomy," said Gunzer New Scientist,
"We found blood vessels in a new place we did not know before.
The discovery, reminiscent of another secret tunnel system in the skull, revealed by a Harvard study last year, could lead to any new medical findings for the study of inflammatory diseases, tissue damage, cell migration, or simply understanding how blood is flowing.
"Since key bone pathologies are linked to changes in the TCV system," the authors write in his article, "entirely new research capabilities can be provided that further characterize the role of TCVs in skeletal biology and disease."
The findings are reported in Metabolism of nature,