ABSTRACT
Blood vessels are primarily composed of two cell types: endothelial cells, lining the inside and smooth muscle cells, covering the outside. While angiogenesis research has generally been focused on these two vascular cell types, recent evidence indicates that the bone marrow may also contribute to this process, both in the embryo and the adult. Following commitment to the endothelial lineage, marrow-derived angioblasts assemble into a primitive vascular plexus of veins and arteries, a process called vasculogenesis. This primitive vasculature is subsequently refined into a functional network by angiogenesis (vascular sprouting from preexisting vessels, vascular fusion and intussusception) and by remodeling and muscularization (arteriogenesis) of newly formed vessels. 1
