Scientists have discovered a hidden network within our bones, a maze of tiny blood vessels that’s never been seen before. The findings are published in the journal Nature Metabolism.
“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,” said Professor Matthias Gunzer, who led the research at the University of Duisburg-Essen in Germany, in a statement.
Scientists have known for some time that bones have an efficient blood system that allows blood cells, as well as immune cells made in the bone marrow, to quickly migrate into general circulation, but this is the first time we've actually managed to see it. In emergency situations, when a vein can't quickly be accessed, paramedics inject drugs directly into a person's bone marrow. Now we know why that works so well.
We've already seen other kinds of blood vessels in the bone, like those at the center in the bone marrow and at the surface in the periosteum – a layer of connective tissue surrounding the bones. But the new vessels appear to traverse directly through long bones (long, cylindrical, marrow-containing bones like arm and leg bones), at an angle of 90 degrees from the bone’s long axis.
“Like any other organ, bones also need a closed circulatory loop (CCL) to function properly. This delivers fresh blood via arteries into the bone and transports used blood out via veins,” explained first author Dr Anika Grüneboom. “How exactly the CCL of long bones functions was not totally clear until now.”
The researchers first identified the new vessels – referred to as trans cortical vessels – in mice. Using a chemical called ethyl cinnamate, they were able to make mouse leg bones transparent. They stained blood cells red and green and when they looked through the microscope, they could see these colored cells passing through what appeared to be solid bone. In a single mouse tibia (lower leg bone) the team found roughly 1,000 trans cortical vessels.
They also discovered that the majority of the blood in long bones passes through this network of vessels – 80 percent of arterial blood and 59 percent of venous blood to be precise.
The researchers also identified the new vessels in small samples of human thigh bones – there weren’t as many, but they were still there. Professor Gunzer himself volunteered as a test subject, spending six hours in an imaging machine while his lower leg was scanned in detail. Once again, the researchers spotted their newly identified network of vessels.
It seems bizarre that an entire type of blood vessel could go unnoticed for so long, but the discovery is likely thanks to technological advances in certain imaging techniques that made the structures visible.
The team notes that future research is needed to work out the exact role that trans cortical vessels play within the body, and whether they're involved in certain bone diseases, such as rheumatoid arthritis, osteoporosis, and bone tumors.