and they do that by looking at what's called a tracer molecule.

实现的方法是靠称为示踪分子的物质
In this case, insulin[inulin] is a tracer.

在本例中胰岛素[口误菊糖]即为示踪分子
It's picked for its particular properties,

选中它是因为它的特殊性质
that it's filtered freely in the glomerulus

它能被肾小球自由率过
but neither reabsorbed nor secreted.

但既不重吸收也不排泌
It allows you to calculate some physiological function

从而使你能够计算某些身体内部深处的
sort of deep inside your body, so you can

生理功能因此你能
measure glomerular filtration rate this way.

用这种方式测量肾小球滤过率
I've already showed you this picture that shows

我已经给你们看过这张肾血管系统的图了
the vascular system of the kidney, sort of laid out in a line here.

基本上在这条线上展开
Here's the renal artery branching into afferent arterioles,

这里肾动脉分叉成为入球小动脉
branching into glomerular capillaries,

分叉成为肾小球毛细血管