Flow through the heart | Circulatory system physiology | NCLEX-RN | Khan Academy

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.