Which term describes the dilation of blood vessels in active tissues?

• A. Vasoconstriction
• B. Vasodilation
• C. Angiogenesis
• D. Endothelization

Answer: (B)

Dilation of blood vessels in active tissues is vasodilation. When tissues are active, they release signals such as CO2, lactic acid, adenosine, and nitric oxide that cause the smooth muscle in arterioles to relax. This relaxation lowers resistance and increases blood flow to meet the higher metabolic demands, a response known as functional or active hyperemia. This is the opposite of vasoconstriction, which narrows vessels to reduce flow, and it’s not about growing new vessels (angiogenesis) or endothelial coverage (endothelization).