00:00
Now, here is a little diagram of the
circulation, you can see it’s made in two
colors - blue for the blood that’s returning
to the right side of the heart. It’s exhausted
of its oxygen, it’s carrying waste products,
particularly carbon dioxide. Carbon dioxide
was given off in the lungs, oxygen will be
introduced to the red blood cells and then
they will get to the left side of the heart
where they will be pumped out to the body.
00:25
So, let’s follow the circulation through
the heart. You can see that there are two
large veins here that drain into the right
atrium, the superior vena cava drains the
blood from the upper body, the inferior vena
cava drains the blood from the lower body.
00:43
They both empty into the right atrium and
through… then pass through the tricuspid
valve into the right ventricle, they are pumped
out through the pulmonic valve into the lungs
and then they return through pulmonary veins
to the left atrium and then across the mitral
valve into the left ventricle and the left
ventricle pumps it out through the aortic
valve to the aorta and to the whole body.
What you see here is a small catheter working
its way through the heart. We are going to
talk more about that catheter. That’s how
we measure pressures and the flow, the amount
of blood that the heart is pumping during
a diagnostic catheterization. But, again,
of course, the blood is not exactly this color
blue on the… on the right side of the circulation,
it’s a little bit darker and it’s quite
bright red on the arterial side.
01:37
Now, here is a more anatomically correct diagram
and there are a couple of points I want you
to note about that. You will still notice
the superior vena cava, the inferior vena
cava coming into the right atrium, draining
the... if you will, the deoxygenated or tired
blood into the right atrium. You can see the
tricuspid valve as the blood passes into the
right ventricle and then you can see it being
pumped out into the pulmonary artery, still
all in blue. What’s of interest here is
that the left ventricle is a lot thicker than
the right ventricle. And in fact, their shapes
are slightly different. Why is that? It’s
because they have very different functions.
The pressure in the lung is quite low, so
that the right ventricle functions like a
bellows- like the blacksmith uses to create
air for his fire that he is going to be melting
the… and working on horseshoes, for
example. So, it produces large volumes of
blood movement at low pressure. The left ventricle,
of course, has to pump blood throughout the
body, so it has to pump that blood at a much
higher pressure. And consequently, the walls
of the left ventricle are much thicker than
the walls of the right ventricle, it’s functioning
not like a bellows, but rather like the piston
in a car- a high pressure chamber that does
a lot of pressure work as opposed to the right
ventricle which does a lot of volume work
at much lower pressure.
03:07
Now, here we see the heart diagramed in comparison
to the chest x-ray. You can see on the right
hand side, this is a so called frontal x-ray
like this, and then on the left hand side,
there is a lateral x-ray taken like that from
the side, and what you can see are several
things. First of all, again, notice that the
heart is not in the center of the chest, but
in fact, is a little bit more in the left
chest than the… than the right chest and
the bulge that you see down in the… in the
left chest is actually the left ventricular
outline. If you want to see the right ventricle,
you have to look at the lateral view and you
see it in front of the left ventricle. Now,
people say, “Wait a minute! The heart actually
has the right ventricle in front of the left
ventricle?” And in fact, that is exactly
the case. We will see that on some further
x-rays and Magnetic Resonance Image which
will show you that, in fact, the right ventricle
does lie in front closer to the breast bone
than the left ventricle which lies a little
bit behind. And you can get a hint of that
from the… the two diagrams here that are
reflecting what you see in the chest x-rays
below.
04:26
Now, here is an MRI of the chest. What’s
at the top there is the front, the breast
bone and what’s at the bottom of the picture
is the spine, you can see a little area of
the spinal vertebra there, and you can see
the heart right in the middle there of…
of the diagram labeled; RV is the right ventricle
and LV is the left ventricle and you can
see that the right ventricle is lying in
fact, in front, that is closer to the chest
front wall compared to the left ventricle.
And again, here is again the diagram showing
you where the heart is located and also, where
the different points are that you can best
hear with your stethoscope, the sounds made
by the four heart valves. We are going to
talk about those in… in just a moment. But,
you see their areas on the little bit upper
right chest, little bit upper left chest,
lower right chest and lower left chest.