Discovery of previously unknown blood vessel system in bones.
Although bones are hard ossified organs, they have a dense network of blood vessels inside them where bone marrow is located. as well as on their outer surface covered by the periosteum. While it is known that fresh blood is transported into organs around the body via arteries with veins transporting the used blood back out again, however, the precise structure of the same closed bloodstream in long bones is still unclear. Now a study from researchers led by Universität Duisburg-Essen identifies a previously unknown network of very fine blood vessels which connects bone marrow directly with the blood supply of the periosteum. The team state they found blood vessels in the bones of mice which traverse perpendicularly across the entire length of the compact bone, the so-called cortical bone, and have dubbed them ‘trans-cortical vessels’ (TCVs) for this reason. The opensource study is published in the journal Nature Metabolism.
Previous studies show that closed circulatory blood systems underlie the function of vertebrate organs, however, in long bones their structure is unclear although they constitute the exit route for bone marrow neutrophils. Previous concepts have only described a few single arterial canals and two venous canals in bones which is completely inaccurate and does not reflect the actual situation at all. The current study investigates the vascular system of long bones in mice to understand neutrophil migration from bone marrow.
The current study images the distribution of blood vessels in murine long bones treated with a chemical to make them transparent using light-sheet fluorescence microscopy and X-ray microscopy. Results show hundreds of capillaries along the entire bone shaft which cross the cortical bone perpendicularly and form a direct connection between the endosteal and periosteal circulations. Data findings show that the majority of both arterial and venous blood flows through this newly discovered system of vessels which means the system is a central component for supplying bones with oxygen and nutrients.
The lab state the newly-discovered system of vessels is used by the immune cells in bone marrow to reach the bloodstream, and in the case of inflammatory diseases such as arthritis, it is especially important that immune cells reach the source of the inflammation quick. They conclude that in long bones, TCVs form the mainstay of blood circulation and constitute the missing link in the search for a fully functional closed circulatory system.
The team surmise they have identified a previously unknown blood vessel system in bones which helps immune cells to quickly reach sources of inflammation. For the future, the researchers state they plan to investigate the role of TCVs for normal bone remodelling and in conditions such as osteoporosis or tumours which metastasise in bones.