Angiogenesis is the process of the formation of new blood vessels from pre-existing vascular structures, which is needed for oxygenation of - and providing nutrients to - expanding tissue. Angiogenesis takes place through different modes of action. Coalescent angiogenesis is a mode of angiogenesis where vessels coalesce or fuse to increase blood circulation. This process transforms an inefficient net structure into a more efficient treelike structure. It is the opposite of intussusceptive angiogenesis, which is where vessels split to form new vessels.