Mechanical factors in the development of the vascular bed.

During embryonic development, blood flow is needed not only to nourish the developing embryo but is also important for shaping the vascular network such that it becomes hemodynamically efficient. The first blood vessels form a network called the capillary plexus. After the onset of blood flow, the capillary plexus remodel into a more hierarchical tree-shaped network. Mechanical forces created by blood flow are required for remodelling to occur and these forces are believed to induce a maturation of the blood vessels that stabilizes the growing vascular network. The role of mechanical force has been extensively studied in the mature cardiovascular system. Though the events induced by blood flow during development are thought to be similar to what occurs in the adult, there are several important differences between the embryo and the adult. We therefore discuss what is known about the role of mechanical forces in vascular remodelling from the adult cardiovascular system and highlight how embryonic development differs from the adult. We consider the role of blood flow in altering branching morphology, arterial-venous identity and the formation of the blood vessel wall during early vascular development.