Now, let's talk through the pressures
that are in the different parts of the heart.
The reason why this is important is
so you better understand
what the right ventricle,
the left ventricle,
how they are changing
in response to their dynamic environments.
Because the left ventricle is larger,
it has more wall mass
because it has to push blood
throughout the whole body,
versus the right atrium,
has a reduced wall mass
because it only has to push
blood through the lungs.
So, what is blood pressure
returning to the heart at?
By the time it gets into the right atrium,
it’s usually between 0 to 4 mmHg.
And that is the blood coming from
both the superior and inferior vena cavas.
As blood travels through
the right atrium at 0 to 4,
it enters into the right ventricle.
The right ventricle has a systolic
and a diastolic pressure,
just like the left ventricle.
However, its systolic pressure is only 25 mmHg.
Its diastolic pressure is 4 mmHg.
Pushes blood up into the pulmonary artery.
Pulmonary artery pressures are
somewhere around 25 mmHg
and the diastolic is around 10.
You might ask,
Well, then why is diastolic 10 there
when I just said that
in the right ventricle it’s 4.’
Remember, you have semilunar valve
in the pulmonary artery.
So, once you push blood from the
right ventricle into the pulmonary artery,
eventually that valve will close,
and that's going to allow
the right ventricular pressures
to be lower than the pulmonary artery pressures
because of the valve being present there.
When blood returns from the lungs
into the left atrium,
it’s somewhere around 8 to 10 mmHg.
If we look at the left ventricle,
it generates pressures
all the way up to about 120 mmHg
and its diastolic pressure is about 10.
If we look at the systemic circulation,
we’re going to use just the
normal typical numbers of 120/80 mmHg.
That is your systolic and diastolic pressure.
Same thing happens here.
Diastolic pressure is 80,
but if you look at left ventricular diastolic pressure,
it’s only 10.
What is the difference?
The aortic valve.
That valve closes
and keeps pressure in the systemic circulation,
but allows the pressure within the left ventricle to fall.
Why are the systolic pressures matched?
Because that is the force
you’re imparting to the blood
that is leaving the left ventricle
and entering into the systemic circulation.
These pressures set up our
high and low blood pressure circuits.
So, if you think about the left ventricle,
it is in the high pressure circuit.
When it pushes blood out to
the systemic circulation,
this is where we get our 120 mmHg.
The right ventricle,
is in a low blood pressure circuit,
meaning that it receives blood
back to the heart at very low levels,
0 to 4.
It pushes it out only about 20 to 25 mmHg.
So, you can understand why the blood vessels
and the whole structures
associated with these two circuits
are going to be a lot different from each other.
Anything in the high pressure circuit
is going to have to be built in such a way
that it can handle high pressure.
It’s going to have to have more
smooth muscle in the walls of the vesicles.
They're going to have
to have collagen fibers,
so they have higher tensile strength.
Versus low blood pressure circuits,
they can be thinner,
more easily collapsible
because they don't have to
handle such high pressures.