New study finds blood vessels passing through ‘solid’ bone

As a species, humans understand a lot about their own physiology. Right down to the microscopic scale, we can describe systems and components that affect our health and wellbeing. And yet, even with all of our knowledge and the amazing rate of current medical advances, we are still unearthing completely novel elements of human anatomy.

In March last year, an entirely new organ was found called the interstitium (a system of fluid-filled compartments throughout the body). And now, in a study published in Nature Metabolism, a novel system of blood vessels has been uncovered. As incredible as this discovery is, the location is even more bizarre – they pass through seemingly solid bone.

Professor Matthias Gunzer’s research group at the University of Duisberg-Essen in Germany were staining red blood cells red and green to investigate their origin. These cells, along with immune cell types, are produced in the bone marrow and then enter into the bloodstream, so their analysis started at the beginning of their life cycle in a mouse leg bone. When they saw the coloured blobs moving through supposedly solid bone, they knew that further investigation was required.

Previously, it was thought that there were a couple of blood vessels entering the bone at either end or halfway along. These would supply a small amount of blood and allow for the various functions of the marrow to occur. But these new blood vessels, called transcortical vessels (TCVs), far surpass a small blood supply. In one match-stick-sized mouse tibia (the lower leg bone), the researchers could see roughly 1,000 TCVs.

But the German research group knew that looking in mice was not enough. Scientists had guessed that humans must have a connection passing from the marrow in the bones to the blood, but it had never been seen. We could never fully explain how paramedics could rapidly administer drugs to a patient through an injection into their bone marrow if a vein couldn’t be found. This method has been around for a very long time, first being pioneered on battlefields over seventy years ago. But we never knew how it worked. Therefore, to investigate the presence of TCVs in humans, Professor Gunzer himself offered to play research subject. After six hours in an imaging machine, there was success – TCVs could be seen passing in and out of his bones.

Although it has not yet been demonstrated that human immune cells are using the TCV route, the speculation about possible implications for medicine has become intense. Not only having a potential role in direct bone diseases such as osteoporosis and bone tumours, but conditions that have a basis in the immune system could be reliant upon these TCVs. The key example of this is rheumatoid arthritis, a disease that sees the immune system attack the joints and causes severe inflammation and swelling.

In a statement, Professor Gunzer said: “It is really unexpected being able to find a new and central anatomical structure that has not been described in any textbook in the 21st century.” While it is debatable if new discoveries, such as TCVs, are possible due to advances in technology or medical knowledge, it is clear that we don’t know anywhere near as much as we thought we did. We can only speculate how important they will transpire to be but for now, we can add an entirely new blood vessel system to our textbooks.

 

Image credit: University of Liverpool Faculty of Health & Life Sciences’ Photostream via Flickr

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