00:01
Hello and welcome.
00:02
We're going to talk about
something that is very
near and dear to my heart,
which is the cardiovascular system.
00:08
And hopefully it's near and dear
to your hearts as well.
00:12
To really understand the pathology
of heart and vessel,
we really have to understand
the structure and function
relationships.
00:19
And actually, the cardiovascular
system is beautiful in that respect.
00:23
Because if you were going
to design the system,
this is the way you would do it.
00:26
It's very logical,
and it's very physiologic,
and it works terrific.
00:32
And it will last most of us 80-90,
hopefully, 100 years.
00:36
With that preface, let's get going.
00:38
Here's the kind of general framework
roadmap for where we're going today.
00:43
We're going to do an
organization of the vasculature
so understand how vessels are
assembled into a closed circuit.
00:49
We'll talk about the vessel lining
endothelium,
which is actually a whole lot more
important than just a vessel lining.
00:56
And then we'll talk about
basic structures of the heart.
00:59
First up is the organization
of the vasculature.
01:02
We are seeing here a
fairly complex picture,
with the beating heart
centrally as it should be.
01:08
Blood comes in from the
superior and inferior vena cava
bringing blood back
from the entire body
into what's going to be
the right atrium,
the right ventricle,
and eventually it gets
pumped out to the lungs,
and then eventually returns from
the lungs to the left ventricle,
and out the aorta.
01:28
Pulmonary artery is leaving from
the right ventricle into the lungs,
and it's still carrying
deoxygenated blood.
01:35
An important point in the red box
at the bottom,
arteries are not always oxygenated,
and veins are not
always deoxygenated.
01:44
So for example, when we look at
the pulmonary artery,
it is a deoxygenated artery.
01:49
Mainly, we talk about arteries is
taking blood away from the heart
and veins bringing
blood back to the heart.
01:56
So again, not always just
oxygenated and deoxygenated.
02:01
The aortic arch,
the aorta is bringing blood now
out of the left ventricle,
squeezed at
120 millimeters of mercury,
and going out and perfusing
the entire body.
02:13
Going out through
the descending aorta,
and then into the lower organs,
but also perfusing head and neck
and the vessels
of the upper extremities.
02:25
An important kind of
general conceptual thing:
Veins are low pressure.
02:30
They have very high capacitance, about two thirds
the total blood volume
lives in the veins
at any particular moment in time.
02:39
On the other hand,
the arterial system
is high pressure.
02:43
It has to transmit blood
to the entire body
at a pressure sufficient
to move it through tiny capillaries.
02:50
So it's a high pressure system
but low volume.
02:54
Okay, let's get down
into some of the nitty gritty.
02:58
When we're talking about
the high pressure system,
the arterial side,
it's got a certain organization.
03:04
And we're also going to talk about
the venous side,
and it has a certain organization.
03:09
They have the same
general three layers,
but they are put together
slightly differently.
03:15
Let's look now at the left hand side
at an artery, high pressure system.
03:19
Vessels everywhere in the body
are lined by an endothelium,
a simple squamous epithelial layer.
03:27
It sits on top of a
basement membrane,
or a basal membrane,
or a basal lamina.
03:33
They're all synonymous.
03:36
That is then identified
the endothelium.
03:40
And the basement membrane
that it's sitting on
are called the intima.
03:44
This is the innermost layer of
all blood vessels, the intima.
03:49
Demarcating in the
arterial side of the circulation
between the intima
and the next layers
is going to be an
internal elastic membrane,
or an internal elastic lamina.
04:02
That's going to have a little bit
of elastic structure to it,
and be able to expand,
and contract, and recoil.
04:10
That demarcates
the intima from the media.
04:13
The media's just like it sounds,
it's the middle layer.
04:17
It's composed of lots, and lots,
and lots of smooth muscle cells
arranged in a
circumferential organization.
04:26
Demarcating the media
from the most external layer
is going to be the
external elastic lamina
or external elastic membrane.
04:34
This is quite variable.
04:35
It may not be
well defined in many arteries,
but there's going to be
elastic tissue in that location.
04:42
And then outside of that
elastic membrane
is going to be the adventitia.
04:48
The adventitia is going to be
loose connective tissue,
and also have additional structures
including nerve, connective tissue,
and vasa vasorum vessels.
04:58
We'll talk more about that shortly.
05:00
That's the artery,
high pressure, low volume.
05:05
So, the intima,
let's get a little bit more
intimate with the intima.
05:09
It's specialized lining
for all blood vessels.
05:14
The gene expression profile.
05:16
The behavior, the appearance
varies very much in the intima
depending on where you are
in the vascular tree.
05:26
So if you are in the aorta,
it can be quite different
than if you are in the capillaries.
05:33
So the endothelial expression,
the behavior, everything else,
varies depending on where you are.
05:39
And we'll cover that in
more detail in a moment.
05:42
The media. Concentric layers
of smooth muscle cells
that wrap around the vessel lumen.
05:48
And this is going to allow us to
impart contraction, or relaxation,
That will allow us to have
higher pressure or lower pressure.
05:59
There's a very high
elastic content,
also within many vessels,
aortic vessels,
and arterial vessels.
06:07
And that allows us to have recoil.
06:09
We'll talk in a moment about
how the heart is now pulsatile?
And it goes from a
higher pressure to a lower pressure
from systole to diastole.
06:18
And when it goes through systole,
the vessels expand ever so slightly.
06:22
And then we go to diastole,
they contract because
of the elastic content
that allows us
to propel blood forward.
06:32
There's a lot of input from
the autonomic nervous system
in the arterial circulation.
06:37
This is how we control
blood pressure.
06:39
We want to ensure
that we get blood to every last
little nook and cranny of the body.
06:44
And we need to regulate
at a local level
and also a systemic level,
how tight or what kind of tone
the vessels have?
Are they squeezed?
So they have a high tone.
06:55
Are they relaxed,
so they have a low tone?
Out to the adventitia.
07:03
So this contains
the nerve fibers and the vessels
of the vasa vasorum.
07:07
Literally, vasa vasorum means
the vessels of the vessel.
07:12
Some arteries are so thick-walled
that they need to have
their own blood supply.
07:18
They cannot depend on diffusion,
just from the lumen.
07:22
So, we have vessels of the vessel.
07:25
These have vasa vasorum
that will perfuse
those medial smooth muscle cells.
07:32
Again, as already been mentioned,
we may separate the media
from the adventitia
by an external elastic lamina,
that may not always be the case.
07:45
Okay, on the left hand side,
that's the artery.
07:48
On the right hand side,
let's dive a little bit deeper
into the venous structure.
07:53
Veins have the same structure,
just different amounts
of the various components.
08:00
So the endothelium got to be there.
And that's a truism.
08:03
If you don't have
an intact endothelium
you don't have
a happy blood vessel.
08:09
So there's always going to be
endothelium lining
every part
of the cardiovascular system.
08:15
There will be the endothelium
is an epithelium
and it sits on a
basement membrane or basal membrane.
08:22
And then there's going to be
varying amounts of a media.
08:25
Note: It's much thinner, and it's
not going to be as well organized
as the media that we saw
in the arterial circulation.
08:33
There will also be an adventitia.
08:36
Connective tissue that
allows us to kind of organize
the vessel into a tube.
08:41
Alright,
so same general structures,
but there's different amounts
of the various components.
08:51
What does this look like
in real life?
In the lower left hand corner
is an artery, cut in cross section.
08:57
And we can see even from here
that it looks more well-defined
in terms of the three layers
versus the vein which is going to be
in the upper right hand corner.
09:09
We're going to look at each
one of those in turn.
09:10
So this is a low power view.
09:12
This is an artery and a vein
sitting in fat.
09:15
And we're gonna be looking now
at the endothelial cell layer.
09:18
Again, endothelium very thin,
simple squamous, epithelium,
sitting on a basal lamina.
09:25
We have the
Internal Elastic Membrane
that demarcates the intima
from the media.
09:31
We then have the
smooth muscle media
the various layers
are called tunicus
so you can have the tunica intima,
the tunica media,
the tunica adventitia.
09:42
Where you can just say layers,
unless you like Latin.
09:46
And then you have the
External Elastic Membrane
and finally,
we have the adventitia.
09:50
So we have all the various layers
here well demarcated.
09:55
Note: When we look at that artery,
you can see the vessel lumen size.
09:59
Compared to the vein,
it is much smaller.
10:03
This is going to be a
higher pressure system.
10:06
We need to kind of reinforce
the layers of the vessel,
because it's higher pressure.
10:11
And that's why there's
more smooth muscle.
10:14
That's why there's more of a
connective tissue adventitia.
10:18
Now, if we go up to the vein,
there— bigger lumen,
higher capacitance,
greater volume, lower pressure.
10:26
So the wall doesn't have
to be as robust.
10:28
It doesn't have to be as thick.
10:31
Still has an endothelium,
single cell layer,
same deal,
sitting on a basal lamina.
10:36
And then that's it.
That's the intima.
10:39
Now, we're into the
smooth muscle media,
the tunica media,
that layer not as well organized,
not as much as in the artery
because it doesn't have to
maintain the same pressures.
10:51
It doesn't have to.
10:52
It has to actually be
more expansile,
more capacitance
to hold greater amounts of blood.
10:58
And then we're into the adventitia.
11:02
Also shown here is the nerve.
And again, vessels are innervated.
11:07
That's how we can control
to some extent,
the arterial smooth muscle tone,
but also venous tone.
11:16
There are smooth muscle cells there.
11:18
Vein cannot squeeze as hard
as an artery can,
but it can still modulate
how well it squeezes
and nervous input will influence
the tonicity
the tension of how much
the smooth muscle contracts
in either vessel.