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  • So what you're looking at is one of the most amazing organs

  • in your body.

  • This is the human heart.

  • And it's shown with all the vessels on it.

  • And you can see the vessels coming into it and out of it.

  • But the heart, at its core, is a pump.

  • And this pump is why we call it the hardest working organ

  • in our body.

  • Because it starts pumping blood from the point where you're

  • a little fetus, maybe about eight weeks old,

  • all the way until the point where you die.

  • And so this organ, I think, would

  • be really cool to look at in a little bit more detail.

  • But it's hard to do that looking just at the outside.

  • So what I did is I actually drew what

  • it might look like on the inside.

  • So let me actually just show you that now.

  • And we'll follow the path of blood

  • through the heart using this diagram.

  • Let me start with a little picture in the corner.

  • So let's say we have a person here.

  • And this is their face, and this is their neck.

  • I'm going to draw their arms.

  • And they have, in the middle of their chest, their heart.

  • And so the whole goal is to make sure

  • that blood from all parts of their body,

  • including their legs, can make its way back

  • to the heart, first of all, and then

  • get pumped back out to the body.

  • So blood is going to come up from this arm, let's say,

  • and dump into there.

  • And the same on this side.

  • And it's going to come from their head.

  • And all three sources, the two arms and the head,

  • are going to come together into one big vein.

  • And that's going to be dumping into the top of the heart.

  • And then separately, you've got veins

  • from the legs meeting up with veins from the belly,

  • coming into another opening into the heart.

  • So that's how the blood gets back to the heart.

  • And any time I mention the word vein,

  • I just want you to make sure you think

  • of blood going towards the heart.

  • Now if blood is going towards the heart,

  • then after the blood is pumped by the heart,

  • it's going to have to go out to the heart.

  • It's going to have to go away from the heart.

  • So that's the aorta.

  • And the aorta actually has a little arch, like that.

  • We call it the aortic arch.

  • And it sends off one vessel to the arm, one vessel up

  • this way, a vessel over this way.

  • And then this arch kind of goes down, down, down

  • and splits like that.

  • So this is kind of a simplified version of it.

  • But you can see how there are definitely

  • some parallels between how the veins and the arteries

  • are set up.

  • And arteries, anytime I mention the word artery,

  • I want you to think of blood going away from the heart.

  • And an easy way to remember that is

  • that they both start with the letter A.

  • So going to our big diagram now.

  • We can see that blood coming in this way and blood coming

  • in this way is ending up at the same spot.

  • It's going to end up at the-- actually,

  • maybe I'll draw it here-- is ending up at the right atrium.

  • That's just the name of the chamber

  • that the blood ends up in.

  • And it came into the right atrium from a giant vessel

  • up top called the superior vena cava.

  • And this is a vein, of course, because it's

  • bringing blood towards the heart.

  • And down here, the inferior vena cava.

  • So these are the two directions that blood

  • is going to be flowing.

  • And once blood is in the right atrium,

  • it's going to head down into the right ventricle.

  • So this is the right ventricle, down here.

  • This is the second chamber of the heart.

  • And it gets there by passing through a valve.

  • And this valve, and all valves in the heart,

  • are basically there to keep blood

  • moving in the right direction.

  • So it doesn't go in the backwards direction.

  • So this valve is called the tricuspid valve.

  • And it's called that because it's basically

  • got three little flaps.

  • That's why they call it tri.

  • And I know you can only see two in my drawing,

  • and that's just because my drawing is not perfect.

  • And it's hard to show a flap coming out at you,

  • but you can imagine it.

  • So blood goes into the right ventricle.

  • And where does it go next?

  • Well after that, it's going to go this way.

  • It's going to go into this vessel,

  • and it's going to split.

  • But before it goes there, it has to pass through another valve.

  • So this is a valve, right here, called the pulmonary valve.

  • And it gives you a clue as to where

  • things are going to go next.

  • Right?

  • Because the word pulmonary means lungs.

  • And so, if this is my lung, on this side,

  • this is my left lung.

  • And this is my right lung, on this side.

  • Then these vessels-- and I'll let

  • you try to guess what they would be called-- these vessels.

  • This would be my-- I want to make sure I get my right

  • and left straight.

  • This is my left pulmonary artery.

  • And I hesitated there just to make

  • sure you got that because it's taking blood away

  • from the heart.

  • And this is my right pulmonary artery.

  • So this is my right and left pulmonary artery.

  • And so blood goes, now, into my lungs.

  • These are the lungs that are kind of nestled

  • into my thorax, where my heart is sitting.

  • It goes into my lungs.

  • And remember, this blood is blue.

  • Why is it blue?

  • Well, it's blue because it doesn't have very much oxygen.

  • And so one thing that I need to pick up is oxygen.

  • And so that's one thing that the lungs

  • are going to help me pick up.

  • And I'm going to write O2 for oxygen.

  • And it's also blue.

  • And that reminds us that it's full of carbon dioxide.

  • It's full of waste because it's coming from the body.

  • And the body's made a lot of carbon dioxide

  • that it's trying to get rid of.

  • So in the lungs, you get rid of your carbon dioxide

  • and you pick up oxygen.

  • So that's why I switch, at this point,

  • from a blue-colored vessel to a red-colored vessel.

  • So now blood comes back in this way and this way and dumps

  • into this chamber.

  • So what is that?

  • This is our left atrium.

  • So just like our right atrium, we have one on the left.

  • And it goes down into-- and you can probably

  • guess what this one is called-- it's our left ventricle.

  • So just like before, where it went from the right atrium

  • to the right ventricle, now we're

  • going from the left atrium to the left ventricle.

  • And it passes through a valve here.

  • So this valve is called the mitral valve.

  • And its job is, of course, to make sure

  • that blood does not go from the left ventricle back

  • to the left atrium by accident.

  • It wants to make sure that there's forward flow.

  • And then the final valve-- I have

  • to find a nice spot to write it, maybe right here.

  • This final valve that it passes through

  • is called the aortic valve.

  • And the aortic valve is going to be

  • what divides the left ventricle from this giant vessel

  • that we talked about earlier.

  • And this is, of course, the aorta.

  • This is my aorta.

  • So now blood is going to go through the aorta

  • to the rest of the body.

  • So you can see how blood now flows from the body

  • into the four chambers.

  • First into the right atrium-- this is chamber number one.

  • And then it goes into the right ventricle.

  • This is chamber number two.

  • It goes to the lungs and then back out to the left atrium.

  • So this is chamber number three.

  • And then the left ventricle.

  • And this happens every moment of every day.

  • Every time you hear your heart beating,

  • this process is going on.

So what you're looking at is one of the most amazing organs

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