FIGURE 1.

Bone marrow vascular network. Schematic representation of a femur section and the vascular component of the corresponding bone marrow. Trabecular bone, a type of porous bone with high turnover also called cancellous or spongy bone is mainly found at the ends of the femur in the epiphysis and metaphysis regions. The endosteum is known as the bone marrow region adjacent to bone. Columnar blood vessels corresponding to type H endothelium and arterioles are mainly found in the metaphysis, whereas sinusoidal vessels corresponding to type L endothelium are predominantly located in the diaphysis. Nutrients, oxygen and other factors enter the bone marrow mainly through the central artery, which branches into arterioles and then through transitional vessels into a vast network of sinusoids, fenestrated vessels where the exchange of cells and factors takes place. Sinusoids converge into the central sinus allowing for the exit of waste products from the BM through the venous circulation. Sca-1, stem cell antigen-1; PDPN, podoplanin; VEGFR3, vascular endothelial growth factor receptor 3; Emcn, endomucin.