hi let's talk about the heart wall in this video we'll discuss the layers superficial
to deep that one would encounter when cutting through the heart wall we'll also talk about
cardiac muscle tissue and how cardiac muscle cells differ from other types of muscle cells
so the heart wall has three major constituents the epicardium the myocardium and the endocardium
and the heart itself is surrounded by both a pericardial cavity and portions of the
pericardium so the pericardium consists of the fibrous pericardium and then a serous
pericardium and that serous pericardium has a parietal component which is fused
to the fibrous pericardium and then a visceral component which is of the heart
wall itself and the space between the parietal and visceral layers of the serous pericardium
is the pericardial cavity now that visceral layer of the serous pericardium is mesothelial
in nature so it's simple squamous epithelium supported by a basement membrane now this
is riding atop a layer of fibroelastic connective tissue and adipose connective tissue and that
adipose connective tissue which is beneath the epicardium can be quite variable among individuals
and an overabundance of it can be correlated strongly with various metabolic disorders
now also deep to the epicardium is the various neurovasculature which supports
the heart in particular supports the myocardium so the coronary arteries and their branches
the cardiac veins and their tributaries etc and these can most often be found within the sulci
that are a part of the superficial features of the heart now deep to the
epicardium is the myocardium and the myocardium is the most substantial layer of the heart wall
it's principally formed from cardiac muscle tissue but it also has a healthy amount of fibroblasts
and other supportive connective tissue cells to help maintain the myocardium the myocardium of
the atria is distinctly different than that of the ventricles there are physiological
differences between the cardiomyocytes of the atria and the ventricles but on a gross level
the atria tend to be much thinner and the walls the myocardia of the ventricles tend to be much
thicker especially on the left hand side the left ventricle serves systemic circulation the right
ventricle serves pulmonary circulation so you can imagine the differences in pressure generation
that the right has in order to reach the lungs versus the left ventricle has in order to reach
all of systemic circulation now deep to the myocardium is the endocardium which is another
layer of epithelium supported by a basement membrane and you may imagine that the endocardium
is not homogeneous throughout the heart that it is quite different the endocardium in certain
areas will be very smooth in other areas the endocardium is going to take shape around the
myocardium so in the anterior portions of the atria the endocardium will be more pectin it
surrounding the the ventricles um it will be more irregular so we'll have the trabecular carny and
another thing to uh to keep in mind is that any of these layers of the heart the the epicardium
the the myocardium or the endocardium can be the the target of a disease or pathological
process or even injury so we can have pericarditis epicarditis myocarditis or endocarditis and while
all of these etiologies can be very different and the prognoses may be very different among
the the different inflammations of these layers they can all be part of some pathological process
now cardiac muscle tissue is very unique among all of the muscle tissues it is the only muscle tissue
to be branching so an individual cardiomyocyte can can bifurcate or triforce to touch several
other cardiac myocytes they are uninucleate much like smooth muscles much unlike skeletal muscle
and their mitochondria tend to be larger and more numerous than other types of muscle tissues
but probably the the two greatest functions of cardiac myocytes are their intercalated discs
and their propensity toward autorhythmicity and these are related so their intercalated discs
are thickenings of their sarcolemmy and these are areas where two cardiomyocytes are coming
together and there are two novelties here that are of the utmost importance one are the
abundances of desmosomes which are anchors to keep cardiac myocytes together as you can imagine the
heart as an organ beats very early in development and it beats until the the time of death and if a
person is an organ donor perhaps even beyond the time of death and so to to maintain the
connections among the cardiomyocytes is very important the second uh item uh that is of crucial
value to the intercalated disks are the gap junctions gap junctions are proteinaceous tunnels
that allow for the sharing of cytosol between two adjacent cardiac myocytes this connection of the
cytoplasm allows for all of the connected cardiac myocytes to function as one large syncytium so all
of these cells by virtue of the fact that they are connected uh can exquisitely well coordinate
their activities and as action potentials move down the line from one cell to the next ions can
freely flow from one cell to the next now all cardiac muscle tissue is autorhythmic but some
collections of cardiac muscle tissue are more auto than others or i should say they have a higher
intrinsic rate of depolarization so the sa node at the superior aspect of the crista terminalis is is
one such area that has a very high rate of depolarization that serves as the pacemaker
region for the heart now that leads us to the assessment question for this video and that is
what feature of cardiac muscle tissue allows for coordinated depolarization
is it that cardiac muscle tissue is autorhythmic that there are desmosomes gap junctions
large mitochondria or that the cells are uninucleate well the correct answer here are the
gap junctions the gap junctions are what allow for the cardiac myocytes to function as one large
functional syncytium the other aspects here are all true of cardiac muscle tissue but
they do not allow for necessarily coordinated depolarization thank you very much for your time