VEGF can affect the process of embryonic angiogenesis in addition to its roles in vasculogenesis described previously. The effect of VEGF on angiogenesis has been examined in the mouse eye, where the retinal vasculature expands by sprouting as the retina grows . The vascular sprout contains two types of endothelial cells: tip cells and stalk cells, which can be distinguished by differences in gene expression and morphology . Filopodia of tip cells direct cell migration by sensing a gradient of VEGF, while stalk cells respond to VEGF by proliferation. VEGF induces filopodia to extend from tip cells, which are guided toward VEGF sources. VEGF antagonists inhibit these activities. This is similar to the protrusive activity of endothelial cells in the developing quail embryo, as disruption of VEGF gradients inhibits protrusive activity and migration of sprouting tip cells.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.