Vasculogenesis and angiogenesis

• Blood vessel formation in the extraembryonic splanchnic mesoderm of the yolk sac begins on day 17 and is directly coupled to hematopoiesis
• he hemangioblasts that surround the blood islands become endothelial precursor cells (EPCs) that differentiate into endothelial cells.
• vasculogenesis → Endothelial cells that organize themselfs in small capilary vessels. (vessel formation in yolk sac)
• Blood vessel formation in the intraembryonic splanchnic mesoderm begins as early as day 18 but is not coupled to hematopoiesis.
• Endodermal cells induce some cells of the splanchnic mesoderm to differentiate into EPCs, here also called angioblasts
• Through the fusion of vasculogenic cords, a network of blood vessels is formed throughout the embryonic disc.
• Angiogenesis → expanding and remodeling the vascular system using existing endothelial cells and vessels generated by vasculogenesis.
• Two mechanisms that are involved in angiogenesis:

  • sprouting: budding of new vessels from existing endothelial cords
  • vascular intussusception: splitting or fusion of existing blood vessels