In its process, there will be migration of endothelial cells, degradation of the basement membrane of the venule to move to an angiogenic stimulus, and alignment of endothelial cells to create a sprout while a curvature is formed in each endothelial cell to form a lumen in the vessel. The proliferation of the endothelial cells, increase of length of the sprout will form two hollow sprouts that join at their tips and create a loop and allow blood to flow. Pericytes will line the base of the loops and growth of new sprouts can occur. The process regarding the last steps of angiogenesis even if not clearly understood is thought to be guided by tip cells, specialized cells at the front of the sprout (Bergers & Benjamin, 2003). Gerhardt et. al. (2003) conducted a study on the angiogenesis in the retina of mice. The results found that retinal vessels grow in expanding circles and the sprouts were supported by proliferative stalk cells and guided by specialized tip cells. It revealed that the tip cells grow by extension along filopodia and that they are highly polarized with a uniquely responsive VEGF-A isoform. The filopodia are created by astrocytes and guides the tip cells by noticing the gradients of the VEGF-A. The stalk cells are also responsive to VEGF-A to its absolute concentration but not its gradient (Gerhardt, et.al,
In its process, there will be migration of endothelial cells, degradation of the basement membrane of the venule to move to an angiogenic stimulus, and alignment of endothelial cells to create a sprout while a curvature is formed in each endothelial cell to form a lumen in the vessel. The proliferation of the endothelial cells, increase of length of the sprout will form two hollow sprouts that join at their tips and create a loop and allow blood to flow. Pericytes will line the base of the loops and growth of new sprouts can occur. The process regarding the last steps of angiogenesis even if not clearly understood is thought to be guided by tip cells, specialized cells at the front of the sprout (Bergers & Benjamin, 2003). Gerhardt et. al. (2003) conducted a study on the angiogenesis in the retina of mice. The results found that retinal vessels grow in expanding circles and the sprouts were supported by proliferative stalk cells and guided by specialized tip cells. It revealed that the tip cells grow by extension along filopodia and that they are highly polarized with a uniquely responsive VEGF-A isoform. The filopodia are created by astrocytes and guides the tip cells by noticing the gradients of the VEGF-A. The stalk cells are also responsive to VEGF-A to its absolute concentration but not its gradient (Gerhardt, et.al,