WEBVTT

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

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in your body.

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This is the human heart.

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

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

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

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

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in our body.

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

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a little fetus, maybe
about eight weeks old,

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all the way until the
point where you die.

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And so this organ,
I think, would

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

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

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So what I did is I
actually drew what

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it might look like
on the inside.

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So let me actually
just show you that now.

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And we'll follow
the path of blood

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through the heart
using this diagram.

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Let me start with a little
picture in the corner.

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So let's say we
have a person here.

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

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I'm going to draw their arms.

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

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And so the whole
goal is to make sure

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that blood from all
parts of their body,

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including their legs,
can make its way back

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to the heart, first
of all, and then

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get pumped back out to the body.

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

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and dump into there.

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And the same on this side.

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And it's going to
come from their head.

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

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are going to come together
into one big vein.

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

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And then separately,
you've got veins

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from the legs meeting up
with veins from the belly,

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coming into another
opening into the heart.

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

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And any time I
mention the word vein,

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I just want you to
make sure you think

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of blood going
towards the heart.

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Now if blood is going
towards the heart,

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then after the blood
is pumped by the heart,

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

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

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So that's the aorta.

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

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We call it the aortic arch.

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

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this way, a vessel
over this way.

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

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and splits like that.

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So this is kind of a
simplified version of it.

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But you can see how
there are definitely

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some parallels between how
the veins and the arteries

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are set up.

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And arteries, anytime I
mention the word artery,

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

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And an easy way to
remember that is

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that they both start
with the letter A.

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So going to our big diagram now.

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

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in this way is ending
up at the same spot.

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

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

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That's just the
name of the chamber

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that the blood ends up in.

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And it came into the right
atrium from a giant vessel

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up top called the
superior vena cava.

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

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bringing blood
towards the heart.

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And down here, the
inferior vena cava.

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So these are the two
directions that blood

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is going to be flowing.

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And once blood is
in the right atrium,

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

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So this is the right
ventricle, down here.

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This is the second
chamber of the heart.

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And it gets there by
passing through a valve.

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And this valve, and all
valves in the heart,

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are basically
there to keep blood

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moving in the right direction.

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So it doesn't go in the
backwards direction.

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So this valve is called
the tricuspid valve.

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And it's called that
because it's basically

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got three little flaps.

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That's why they call it tri.

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

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

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

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but you can imagine it.

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So blood goes into
the right ventricle.

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And where does it go next?

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

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It's going to go
into this vessel,

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and it's going to split.

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

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

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And it gives you
a clue as to where

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things are going to go next.

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Right?

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Because the word
pulmonary means lungs.

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

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this is my left lung.

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And this is my right
lung, on this side.

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Then these vessels--
and I'll let

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

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

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and left straight.

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This is my left
pulmonary artery.

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And I hesitated
there just to make

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sure you got that because
it's taking blood away

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from the heart.

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And this is my right
pulmonary artery.

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So this is my right and
left pulmonary artery.

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And so blood goes,
now, into my lungs.

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These are the lungs
that are kind of nestled

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into my thorax, where
my heart is sitting.

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It goes into my lungs.

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And remember, this
blood is blue.

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Why is it blue?

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

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

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And so that's one
thing that the lungs

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are going to help me pick up.

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And I'm going to
write O2 for oxygen.

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And it's also blue.

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

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

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And the body's made a
lot of carbon dioxide

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that it's trying to get rid of.

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

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and you pick up oxygen.

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

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

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

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into this chamber.

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So what is that?

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This is our left atrium.

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

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And it goes down into--
and you can probably

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

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

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to the right
ventricle, now we're

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going from the left atrium
to the left ventricle.

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And it passes
through a valve here.

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So this valve is called
the mitral valve.

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And its job is, of
course, to make sure

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that blood does not go from
the left ventricle back

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to the left atrium by accident.

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

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And then the final
valve-- I have

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

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This final valve that
it passes through

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is called the aortic valve.

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And the aortic
valve is going to be

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what divides the left ventricle
from this giant vessel

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that we talked about earlier.

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And this is, of
course, the aorta.

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This is my aorta.

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So now blood is going
to go through the aorta

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to the rest of the body.

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So you can see how blood
now flows from the body

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into the four chambers.

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

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And then it goes into
the right ventricle.

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This is chamber number two.

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

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So this is chamber number three.

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And then the left ventricle.

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And this happens every
moment of every day.

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Every time you hear
your heart beating,

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this process is going on.