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?