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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.
