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And what I want to show you now is, that these very very simply is the systemic circulation.
我要介绍的就是系统循环（体循环）的内容
Systemic circulation.
体循环
Now, of course you know that there is also the pulmonary circulation.
当然大家知道除了体循环，还有肺循环
So what does that look like?
肺循环又是怎样呢？
Let me draw that here --pulmonary circulation.
我们来画一下肺循环
So pulmonary, you know, means lungs.
pulmonary意思就是“肺部的”
And I've shown you previously, in another video, that there is blood going to these lungs.
之前我们介绍过血液在低压的情况下
In a very low pressure system.
流入肺部
So we talked previously about low pressure and high pressure systems.
之前我们介绍过高低压的问题
And now just remember that this is kind of how it gets there,
现在复习一下血液的流动
you have the deoxygenated blood, or the -- the blood in the blue vessel, kind of going up like that,
这是缺氧血，蓝色血管中的血液这样流动
and this should be the pulmonary artery. Pulmonary artery.
这是肺动脉
I'll write Art. for artery. And we have the pulmonary vein, bringing that blood back to the heart with oxygen in it.
Art代表“动脉Artery”，将含氧血运回心脏
Pulmonary vein.
这是肺静脉
So that's your pulmonary circulation,
这就是肺循环
so your pulmonary circulation and your systemic circulation.
这分别就是肺循环和体循环
And I'll get back to why I drew the pulmonary artery in blue,
之后我会解释为什么肺动脉用蓝色画
and pulmonary vein in red, in just one second.
而肺静脉用红色
Let's put that on the side for a momment.
好，我们把这点先放到一边
And let's get into exactly how to think about arteries and veins in general.
下面我们来看什么是动脉，什么是静脉
So in general, I think of arteries as taking blood away from the heart.
总的来说，动脉就是将血液运离心脏
That's probably the easiest and most clear way of figuring out what an artery is exactly.
这么想应该是对动脉最简单的定义方式
So, arteries are taking blood AWAY from the heart.
动脉就是输送血液离开心脏的血管
So let me just draw a little arrow here.
我画一下箭头标明方向
And veins are bringing blood back.
静脉则是将血液送回心脏
And so this becomes our first point.
这是第一个不同点
Point number one, and this is the point of difference between the two of them,
大家看，这是动脉和静脉的第一个不同点
is the direction of flowing,
就是血液流动方向
and even if you see at pulmonary system, you can see that --that remains true,
即便是肺循环的系统，大家可以看到，这也是成立的
that the arteries are taking blood away, and the vein is bringing the blood back.
动脉输送血液离开心脏，动脉则将血液送回心脏
Okay. Point number two.
好，看第二个不同点
Now you see that the arteries are drawn in red, for the most part.
好，大家看到，一般来说动脉是用红色画的
And so usually arteries have oxygenated blood, that they're bringing out to the tissues.
一般来说，动脉是向组织输送含氧血
And then the veins carry the deoxygenated blood, that they bring back from the tissue.
而静脉呢，则是从组织中将缺氧血运送回来
So point number two, is really about the colour.
所以第二个不同点，就是血液颜色
And so let me write that in here.
我们写一下
So this would be like a little red blood cell with hemoglobin in it.
那么这里就是有血红蛋白的红血球
And this is a little red blood cells -- still called the red blood cell
这是红血球，也叫红细胞
even though its colour is more blue,
虽然颜色偏蓝色
but it's still got the hemoglobin in it,
但含有血红蛋白
but the hemoglobin down here --down here, actually doesn't have any oxygen left,
在这里，其实细胞中已经不剩多少氧气了
and so the colour looks quite different.
所以颜色就不一样了
So the colour of arterial blood is usually red,
动脉血一般是红色的
because of the fact that oxygen is bound to the hemoglobin.
因为氧气跟血红蛋白结合在一起
And less oxygen is bound on the venous side,
而静脉中与血红蛋白结合的氧气相对较少
so that's why it turns blue.
所以静脉用蓝色画
Now, I want to --just put little star there, because that's not always true.
这里我们用一个星号标一下以表示这并不总是成立的
And you can see where clearly it's not true, it's over here.
大家也可以看到，看这里
