when a liquid meets a solid is so high

所遇到的摩擦十分大以至于
that fluid at the surface doesn't really move at all.

与表面直接接触的液体其实并不流动
For low rates, fluid that's right at the surface doesn't move at all,

对低速流体表面流层实际上并不移动
and so roughness doesn't matter when you have no flow there.

因此管壁本身的粗糙度不会产生影响
As the flow rate increases then roughness becomes more important.

随着流速增加粗糙度才变得重要
Two things about it in our vascular systems,

我们的血管系统有两个特点
the flow rates are generally low enough

一来血液流速通常较低
that you don't have worry about that.

这一点你无须担心
Our vessels are all really very similar

还有就是从微观几何学的角度而言
in terms of their microscopic geometry,

人类所有的血管都十分相似
and that all of the blood vessels are covered

所有血管表面都覆盖着一层单层细胞
with a monolayer of cells called endothelial cells

称为上皮细胞