Blood Vessel Diseases
Arteries vs. Veins - What's the difference? Learn some important differences between arteries (high pressure/low volume) and veins (low pressure/high volume). Rishi is a pediatric infectious disease physician and works at Khan Academy.
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- Okay let's talk about the arteries and the veins
- and I'm actually going to talk about the both of them
- and simultaneously because there are some interesting
- differences I want to point out between the two. You know that they're both vessels but
- there are some really important differences between how they work and what they do.
- So this is your heart and coming out of your heart is the aorta
- and before this video I have been drawing the aorta quite differently,
- kind of showing its branches and here I am showing it kind of stretched out.
- and I'll show a few of the branches but really the point of the drawing is not to make it anatomically correct,
- you can tell that definitely it's not anatomically correct,
- because that wouldn't make any sense at all,
- that blood going off to one side.
- But really, I want to show you a concept in this video.
- A few concepts, actually. So, here we have --let's say, the vein.
- And I'm gonna stretch that out as well, and let's imagine that
- all of the veins are dumping into this one final vein.
- It gets back to the --to the heart.
- So I'll draw the branches kind of coming in to the vein here and here.
- And we know that the arteries and the vein are trying to get blood out to the capillaries.
- So these show you what a zoomed in version may look like of the capillaries.
- So we've got --let's say, some capillaries, here and maybe some here and here.
- And you know of course in real life you don't have three such a capillary beds,
- which is what I'm drawing here, but really of thousands and thousands, right?
- And let's not to forget, you know,
- these capillaries are basically found in different parts in the body,
- so you might have --for example, a bone, and some capillaries in the bone,
- you may have this second capillary, may be, going to your face,
- let's say even specifically, your nose.
- And this third capillary bed, may be going down to your foot.
- So you have blood in your foot.
- So you have different parts of the body all getting capillaries and
- the blood is gonna start at the heart, go to the capillaries through the arteries,
- and then return through all those beds.
- And we've kind of lumped it together.
- And what I want to show you now is, that these very very simply is the systemic circulation.
- Systemic circulation.
- Now, of course you know that there is also the pulmonary circulation.
- So what is that look like?
- I mean to draw that here --pulmonary circulation.
- So pulmonary, you know, means lungs.
- And I've shown you previously, in another video, that there is blood going to these lungs.
- In a very low pressure system. So we talked previously about low pressure and high pressure system.
- And now I just remember that this is kind of how it gets there,
- you have deoxigenated blood, or the --the blood in the blue vessel,
- kind of going up like that, and this should be the pulmonary artery.
- Pulmonary artery.
- All right, {Art.} for artery. And we have the pulmonary vein,
- bringing that blood back to the heart with oxygen in it.
- Pulmonary vein.
- So that's your pulmonary circulation, so your pulmonary circulation in your systemic circulation.
- And I'll get back to why I drew the pulmonary artery in blue,
- and pulmonary vein in red, in just one second.
- Let's put that on the side for a momment.
- And let's get into exactly how to think about arteries and veins in general.
- So in general, I think of arteries as taking blood {AWAY} from the heart.
- That's the easiest and most clear way of figuring out what an artery is exactly.
- So, arteries are taking blood AWAY from the heart.
- So let me just draw a little arrow here.
- And veins are bringing blood {BACK}. And so this becomes our first point.
- Point number one, and this's the point of difference between the two of them,
- is the direction of flowing, and even if you see at pulmonary system,
- you can see that --that remains true, that the arteries are taking blood away,
- and the vein is bringin the blood back.
- Okay. Point number two. Now you see that the arteries are drawn in red, for the most part.
- And so usually arteries have oxygenated blood, that they're bringing out to the tissues.
- And then the veins carry the deoxygenated blood, that they bring back from the tissue.
- So point number two, is really about the colour.
- And so we write that in here.
- So this should be like a little red blood cell with hemoglobin in it.
- And this is a little red blood cells --
- still called the red blood cell eventhough its colour is more blue,
- but it still got the hemoglobin in it,
- but the hemoglobin down here --down here, actually doesn't have any oxygen left,
- and so the colour looks quite different.
- So the colour of arterial blood is usually red, because of the fact that oxygen is bound to the hemoglobin.
- And less oxygen bound in the venous side, so that's why it turns blue.
- Now, I want to --just a little star there, because that's not always true.
- And you can see where clearly it's not true, it's over here.
- So I'd like to --let me star the pulmonary circulation,
- where you can see that the pulmonary artery and vein --I'll star that,
- that's just really emphasize the point, or actually the reverse of what I've just said, right.
- Because the pulmonary artery is actually gonna carry deoxygenated blood,
- and the pulmonary vein is carrying oxygenated blood.
- So clearly that's the reverse of what I've just side.
- But that is one exception to the general rule,
- which is that arteries definitely look red, and veins generally look blue.
- Okay, so that --those are two points of difference between the arteries and veins.
- Let's keep going. So now you know, that arteries are high pressure, right.
- because the heart is pumping the blood out, and it's gonna be in a very very high pressure.
- And so I kind of think the arteries as being like a river, a fast flowing river.
- So you can think of this as fast flowing, high pressure.
- So that is the third difference. This is a high pressure system.
- Third difference, it's that it's high pressure system.
- In fact, maybe I'll even emphasize the point by writing the word very large:
- HIGH PRESSURE.
- And actually, the other thing we think about with these arteries is that there is not so much volume in the arteries.
- So if you actually look at --let's say, first time now,
- you should try figure out where all the blood was located,
- not too much of it is in the arteries.
- So it's very low volume system, right, its volume is very small.
- And the veins are the opposite. They're kind of a large volume-- system.
- And they have really kind of a low pressure.
- Alright, pressure is very small over here.
- And if you actually figure out what percent is where,
- in terms of the amount of blood, about 5% of the blood, at any point time,
- would be in the heart. And --let's say, about 5% would be in the capillaries.
- and then about 10% or so, would be in the lungs.
- So what we have to --now we're 5 and 5 is 10, 10 plus 10 is 20.
- And then we have another about 15% in the arteries. So about 15%.
- So that's actually not too much blood.
- And so the remaining --what is that, 65% of the blood, is actually in the vein, in any point of time.
- So that's remarkable, right. About two third of the blood in any point time is actually sitting in all the vein combined.
- And so the way I've drawn it, isn't really --not really a best way to draw it.
- I should really erase this. And really redraw this to make it much more accurate.
- It should look a lot more like this, right, like a big giant lake of blood.
- And so this is actually how to think about of the vein.
- It's actually very very low pressure but high volume system.
- So that may be the third point. I'll bring up on the blood side --or, on the vein side.
- it's that it's a high volume system. so, high volume.
- Now, we've talked about the direction of flow,
- we've talked about the fact that one side carries more oxygen than the other,
- and we've also talked about the fact that arteries are high pressure-low volume system.
- And the veins are high volume-low pressure system.
- So what are some other differences?
- So, one other difference is that in the arteries, you actually don't have any valves.
- Now --I don't know how to label that to make it super clear, but let me just find some sort open spot here,
- and write number four, there're no valves in the arterial system,
- whereas on the venous side, you actually do have valves.
- You have these valves come together --we make it very clear, but making the two sides touch.
- And the blood kind of goes through like that.
- So you have these valves keep the blood going in the right direction.
- So that would be the fourth point of difference between the two.
- So you have these valves. And you might get confused, because you think,
- "well, doesn't the heart also have valves?"
- And it does, the heart also has valves.
- But the veins have a different type of valves, and that's actually keep the blood flowing in the right direction.
- You can imagine that you probably don't even need that on the arterial side,
- because the pressures are so high, that the blood is forced to go one way.
- Or, it's in the vein, because it's kind of a giant lake.
- Water can kind of swirl around and around and around,
- and so it's helpful to have valves keeping going in the right direction.
- So that's the fourth point of difference.
- So now think about of the fact that you might have, a break in the arterial system.
- So let's say that you have an accident, and you cut an artery --or, a big artery, let's say.
- What would it look like? So if you have a break right here,
- you would actually have like a fountain of blood, coming out, right there.
- Because it's under such high pressure, it's gonna spew up, right.
- And so this is basically what it looks like when you actually cut your artery,
- again, because of the fact that it's under such high pressure.
- And on the venous side, on the vein side, if you have a break. It looks really different.
- Because you have --let's say your break is right here,
- you'd actually get a kind of --a pool of blood, just locally, before it clots off.
- Because again, you have a very low pressure. So it's just gonna kind of quietly pool and,
- you might get a bruise right there.
- But it's really won't look like a fountain of blood.
- And that's actually another final point of difference which,
- really gets back to the high pressure system on the arterial side,
- and the high volume-low pressure system on the venous side.
- ~o0o~
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At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
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