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. 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 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 connecting bone marrow directly to the blood supply of the periosteum. The team states they found blood vessels in the bones of mice traversing 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 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. Recent inaccurate concepts have only described a few single arterial canals and two venous canals in bones. 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 crossing the cortical bone perpendicularly and forming a direct connection between the endosteal and periosteal circulations. Data findings show the majority of both arterial and venous blood flows through this newly discovered system of vessels suggesting the system is a central component for supplying bones with oxygen and nutrients.
The lab states the newly-discovered system of vessels is used by the immune cells in the bone marrow to reach the bloodstream, and in the case of inflammatory diseases such as arthritis, it is especially important for immune cells to reach the source of the inflammation quickly. They conclude 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 surmises they have identified a previously unknown blood vessel system in bones helping 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 remodeling and in conditions such as osteoporosis or tumors metastasizing in bones.
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