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Where I left off in the last video,
上集视频中
we talked about how the hemoglobin in red blood cells is what sops up all of the oxygen
我们介绍了红细胞中的血红蛋白是吸收氧气的地方
so that it increases the diffusion gradient
所以血红蛋白会增加血液中的扩散梯度
or it increases the incentive, we could say, for the oxygen to go across the membrane.
或者说，促进氧气透过细胞膜扩散
We know that the oxygen molecules don't know that there's less oxygen here,
氧气分子本身并无法判断什么地方氧气浓度更低
but if you watch the video on diffusion you know how that process happens.
但如果看扩散的视频的话，大家会看到这个过程
If there's less concentration here than there,
如果某地方浓度要小于别的地方
the oxygen will diffuse across the membrane
氧气就会透过细胞膜进行渗透
and there's less inside the plasma because the hemoglobin is sucking it all up like a sponge.
所以血浆中氧气浓度很低，因为血红蛋白像海绵吸水一样把氧气都吸收了
Now, one interesting question is,
这里有一个很有意思的问题
why does the hemoglobin even have to reside within the red blood cells
为什么血红蛋白要在红细胞中呢？
Why aren't hemoglobin proteins just freely floating in the blood plasma?
为什么不直接让血红蛋白在血浆中流动呢？
That seems more efficient.
这样看起来扩散更有效率
You don't have to have things crossing through, in and out of, these red blood cell membranes.
因为这样的话，氧气不用再透过细胞膜进行扩散了
You wouldn't have to make red blood cells.
这样也不用专门生成红细胞了
What's the use of having these containers of hemoglobin?
那么为什么还要把血红蛋白放在红细胞里呢？
It's actually a very interesting idea.
这个很有意思
If you had all of the hemoglobin sitting in your blood plasma, it would actually hurt the flow of the blood.
如果把血红蛋白直接放在血浆里，这样会妨碍血液流动
The blood would become more viscous or more thick.
血液会变得更加粘稠
I don't want to say like syrup, but it would become thicker than blood is right now
说很像糖浆可能不太恰当，但血液确实会比现在更粘稠
and by packaging the hemoglobin inside these containers, inside the red blood cells,
而如果把血红蛋白包裹在细胞中，由红细胞来运送
what it allows the blood to do is flow a lot better.
这样血液流动更流畅
Imagine if you wanted to put syrup in water.
假设大家把糖浆倒在水里
If you just put syrup straight into water, what's going to happen?
直接倒在水里的话，会怎样呢？
The water's going to become a little syrupy, a little bit more viscous and not flow as well.
水会变得粘稠起来，流动就不顺畅了
So what's the solution if you wanted to transport syrup in water?
那么，怎么解决这个问题呢？
Well, you could put the syrup inside little containers or inside little beads
我们可以用小容器把糖浆先装起来，比方说小珠子内部装糖浆
and then let the beads flow in the water
然后让小珠子在水里流动
and then the water wouldn't be all gooey and that's exactly what's happening inside of our blood.
这样水就不会变得黏稠，这也是血液中的情况
Instead of having the hemoglobin sit in the plasma and make it gooey,
血红蛋白直接在血浆中，血液就会非常黏稠
it sits inside these beads that we call red blood cells that allows the flow to still be non-viscous.
但如果放在红细胞中血液就不那么黏稠
So I've been all zoomed in here on the alveolus and these capillaries,
我们看放大图里的肺泡和毛细血管
these pulmonary capillaries-- let's zoom out a little bit-- or zoom out a lot-- just to understand, how is the blood flowing?
这些肺部毛细血管--我们从宏观上看一下，看血液是怎么流动的
And get a better understanding of pulmonary arteries and veins relative to the other arteries and veins that are in the body.
要看肺部的动脉和静脉区别于身体中的其他静脉和动脉的工作原理
