The doctor explained that the medication works by enhancing blood circulation throughout the body.

circulation 是名词，来自动词 circulate（循环、流通），由词根 circ-（圆、环）和后缀 -ulate（使...）组成，字面意思是"使形成循环"。在医学语境中特指"血液在体内的循环流动"。