The initiation of blood flow and flow induced events in early vascular development

► Blood flow begins after the formation of a vascular loop, the initiation of cardiac contraction and the entry of erythrocytes. ► Flow patterns in the embryo differ from the adult, with much lower levels of shear stress and the presence of retrograde flow. ► Mechanical signals from flow are required for vascular morphogenesis; including aortic arch formation and production of HSCs.