What are the steps that endothelial cells take to form new blood vessels?

The main steps that endothelial cells take to form new blood vessels include: enzymatic degradation of capillary basement, endothelial cell proliferation, migration of endothelial cells, tubulogenesis, vessel fusion, pericyte stabilization and vessel pruning. 

1. In the early stages of angiogenesis (in response to VEGF induced by wounding and ischemia) the vascular basement is degraded by proteases. 
2. Following the disruption of the basement membrane, endothelial stalk cells then proliferate, migrate, and coalesce to form a lumen within a series of stalk cells. 
3. The stalk cells become the trunk of the newly formed capillary. 
4. Tubes must then be formed with lumens in order to carry out the flow of blood. This process is known as tubulogenesis. 
5. Next, when the tip cells of two or greater capillary sprouts come together at the source of VEGF-A secretion, the tip cells fuse together producing a continuous lumen in which oxygenated blood can flow through. 
6. When the tissues begin to receive adequate amounts of oxygen, VEGF-A levels return to near normal. 
7. The maturation and stabilization of the capillary requires pericytes and deposition of ECM along with shear stress and other signals.