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So you've seen one key difference now with these large and middle sized arteries.
刚介绍了静脉和大中型动脉的主要不同之处
Okay so now let's go to the small arteries and the arterioles.
下面看小动脉和微动脉
So here let's start out with the lumen, has that as before.
还是从内腔开始
And you also have a large tunica media.
这里中膜也是很厚的
So unlike the vein, the tunica media in the arteries
有别于静脉，两类动脉中的中膜
in both types of arteries- is actually quite large.
都非常厚的
Except here, instead of having elastin in this area,
不过大中型动脉中是弹性蛋白
you have just tons and tons of muscle. Lots of muscle.
而这里就是非常多肌肉细胞而已
So they're very very strong in the sense that
这样血管会强劲有力
you can actually very easily squeeze down on the lumen
肌肉收缩的话
if you wanted to by having all of this muscle contract.
血液的输送会非常简单
And that makes sense because we know that the arterioles - look at all of that muscle-
我们知道，大家看小动脉中的这些肌肉细胞
the arterioles are actually going to be the ones that are going to create resistance.
我们知道小动脉的功能是增加血流阻力
So here you have a lot of muscle.
这里肌肉细胞很多
And this is to help create lots of resistance.
这样可以产生很大的血流阻力
If you need it, to change your blood pressures.
如果情况需要，可以改变血管血压
So that's why the small arteries and arterioles are really helpful in squeezing down and changing blood pressures
所以我们说，在送血和调节血压方面，小动脉和微动脉非常重要
And on the outside, they as before, have that layer of tunica externa.
外层的话，就是一般的外层
And this again is where the nerve endings go,
神经末梢也在这一层
and where the blood vessels, or the vasa vasorum go.
血管滋养层也是在这一层
So that's where that layer is.
就是这一层
Okay. And you might be thinking
好，大家可能想到
there's gotta be one more vessel type and there is- and that's the capillary.
还有一种血管类型就是毛细血管
So let me draw the capillary, so I'll do that over here.
我在这里画一下毛细血管
The capillary is actually going to look different from all of this other stuff that we've done
毛细血管跟我们刚画的这些看起来不太相同
because the capillaries are actually really really unique in the sense that-unlike we had for the veins and arteries
毛细血管相对于动脉和静脉来说是比较独特的
this is down to the single cell level. Right?
这是在细胞层面上来讲的
So you still have a lumen but on the outside,
里边还是内腔
instead of having a lot of endothelial cells you actually have, at times, one cell.
但外边不是内皮细胞，而是一个细胞
One cell will actually form the entire wall of the tube.
一个细胞就构成了血管壁
So you actually have a cell travelling within a cell.
毛细血管实际上是红细胞在一个细胞中流动
Almost like the cell is giving- the little red blood cell is floating through a big hug or something like that.
可以说红细胞是在一个血管细胞的环抱中流动的，大家可以想象一下
So that capillary looks actually quite different
所以毛细血管的形态是非常不同的
as you can see from the other things that we've drawn: the veins and arteries.
大家可以看一下别的图示，静脉和动脉的图示
But I want you to just take a look at this again
大家再看一下
and see the key differences between the veins and arteries.
比较一下静脉和动脉之间的差异
The vein follows the general pattern.
静脉血管跟一般血管的构成吻合
But the large and middle arteries have a lot of elastin in the tunica media.
大中型动脉在中层有很多弹性蛋白
And the small arteries and arterioles have a lot of muscle in that tunica media.
小动脉和微动脉则是在中膜有很多肌肉细胞
