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  • So what you're looking at is basically

  • kind of a mechanistic way of thinking about the heart,

  • almost as if it's a couple of pumps

  • with pipes attached to the pumps.

  • And in a way, that's not a bad way to think about the heart.

  • In fact, we're going to kind of move through this diagram.

  • And I realize it looks a little bit scary.

  • But once I start labeling stuff, you'll

  • start seeing that it's actually not as bad as it seems.

  • So let's get started in the upper part of the heart.

  • The right atrium is right there, and then blood

  • goes down into the right ventricle.

  • And then on the other side, I'm going

  • to label the last two chambers, the left atrium

  • and the left ventricle.

  • And we're going to actually follow the path of blood

  • after it leaves the right ventricle.

  • We're going to start our journey here at the right ventricle.

  • So what's the first thing that kind of comes across?

  • Well, blood leaves the right ventricle,

  • goes through a valve.

  • And after, on the other side, you've

  • got this area right here.

  • And I've drawn it as one tube with no split,

  • and this is the pulmonary trunk.

  • So blood is headed towards the lungs,

  • going first through the trunk.

  • And of course, after the trunk there's a left and right.

  • So I'll write that up here.

  • The pulmonary arteries are next.

  • And remember, I call them arteries

  • because they're going away from the heart.

  • And there are two arteries.

  • So pulmonary arteries, left and right pulmonary arteries.

  • And that's why you see two things here.

  • One here, and you see one here.

  • And those are basically tubes.

  • So it's going from the pulmonary trunk.

  • It's splitting into one of the two tubes.

  • And now I'm drawing the left and right lung up top.

  • And of course, you know that the lungs are actually

  • not going to look this way.

  • So this is not anatomically correct.

  • But this is not, as I said in the beginning,

  • a bad way of thinking about it.

  • So blood goes through the lungs and then

  • comes out on the other side.

  • And there we're going to talk about

  • left and right pulmonary veins.

  • And actually, here I'm going to make the point that there

  • aren't just two pulmonary veins, one for each lung.

  • Actually, there are usually more than that.

  • And so when I draw this, too, I really

  • want you to just think of the two sides, veins

  • coming from both sides.

  • But the actual number could be a few pulmonary veins in total.

  • The pulmonary veins drain blood, then, into the left atrium,

  • right?

  • So now we're on the other side of the heart.

  • And for the moment, I'm going to kind of pause the journey here.

  • So we've gone from the right ventricle, around to the lungs,

  • back again in the left atrium.

  • And this is kind of the first part of our journey.

  • And this part of the journey is called

  • the pulmonary circulation.

  • I'm actually just going to write that here.

  • Pulmonary circulation.

  • So the fact that this part is going-- starting from the heart

  • and going back to the heart is one circuit,

  • and our heart actually has two circuits.

  • But I want to point out the circuits one at a time,

  • and we've already kind of completed one circuit.

  • So I'm going to take some blue paint

  • to indicate deoxygenated blood, or blood without oxygen.

  • I'm going to paint in how it would look.

  • And actually, it stopped there because my arrows.

  • But you can actually see now the deoxygenated blood kind of goes

  • from the right ventricle, through the pulmonary trunk,

  • through the arteries, and into the left and right lung.

  • And once it's there, it's going to kind of mix

  • in with the capillaries.

  • And it's going to start getting oxygen,

  • and then it's going to come out on the other side

  • in the pulmonary veins.

  • And it's again stopped a little bit there,

  • but I can fill it in.

  • And the pulmonary veins are going

  • to deliver that oxygenated blood to the left atrium.

  • So what you see kind of colored in now

  • is the pulmonary circulation.

  • That's the first part of our circuit.

  • But let's now keep going and now talk

  • about the second part of the circulatory system, which

  • is the systemic circulation.

  • So now the journey starts with the left ventricle,

  • so let me start there.

  • So for the systemic circulation, I'm

  • going to start the left ventricle.

  • And it's going to go around to the body, right?

  • The body is kind of the thing that's

  • going to be receiving all of the blood.

  • And when I say body, I really mean lots of things.

  • I mean things like the brain, so it

  • could be an organ like the brain or the liver.

  • It could also be maybe things like bones,

  • if you have bones in your fingers.

  • Could be the toes.

  • Could be any part of your body that you can think of, right?

  • So all these different organs and tissues

  • are going to be getting blood from the left ventricle.

  • It's going to be going initially through a giant vessel.

  • This vessel I'm going to label it say, here, as the aorta.

  • So this large vessel is the aorta.

  • And of course, it branches and splits.

  • And I haven't shown all the branches

  • that come off the aorta.

  • But there are many, many of them.

  • It goes to the various tissues and organs,

  • and then it comes back out on the other side.

  • And at the end, kind of somewhere up here,

  • it's going to go back to the right atrium.

  • And it generally travels through two major kind of vessels.

  • One is the inferior, and the other

  • is the superior, meaning lower and upper.

  • And they're both called vena cava.

  • So superior vena cava and inferior vena cava.

  • I'll just write that here.

  • So these are the two major veins that are bringing back blood

  • from all the different parts of the body.

  • And so now you've actually seen the second circulation,

  • because it all ends at the right atrium.

  • And this is the systemic circulation.

  • I'm going to write systemic circulation here.

  • So now you can see that the heart is really

  • two different systems-- or let's say two different circuits,

  • rather.

  • And the first one, the pulmonary circulation,

  • is really kind of relying on the right ventricle as the pump.

  • And the second one is relying on the left ventricle as the pump.

  • And actually, now that you've seen it, I can now color it in.

  • There it would kind of deliver all the blood

  • to the various organs, and then the organs

  • would use up the oxygen.

  • So let me show it kind of now going back to blue just

  • to indicate deoxygenated blood, and it goes back

  • to the right atrium as deoxygenated blood.

  • So this is kind of how we sometimes see it.

  • And again, this doesn't show you or give you

  • an appreciation for the anatomy exactly,

  • where things branch off and where

  • the different names make sense.

  • But you get a kind of overall feel for the fact

  • that we have two different circulations,

  • and you can see where the blood is

  • going for the two different circuits.

  • Now, when you look at this picture,

  • you could say, well, OK, I guess you

  • can see where all the different tissues are getting the blood.

  • Basically sounds like everything is

  • coming from the oxygenated blood coming out

  • of the left ventricle.

  • But some tissues always kind of trip people up or kind of

  • spark a question, and I'm just going

  • to kind of try to target a couple of the tissues

  • that I think people sometimes might have questions about.

  • And one of them-- wouldn't really call it a tissue,

  • but you could definitely call it a cell type.

  • It's the RBC, and RBC just stands for red blood cell.

  • So people sometimes wonder if the red blood

  • cells are carrying blood to other parts of the body,

  • then how do they themselves get oxygen?

  • Do they just kind of use up some of the oxygen

  • that they're carrying, or what exactly?

  • And to answer this question, I would

  • have to remind you that a red blood cell basically

  • looks a little bit like this in cross-section.

  • And it doesn't have any mitochondria.

  • No mitochondria.

  • So it has no mitochondria.

  • And remember, mitochondria are these tiny little organelles

  • inside of cells that are using oxygen.

  • So if it has no mitochondria, then it

  • is not really using oxygen.

  • So it's not using oxygen.

  • And really, these cells-- we call them cells,

  • and they are in many senses of the word.

  • But they don't really have mitochondria.

  • They also don't have a nucleus.

  • I mean, these are, literally, these amazingly designed cells

  • that are made for the purpose of carrying around oxygen

  • to the body, because they literally

  • are bags of hemoglobin.

  • So just remember, red blood cells don't really need oxygen.

  • They simply carry it around.

  • Another tissue or organ that makes people kind of wonder

  • is the heart.

  • The heart is pumping all the blood around.

  • But does it actually get oxygen from vessels

  • that are in the pulmonary circulation

  • or from the systemic circulation or what?

  • And here, the short answer is systemic circulation.

  • That's kind of the quick answer.

  • And let me actually show you where

  • the blood vessels come from.

  • These are called coronary vessels.

  • I'll just write the word coronary here,

  • coronary vessels.

  • So coronary artery and vein.

  • And these coronary vessels, they actually

  • come right off the aorta here and here.

  • So they kind of come off of the aorta right away.

  • They're the first branches off the aorta, actually.

  • So the first branches go and serve the heart,

  • so it's kind of the first to get systemic circulation blood.

  • And the veins actually drain into a spot

  • directly into the right atrium, so there's actually

  • a little spot right there that they drain into.

  • So the blood from the arterial side is coming from the aorta.

  • And on the venous side, it's actually not

  • even dumping into the inferior or superior vena cava.

  • Kind of a little known fact, it's

  • going directly into the right atrium.

  • And finally, kind of a tricky one, but the lungs.

  • Where do the lungs get their oxygen from?

  • And this is, I say, tricky.

  • And I kind of saved this for last,

  • because there are actually blood vessels.

  • And again, don't worry so much about the anatomy in terms

  • of where is it coming off of exactly?

  • But it's coming off of the systemic circulation,

  • and you've got a vessel going to the right lung.

  • Let's say something like that.

  • And you've got another vessel going--

  • I'll just draw it kind of going--

  • to the left lung like that.

  • So you've got a couple of arteries

  • that are branching off, and these are also

  • part of the systemic circulation.

  • And these are called the bronchial arteries.

  • And these bronchial arteries bring then really

  • wonderful oxygenated blood, right?

  • These are the bronchial arteries.

  • And you might say, well, that wasn't so difficult.

  • I'll say bronchial vessels, because there are also

  • some veins coming off.

  • Actually, let me draw the veins now for you,

  • so you can see how those kind of end up.

  • And these veins, they come from, of course, the right lung.

  • And they actually end up dumping in here.

  • You can't really show blue on blue,

  • but just trust they go there.

  • And you've got another vein from the other lung, kind

  • of following a parallel path and going into the veins as well.

  • And so they don't dump necessarily directly

  • into the inferior or superior vena cava,

  • but I just want to show that they

  • go into the venous side on the systemic circulation.

  • So if that was it, that would be really simple.

  • But actually, lungs are kind of interesting in the sense

  • that there is a lot of mixing going on.

  • So you've got pulmonary arteries carrying blood.

  • You've got bronchial arteries carrying blood,

  • and that blood mixes.

  • And then you've got-- at the capillaries,

  • you've got some blood kind of from both places,

  • the pulmonary circulation and blood

  • from the systemic circulation again mixing.

  • And then on the other side, where the veins are bringing

  • blood back to the heart, most of the blood-- as it turns out,

  • most of the blood actually goes this way,

  • into the pulmonary veins.

  • So even though you have bronchial arteries bringing

  • blood in-- that would be right here--

  • you only have bronchial arteries bringing blood in,

  • a lot of that blood ends up going

  • into the pulmonary circulation.

  • So that's kind of an interesting fact, that not as much goes

  • this way directly into that systemic circulation.

  • So it's kind of a tricky thing to keep in mind.

  • But the lungs, then, technically really

  • are getting blood both from the systemic circulation,

  • but also they're kind of mixing blood.

  • And they're mixing blood with the pulmonary circulation.

  • We'll talk a little bit more about this in another video.

  • I don't want you to feel like this kind of got too confusing.

  • But I just want you to be aware that there is mixing going on

  • in the lungs with the systemic and pulmonary circulation, kind

  • of a neat organ in that sense.

So what you're looking at is basically

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