If it expanded its radius,

如果血管的半径扩大
the rate of low would go up even though the pressure drop remains the same.

在压差保持不变时流速就会增加
Does that make sense?

听明白了么
I mentioned before that arteries, arterioles, small arteries,

我之前讲过像动脉细动脉小动脉
all arteries have muscular walls.

所有的动脉都有肌肉壁
They have a special kind of muscle called smooth muscle

这种特殊的肌肉叫做平滑肌
which is arranged circumferentially,

沿着圆周方向
sort of wrapped around the vessel,

包裹在血管外侧
and that muscle can contract to constrict the vessel

这些肌肉收缩就能压缩血管
or relax to dilate the vessel.

放松的话血管就扩张
One feature of arteries that makes them important in physiology

在生理学上动脉的一个特征十分重要
is that they can change their diameter.

就是它能改变自身的直径