Vasculogenesis

Vasculogenesis is the process of blood vessel formation occurring by a de novo production of endothelial cells.

Process
Though similar to angiogenesis, the two are different in one aspect: The term angiogenesis denotes the formation of new blood vessels from pre-existing ones, whereas vasculogenesis is the term used for the formation of new blood vessels when there are no pre-existing ones. For example, if a monolayer of endothelial cells begins sprouting to form capillaries, angiogenesis is occurring. Vasculogenesis, in contrast, is when endothelial precursor cells (angioblasts) migrate and differentiate in response to local cues (such as growth factors and extracellular matrix) to form new blood vessels. These vascular trees are then pruned and extended through angiogenesis.

Occurrences
Vasculogenesis occurs during embryologic development of the circulatory system.

Vasculogenesis can also occur in the adult organism from circulating endothelial progenitor cells (derivatives of stem cells) able to contribute, albeit to varying degrees, to neovascularization. Examples of where vasculogenesis can occur in adults are:
 * during tumor growth
 * revascularization process following trauma, e.g., after cardiac ischemia
 * Endometriosis - It appears that that up to 37% of the microvascular endothelium of the ectopic endometrial tissue originates from endothelial progenitor cells.