Angiogenesis is the process of generating new capillary blood vessels.
Angiogenesis is fundamental to healing, reproduction, embryonic development.
Both processes are mediated by paracrine growth factors. The paracrine factors that regulate angiogenesis accomplish their functions by binding to a family of receptor tyrosine kinases that span the cell membrane of the endothelial cells. This signal causes the differentiation of mesodermal cells into endothelial cells as well as their proliferation. When the Flk1 genes are knocked out, the mice die at embryonic day 8, and they lack endothelial cells. In the absence of this signal, blood vessels fail to form from the endothelial cells, and the mouse dies at embryonic day 8.