All right. Let?s now take a look at the
individual chambers. We want to understand
the internal features of the individual chambers.
So our first visit or first stop will be with
the right atrium.
So let?s take a look at the various features
of its internal anatomy. So here we?re looking
at the internal aspect of the right atrium.
First thing that you?ll note is a portion
of the right atrial wall internally has some
roughened ridges. And these are muscular ridges
and they make what is known as pectinate muscles.
However, we also have an area to the wall
that?s smooth. The smooth area of the wall
is called the sinus venarum. It is derived
developmentally from the sinus venosus and
it is a vascular structure and, when it gets
incorporated into the wall of the right atrium,
that vascular structure was smooth therefore
its contribution to the formation of the right
atrial wall will also be smooth. Pectinate
muscles are being derived from the primitive
atrium, which is muscular to begin with.
We also have the interatrial septum over here.
Within the interatrial septum, we have this
oval depression. This is referred to as the
fossa ovalis. Understanding the fossa ovalis
is important developmentally. In the embryo,
the interatrial septum at the fossa ovalis
location wasn?t closed off. Instead, there
was an opening between the right atrium into
the left atrium through the interatrial septum.
That opening was referred to or is called
the foramen ovale. And the reason we have
this shunt during development is that you
do not need to send blood through the pulmonary
circulation because the blood is being oxygenated
not by the lungs but by the placental circulation.
So blood gets diverted over into the left
side of the heart from the right atrium into
the left atrium through the foramen ovale.
Then, after birth what will happen is the
valve of the foramen ovale will get slapped
shut against the interatrial septum from the
left atrial side and fuse and then create
this fossa ovalis.
We also have the openings to the inferior
vena cava, superior vena cava. And then we
have the ostium or opening of the coronary
sinus, which is bringing the majority of venous
blood from the heart itself back to the right
atrium. And the last structure to identify
here is the crista terminalis. This is a structure
that separates the pectinate musculature from
the sinus venarum.
All right. Our next stop is the left atrium.
And here we have an internal view of the left
atrium. And if we take a look, most of its
surface is going to be smooth. And it?s
receiving the four pulmonary veins at these
locations. The reason that the wall of the
left atrium is smooth is it incorporates during
development the primitive pulmonary veins.
And again, since those are vascular structures,
the contribution that these vascular structures
make to the wall is to provide for a smooth
internal wall. There is a portion of the left
atrium that is derived from the primitive
atrium, hence it does has pectinate muscles.
And those pectinate muscles are going to be
within the auricle, which we see here of the
left atrium. We can also see this ridge, this
semilunar ridge right in through here. This
represents the valves of the foramen ovale.
And the remnant of the foramen ovale we saw
on the right atrium within the interatrial
wall, the fossa ovalis. But again in the foetal
circulation, the fossa ovalis was open. It
was a foramen and it was called the foramen
ovale. Hence the valve that we see here that
is fused to this area is the valve of the
The right ventricular view is seen here. And,
again, our focus is on its internal anatomy.
And if we look at the internal wall, again
we can see some muscular ridges. So you may
think at first that these muscular ridges
are more robust, more prominent than they
are in the atria, particularly the right atrium.
So maybe pectinate muscles would be used here.
But instead anatomists decided that they deserved
their own unique naming system. And so the
terminology for these muscular ridges in the
right atrium is trabeculae carneae. Trabeculae,
or trabecula for the singular, means beam.
Carneae means flesh. So these are fleshy beams
within the right ventricle.
We also have papillary muscles within the
right ventricle. And attached to the papillary
muscles are tendinous chords referred to as
chordae tendineae. And then they will attach
to the cusps of the valve that we see here.
Also note the thickness of the right ventricular
wall, certainly much thicker than the right
atrium. However, we?ll want to contrast
that to the thickness of the left ventricle,
which is now in your view.
Here we see the internal anatomy of the left
ventricle. It really isn?t any different
than the right ventricle. We have the trabeculae
carneae again and we?ll have papillary muscles
with their chordae tendineae attached to the
margins of the cusps between the left atrium
and the left ventricle. Now take a look here.
You can see the thickness of the left ventricle.
We?ll go back to the previous slide. Here
is the thickness of the right ventricle and,
if we go back to the left ventricle, I think
you can appreciate the fact that the thickness
of the left ventricle is much greater than
the right. And this is due to the greater
pressures that must be generated to force
blood into a high-resistance bed that we find
in the systemic circulation.