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This is now going to dump into what we call a venule. A venule.
这时血液进入小静脉。小静脉
And this venule is gonna basically then feed into many, many other venules.
大家看这条小静脉会跟无数其他小静脉汇合
Maybe there's a venule down here coming in, and maybe a venule up here coming in.
可能这里有一条小静脉进来，这里有一条小静脉进来
Maybe from the second toe,
可能这条小静脉来自第二个脚趾
and it's gonna basically all kind of gather together,
所有小静脉汇合
and again, to a giant, giant set of veins.
得到一个大的静脉束
You know, maybe veins are dumping in here now, maybe another vein dumping in here,
可能这里有静脉汇入，可能这里还有别的静脉
and these veins are all going to dump into an enormous vein that we call the inferior vena cava.
这些静脉都汇入一条大静脉，叫做下腔静脉
I'll write that right here. Inferior vena cava
我写在这，这就是“下腔静脉”
And this is the large vein that brings back all the blood from the bottom half of the body.
这是把所有血液从身体下部各处送回心脏的大静脉
There's also another one over here called the superior vena cava,
当然还有一条上腔静脉
and this is bringing back blood from the arms and head.
上腔静脉是输送胳膊、头部血液的大静脉
So these two veins, the superior vena cava and the inferior vena cava, are dragging the blood back to the heart,
上腔静脉和下腔静脉这两条静脉将血液送回心脏
and, generally speaking, these are all considered, of course, veins.
这些都是静脉血管
Let's back up now and start with the large and medium arteries.
下面我们看大中型动脉
These guys together are sometimes referred to as elastic arteries.
上边这两组，叫做弹性动脉
Elastic arteries, and the reason they're called elastic arteries,
弹性动脉是什么意思呢？为什么它们叫弹性动脉呢？
one of the, one of the good reasons why they're called that is that
之所以它们叫弹性动脉
they have a protein in the walls of the blood vessel called elastin.
是因为这些血管壁中存在一种弹性蛋白
They have a lot of this elastin protein, and, if you think about the word elastin or elastic,
存在大量的弹性蛋白。大家看着两个词 “弹性蛋白”和“弹性”
you know, obviously similar words, you might think of something like a rubber band or a balloon,
很相近，大家想一下橡皮筋或者气球
and that's probably the easiest way to think about it.
这样比较好理解
If you have a blood vessel, one of these large arteries for example,
那么假设有一条大动脉
and let's say blood is under a lot of pressure, right?
血压是很高的
Because the heart is squeezing out a lot of high pressure blood
心脏把血液挤压输送出去，那么动脉血压是很高的
This artery is literally going to balloon out,
那么血管可能就要膨胀
and if you actually looked at it from the outside, it would look like a little sausage.
从外边看的话，可能就像一根香肠
Something like this, where it's puffed out.
血管会有膨胀
So what's happened there between the first and second picture is that the pressure energy,
那么，在这两幅图之间发生变化的就是压力能
so the heart is squeezing out a lot of pressurized blood,
心脏把高压血液输送出去
and of course, there's energy in that blood, right?
能量就储存在血液中
That pressure energy has been converted over into elastic energy.
这部分压力能，就转化成了弹性能
It's actually converting energy.
发生了能量转换
We don't really always think about it that way, but that's exactly what's happening,
一般我们不这么来看，但确实是发生了能量转换
and when you convert from pressure energy to elastic energy,
压力能转换为弹性能的时候
what you are really then doing is you're balancing out those high pressures.
实际发生了什么呢？实际是平衡掉了血液的高压
So you're balancing out high pressures.
把血液的高压平衡一下
High pressures, and this is actually very important
为什么这么做呢？
because the blood that's coming into our arteries is under, let's not forget, high pressure.
因为动脉中的血液血压太高了，必须采取措施平衡一下
So the arteriole system, we know, is a high pressure system.
动脉系统是血压很高的系统
So this makes perfect sense that the first few arteries,
所以这些动脉
those large arteries and even those medium-sized arteries are going to be able to deal with the pressure really well
大动脉，甚至是中型的动脉必须要能承受血液的高压
