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And what I want to show you now is, that these very very simply is the systemic circulation.
我要介紹的就是系統循環（體循環）的內容
Systemic circulation.
體循環
Now, of course you know that there is also the pulmonary circulation.
當然大家知道除了體循環，還有肺循環
So what does that look like?
肺循環又是怎樣呢？
Let me draw that here --pulmonary circulation.
我們來畫一下肺循環
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.
之前我們介紹過血液在低壓的情況下
In a very low pressure system.
流入肺部
So we talked previously about low pressure and high pressure systems.
之前我們介紹過高低壓的問題
And now just remember that this is kind of how it gets there,
現在復習一下血液的流動
you have the deoxygenated blood, or the -- the blood in the blue vessel, kind of going up like that,
這是缺氧血，藍色血管中的血液這樣流動
and this should be the pulmonary artery. Pulmonary artery.
這是肺動脈
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“動脈Artery”，將含氧血運回心臟
Pulmonary vein.
這是肺靜脈
So that's your pulmonary circulation,
這就是肺循環
so your pulmonary circulation and your systemic circulation.
這分別就是肺循環和體循環
And I'll get back to why I drew the pulmonary artery in blue,
之后我會解釋為什么肺動脈用藍色畫
and pulmonary vein in red, in just one second.
而肺靜脈用紅色
Let's put that on the side for a momment.
好，我們把這點先放到一邊
And let's get into exactly how to think about arteries and veins in general.
下面我們來看什么是動脈，什么是靜脈
So in general, I think of arteries as taking blood away from the heart.
總的來說，動脈就是將血液運離心臟
That's probably the easiest and most clear way of figuring out what an artery is exactly.
這么想應該是對動脈最簡單的定義方式
So, arteries are taking blood AWAY from the heart.
動脈就是輸送血液離開心臟的血管
So let me just draw a little arrow here.
我畫一下箭頭標明方向
And veins are bringing blood back.
靜脈則是將血液送回心臟
And so this becomes our first point.
這是第一個不同點
Point number one, and this is the point of difference between the two of them,
大家看，這是動脈和靜脈的第一個不同點
is the direction of flowing,
就是血液流動方向
and even if you see at pulmonary system, you can see that --that remains true,
即便是肺循環的系統，大家可以看到，這也是成立的
that the arteries are taking blood away, and the vein is bringing the blood back.
動脈輸送血液離開心臟，動脈則將血液送回心臟
Okay. Point number two.
好，看第二個不同點
Now you see that the arteries are drawn in red, for the most part.
好，大家看到，一般來說動脈是用紅色畫的
And so usually arteries have oxygenated blood, that they're bringing out to the tissues.
一般來說，動脈是向組織輸送含氧血
And then the veins carry the deoxygenated blood, that they bring back from the tissue.
而靜脈呢，則是從組織中將缺氧血運送回來
So point number two, is really about the colour.
所以第二個不同點，就是血液顏色
And so let me write that in here.
我們寫一下
So this would be like a little red blood cell with hemoglobin in it.
那么這里就是有血紅蛋白的紅血球
And this is a little red blood cells -- still called the red blood cell
這是紅血球，也叫紅細胞
even though its colour is more blue,
雖然顏色偏藍色
but it's still got the hemoglobin in it,
但含有血紅蛋白
but the hemoglobin down here --down here, actually doesn't have any oxygen left,
在這里，其實細胞中已經不剩多少氧氣了
and so the colour looks quite different.
所以顏色就不一樣了
So the colour of arterial blood is usually red,
動脈血一般是紅色的
because of the fact that oxygen is bound to the hemoglobin.
因為氧氣跟血紅蛋白結合在一起
And less oxygen is bound on the venous side,
而靜脈中與血紅蛋白結合的氧氣相對較少
so that's why it turns blue.
所以靜脈用藍色畫
Now, I want to --just put little star there, because that's not always true.
這里我們用一個星號標一下以表示這并不總是成立的
And you can see where clearly it's not true, it's over here.
大家也可以看到，看這里
