Similar to highways, roads, paths and trails reaching the different communities of a country, vessels get to all parts of an organism and they are spatially organized for trafficking capacity to achieve efficient circulation of blood. In vertebrates, this network is so important that no solid tissue survives above 1–2 mm in diameter without being vascularized and connected to the functioning cardiovascular system. This applies to embryonic development as well. Therefore, it is not surprising that in embryos of many species the cardiovascular system is the first functional system to be developed. In the mouse just four days after implantation, the embryo has to have a functional heart with connected vessel structure to the embryo, yolk sac, and placenta in order to survive. The vasculature is developing from early embryonic stages until the end of juvenile phase, as long as an individual is growing (Gerber et al. 1999). After this growth phase, vessel formation ceases except in organs subject to periodical remodeling, such as ovary and uterus, and in physiological/pathological conditions, such as wound healing and tumor growth.