Define angiogenesis.

• A. Destruction of old vessels
• B. Formation of new blood vessels from preexisting vessels
• C. Clot formation
• D. Vasoconstriction

Answer: (B)

Angiogenesis is the formation of new blood vessels from preexisting vessels. It starts with signals such as VEGF that stimulate endothelial cells to proliferate and migrate, followed by sprouting of new capillaries, tube formation, and maturation with support from pericytes and extracellular matrix. This process expands blood supply during development, wound healing, and in response to low oxygen, and it also plays a role in tumor growth when tumors recruit their own blood vessels. In contrast, destroying old vessels describes vascular regression, clot formation is thrombosis, and vasoconstriction is the narrowing of vessels. So the description of forming new vessels from existing ones best defines angiogenesis.