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心脏位于胸腔的正中央，从胚胎的第四周开始为人体输送血液，直到死亡为止，从不停止，这个过程大约为人体循环输送1.75亿升血液。本系列课程介绍了人体整个循环系统的组成与各部分的功能，主要内容包括：心脏，血管，血压，淋巴，胎儿与成人的循环过程，血压控制，心肌收缩，心脏的神经调节等内容。
adj. 次等的，较低的，不如的
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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
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