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It's an amazing pump, pushing blood, so that you have good blood flow.
心脏就是一个泵，不断把血液抽入，推出，维持血液流动
And so I'm going to write that on the side as kind of job number one.
这是心脏的第一个工作
These are the jobs of the heart.
这边我们写一下心脏的工作有什么
So jobs, and number one, would be blood flow.
第一，维持血液流动
And I'll write systemic flow. Systemic flow.
这属于体循环
And all that systemic means is that I'm refering to the entire body.
体循环就是相对于全身来说的
So systemic when I say that word, I just mean the entire body.
这是针对于全身的
All the cells in the body.
全身的每个细胞
Now, exactly how that happens actually you can see on this picture.
看这个图，大家会明白原理
So, here you have a giant vein, this is a vein, and you have an artery here.
这里有一条大静脉，这里有一条动脉
This is an artery.
这是动脉
And blood is actually going through the artery, that way.
血管从这个方向通过动脉
And it's actually coming into two veins, the one at the top,
进入两条静脉，一条在上边
this is called the superior, superior just kind of means at the top.
叫superior--其中superior意思就是上部
Superior vena cava. That's the name of the vein.
这条静脉叫上腔静脉
And at the bottom here, you can't see it because it's on the other side of the heart,
而下边，这里在心脏另一边，大家是看不到的
but there's another vein called the inferior vena cava.
这里还有一条静脉，是下腔静脉
And these two veins, this is also a vein,
这两条静脉
these two veins are actually dragging blood in from all over the body, into the heart.
从全身抽取血液回来，流入心脏
And then, when the heart is ready to pump it back out,
当心脏完成工作，要把血液送回全身时
it goes into this artery, and the name of it is the aorta.
就把血液送到这条动脉，名字是主动脉
So if you've heard of the aorta,
大家可能听说过主动脉
this is the artery that people are talking about.
说的就是这条动脉
So this is how blood comes and gets pumped around.
这是血液流出心脏的通路
But this isn't actually the only job of the heart.
当然，这不是心脏唯一的工作
The job, the second job of the heart, is actually also in this picture, and it's called pulmonary flow.
心脏还有第二个工作也在图中标出了，叫做肺循环
Pulmonary flow. So, what does that mean?
肺循环是什么意思呢？
Well, we know that cells are expecting oxygen, right?
我们知道细胞生存需要氧气
We know this. And that they have a lot of carbon dioxide waste.
同时产生很多二氧化碳废物
Well, it's good to move things around.
这些物质都需要搬运
It's good to move blood around.
血液需要流动
But if you actually never got rid of that carbon dioxide or brought in new oxygen,
但除非丢掉这些二氧化碳废物，或者说补充氧气
then a cell is not going to be very happy either.
细胞才能持续存活
I mean, you can have blood flow,
所以只有血液循环是不够的
but at some point it's also going to want some oxygen.
还要补充氧气
And it's going to want to get rid of that carbon dioxide.
同时要把二氧化碳代谢出去
So, that's where the lungs come in.
这时就要考虑到肺了
So what happens is that the heart, before sending blood out the aorta,
在心脏把血液送入主动脉之前
before just dishing it back out to the body,
送回身体各处之前
it actually sends the blood over to the lungs.
先把血液送入肺部
And it goes over to the left lung, and to the right lung.
进入左肺和右肺
And the blood comes back from the right lung and the left lung,
经过两个肺之后
and gets pushed back into the heart, and then gets squeezed through the aorta.
送回心脏，再送入主动脉
So there's this actual extra little step here,
在肺中的这个步骤
where blood is going to and from the lungs, and that's the pulmonary flow.
这个过程叫肺循环
