In this section,
we will review the general features of the heart and the
pericardium.
We will emphasize the microscopic and the light
microscopic appearance of cardiac muscle and the
conduction system.
Upon completion of this section,
you should be able to identify the structures listed in
the study guide.
Most of these terms will appear on the screen
as they are discussed.
You should be able to describe the morphology of the
cardiac muscle by light microscopy.
You should also be able to describe the internal
conduction system of the heart.
The bulk of the heart is composed of cardiac muscle
and a small amount of cardiac muscle is also
found.
The attachment point between the vena
cava,
pulmonary vein and the heart.
Cardiac muscle is composed of individual
branched cells with cross striations
and nuclei.
In a central position cardiac
muscle is under the control of the autonomic nervous
system and is therefore considered to be
an involuntary muscle.
This diagram shows the heart in place with
lungs removed.
It shows the sack like covering of the heart known
as the pericardium.
This para cardinal sack is essentially non
dispensable pericardium is
composed of a parietal layer and a visceral
layer.
As shown here,
the parietal layer completely
envelopes the heart.
In the next diagram,
the parietal layer has been cut away
to reveal the reflection
of this layer onto the surface
of the heart as the visceral
pericardium or the epic
RD um
examining the pericardium by low
power light microscopy,
we can see that this parietal pericardium
consists of two layers.
First there is a fibrous
pericardium
and a series
pericardium.
The fibrous pericardium consists of
dense connective tissue
with blood vessels,
nerves and lymphatic
vessels.
I'm changing Now to my 40 x.
objective.
We can now see the
area of the serious
pericardium
with a small amount of
underlying connective tissue and
a covering meself idiom is indicated
by the nucleus.
Now in this area
of the diagram,
we can see that the visceral pericardium has
been partially removed to expose
the underlying muscle fibers
within the myocardial.
The bundles of cells are
arranged in a
regular fashion,
and we will now examine a diagram of the heart
with the visceral pericardium removed.
In this diagram we can see the general
orientation of the bundles of
cells as Early as
1911 Franklin Pain.
Mall suggested that this arrangement of cells would
be the most effective and squeezing blood
from the heart during contraction.
The inter ventricular saugus
has openings for the coronary
vessels that supply
the cardiac muscle.
Let's look at the internal structures of the
heart shown when the anterior wall of the heart is
removed.
The major landmarks of the heart include
the right and left atria,
the right and left ventricles,
the inferior and
superior vena cava,
pulmonary vein
atrial ventricular valves.
The outer epic are ideal
surface,
the middle mile cardi um
and the innermost indoor cardio
surface.
The heart muscle has its own ability to
contract,
but the rate is controlled by a
system of modified cardiac muscle
cells within the substance of the heart
called the conducting system nerve
fibers from the
autonomic nervous system terminate
in a specialized area of the right atrium
called the sino atrial
node.
The S.
A node then controls the rate of
heart contraction throughout the conduction system.
The modified cardiac muscle cells of the essay
node spread throughout
the atrial wall
as the per kenji fibers
and working myocardial
cells.
These connect with the atrial
ventricular node or the A.
V.
Node.
The A.
V cells are also
modified cardiac muscle cells,
which become continuous with
the atrial ventricular bundle
for the common bundle of his.
The column bundle
divides about
into the right and left
bundles and about halfway down the inter
ventricular septum.
The cells within these bundles
enlarge these enlarged cells
are also known as the poor kenji fibers.
The rate of transmission of the impulse
increases in the park in the fibers,
and these bundles of fibers continue to branch
and eventually terminate in
the a pickle portion of the ventricles.
The conduction system is insulated by
connective tissue throughout its length.
Therefore myocardial excitation
takes place only at the termination
of the Perkins.
The fibers.
We'll now examine selected structures in a
gross heart.
We have removed the anterior wall
of the right atrium
and the right ventricle.
As we move down from the right atrium
we see the right atrial
ventricular valve or the
trike.
A spit valve.
The wall of the right ventricle
is thicker in the wall of the right
atrium.
As we move into the right ventricular
wall,
we see ridges which are termed the
Tribeca lee.
Carney bundles of
muscle can be
seen.
These are termed popularly muscles,
these attached to the cornea tendons
which in turn attaches to the lips of the trike.
A spit valve at the
base of the inter ventricular septum.
We can see the an
electrode
implanted in the mile
cardi um through the end of
cardio surface if the essay,
no,
does not function normally.
A pacemaker that uses electrodes like this one can
supplement or control the rate of heart
contraction.
Now,
let's see this section
of the heart wall.
On a slide
for general orientation.
We can point out certain landmarks on the microscope slide
itself.
First note the general
homogeneous appearance
of the muscle within the myocardial.
There are some septal divisions
due to the presence of the paramecium.
This section is taken at the junction of
the atrium
and the ventricle and shows
portions of the atrial wall
with its thickened and no cardio.
We can see the ventricular wall,
the atrial ventricular valve
and the area of the
Angeles.
Fibrosis.
The animus fibrosis is a connective tissue
compensation to which both the atrial
ventricular valves and the cardiac
muscle cells attached.
A branch of the coronary artery is
also seen in the
sub epic Ardian
coronary artery and its branches
penetrates the myocardial.
We will now examine these areas on the light
microscope,
we're now on our scan objective on the light
microscope.
Looking at the atrial wall just
being the atrial cavity.
We see as we look through the atrial wall,
starting from the outside the area
of the epic Rd.
Um the
myocardial
and they thicker indo cardi um
extending from here to here
with its lining
endothelial cells.
As we begin to move down the
atrial wall toward the
ventricle.
We see
first the area of the Angeles
fibrosis.
We see the atrial ventricular
valve.
And as we move back we begin to see now
the muscle within the
myocardial um of the ventricular
wall.
As we move through the
ventricular wall
we see again the branch of
the coronary artery located in the
sub epic are ideal connective
tissue.
And we see
the
branching of the coronary
artery into the
connective tissue.
Septa the perry
mycelium.
As we move down the wall,
we see the
epic Rd um
with its lining muzzle federal cells and
the sub epic cardio.
A real or connective tissue.
Well now I'm moving back
to this area within the Mile Cardi um
showing both cross section
and longitudinal section of Muscle.
We're changing now to our 10x.
objective.
We see
first cross
sections all of the cardiac muscle
cells with their central
nuclei.
Note the nuclear cytoplasmic
ratio
in this area.
We see longitudinal sections
cardiac muscle cells.
With the brian jean
and again
central nuclei.
I'm now going to the oil immersion lens.
To examine this area in greater detail
note the cylindrical shape.
All the cells within this longitudinal view.
Note the branching
here and here of
individual cells.
You can see the week
cross banding
and the positioning of the central
nucleus.
As we move the area,
we can see a capillary
located within the
endometrium with
the original sites located within the lumen.
This is the nucleus
of the capillary lining,
sell the endothelial cell.
At this point
we can see the
presence of the irregular dense structures
known as interconnected desks.
These served as
junctions between individual cells
and are presumed important for the attachment
between cells and for the
transmission of the deep polarization contraction
wave.
This completes the light microscopic study of
normal cardiac muscle cells.
Well now look at components of the conduction
system in the heart.
We're on our 10 X.
Objective.
This is a sino atrial node with a
try chrome stain.
There is an abundance of connective
tissue and a small
number of cells.
The essay cells seem to be distributed
in a somewhat random fashion.
Note the presence of a nodal artery
and branches of same,
which is a landmark for identifying
the S.
A.
Node.
We'll now examine this area on the
oil immersion objective.
We can see the small
size of the fibers.
We can see there is a lighter stained area
which does contain glycogen
And may be responsible for some
distortion of the mile five reels
within the mono fiber.
The next part of the conduction system is
the A.
V.
Node,
the A.
V.
Node and
bundle are demonstrated by a try
chrome stain.
Again,
note the prevalence or the connective
tissue which serves to
insulate the A.
V.
Node and bundle from the
surrounding cardiac muscle
cells.
I'm going to change Now to the 10 x.
objective.
Again,
the atrial ventricular node
and the common bundle.
We can see again that the fibers
are distributed in a
somewhat random fashion.
Will now continue by examining
the per kenji fibers.
This is on low power with a mallory
stain to show first the
Mackenzie fibers
as compared with the normal fibers,
the increased size of the cells
and the lighter steam as compared with the
normal cardiac cells can be
seen.
The lighter stain again is due in
part to the increase in the amount of
glycogen
where now going to move
from the endo cardio surface
into the myocardial.
And again we see the presence
of bundles of per kenji
fibers or cells now
located within the perry mycelium
of the myocardial.
We're moving back now to the endo cardio surface
and we'll be changing to our oil immersion objective
on oil immersion.
Week again,
see the large
Mackenzie cells,
the light staining characteristics
and somewhat Randomly
oriented mile five grills
present within the for kenji
fiber size of these
cells and the light staining characteristic is compared
with the normal cardiac muscle
cell in this
area.
Now,
for review,
let's look at the next diagram
in summary,
this diagram shows certain key
characteristics of cardiac muscle that can be
seen on the light level.
These small elements
represent collagen fibers in the connective
tissue,
which would be considered as a part of the endometrium.
This represents a
capillary within the endometrium.
The cardiac muscle cells,
or fibers are characterized
by a cylindrical shape,
branching
and with central nuclei
and cross dry ations.
Cardiac muscle also has a dense line
which is termed the inter collected
desk.
These desks are the inter cellular
junctions which serve to
attach the cells together and
transmit the electrical impulse from one cell to
another,
brian jean,
and the presence of the interconnected desk
are unique within cardiac muscle
cells.
This concludes the section on light microscopy
of cardiac muscle with a brief description
of pericardium,
epic Rd,
um and endo cardi,
um