hi let's talk about the chambers of the heart in this video we'll discuss the arrangement and
features of the chambers of the heart both the atria and the ventricles we'll discuss pectinate
muscles cordy tindini trabeculae carneae and papillary muscles we'll also discuss
the atrioventricular and semilunar valves how they work and what they're doing during systole
and diastole finally we'll discuss the pattern of connection amongst vessels to each chamber of the
heart where vessels originate and where they go we'll also distinguish between pulmonary arteries
and pulmonary veins so let's start our journey in the right atrium of the heart so blood returns
from systemic circulation largely via the superior vena cava and the inferior vena cava
to the heart also the vasculature that drains the heart of blood the cardiac veins
drain largely into the right atrium as well now the right atrium has a region
into which the vena cavae drain called the sinus venarum the sinus venarum is very smooth walled so
we can see here so this is the superior vena cava this is a portion of the inferior vena cava and we
can see precisely how smooth this wall is we can contrast that with the anterior aspect of the of
the right atrium which is a little more uh rigid with with muscle so in the image here to the right
we're looking at a posterior view of the heart the atrium is open there's the superior vena cava
there's the inferior vena cava reflected away this would be a portion of that opening and we
could see the sinus veneer mole there in this ridge here is called the crista terminalis
there it is crista terminalis and that is the the dividing line between the pectinate muscle
that is anterior to the crista terminalis in the sinus venarum which is posterior
to the crista terminalis that crista terminalis if we follow it to its superior most point here
generally around right there and we go much more superficial so just underneath the the epicardium
we can encounter a cluster of very specialized cardiomyocytes called the sino-atrial or sa node
this is the pacemaker region for the heart one item that we can just barely see here in the uh
the photograph to the uh to the right is the inter atrial septum
that is the wall between the right and the left atria and in in utero
there are two septa or divisions that are slightly separated and the space between these two septa
is called the foramen ovale at birth these septa snap shut and uh they they meld together and so
the foramen ovale is therefore obliterated and that that membranous portion which used to conduct
um relatively oxygenated blood from maternal circulation to the fetal heart is now known as the
fossa ovalis sometimes the a small space of that foramen ovale remains patent or open and that's
referred to as a patent foramen ovale or a pfo in addition we can also see it's right about
there the opening for the coronary sinus the the coronary sinus is the venous sinus into which the
cardiac veins drain and that coronary sinus also drains into the right atrium so superior vena cava
inferior vena cava coronary sinus and some smaller veins will also drain into the right atrium
from the right atrium blood is going to flow through an atrioventricular valve known as the
tricuspid valve into the right ventricle so let's take a look at that now so up here we can see
this has the right and left atria removed we can see the tricuspid valve from above
and there are three cusps to the tricuspid valve there is an anterior and a posterior
and a septal cusp and these three cusps are attached to extensions of the myocardium
called papillary muscles you can see one there one there and one there the ligamentous like
structures that attach to the leaflets of the valves called chordae tendineae these chordae
tendineae are what the papillary muscles can pull upon during ventricular systole such that the
cusps of these valves come into close approximation and therefore blood does not
move retrograde from ventricle to atrium the uh the papillary muscles and the cordy tendineae
while they do apply pressure to the cusp of the tricuspid valve pulling on them is not what
closes the valves it's actually the pressure that builds up in the the ventricles which closes the
av valves the the papillary muscles and the the cordy tendineae they aid that pressure in
approximating the valves and they prevent the the cusps of the valves from from inverting uh back
into the atria but they don't they don't pull the valves closed that's all pressure driven
so as there were anterior posterior and septal cusps of the tricuspid valve there is also
anterior posterior and septal papillary muscles as well and so we can see there is the anterior
there is the posterior and there is the septal cusp in association with that anterior papillary
muscle there is a structure called the septa marginal trabeculae or the moderator band the
septa marginal trabecula was actually first described by leonardo da vinci and there were
various hypothesized reasons for its presence in the heart but we we now know that it conducts
right bundle branch fibers uh across to the uh the right side of the ventricular wall speaking of the
wall of the the ventricle it is very rugos it is very robust with extravasations of
of myocardium pushing the the endocardium in and these are called trabeculae carne or midi beams
and so if you have the opportunity in lab or in cadaveric images to to witness this these
are these are really quite impressive and and beautiful so they are arranged to to help squeeze
the heart during systole they are a nice contrast to the pectin it muscles of the atria which are
much more regularly arranged in in a comb-like fashion and when they help to contract the
ventricles during ventricular systole on the right side blood is propelled
toward the conus arteriosus the conus arteriosus you can see a little bit of it there is a rather
smooth walled portion of the right ventricle and that feeds blood toward the semilunar pulmonary
valve so we can see that semilunar pulmonary valve there the semilunar valves are always
named for the vessels that they are entering into so the pulmonary valve is named for the
pulmonary trunk which then divides into the main pulmonary arteries both right and left
so from the pulmonary arteries which go out to the lungs where blood is oxygenated and carbon
dioxide offloads through the gas exchange of the alveoli oxygenated blood is returned back to the
heart via the pulmonary veins and so um in the in the photo here we can see you know the the left
atrium has been bisected and reflected apart and we can see some of these pulmonary veins there are
there are four sets of them returning blood to the left atrium the left atrium will also have some
pectinate muscle associated with it although it's a little less dense than the right atrium
and there's also the interatrial septum in the fossa ovalis and you'll have the opportunity to
to to see that as well so blood from the left atrium is going to flow through yet
another atrioventricular valve this one called the bicuspid or mitral or mitral because it looks like
a bishop's miter the the bishop's hat so there are two cusps here an anterior and a posterior
which we'll discuss in the context of the left ventricle so here we can see the bicuspid valve
there um there are anterior and posterior cusps associated with uh with this particular valve and
there are cordy tendony attaching those uh cusps of the valve to anterior
and posterior papillary muscles so with two cusps two sets of cordy tendineae two papillary muscles
there are also trabeculae cardi uh we can see them a little better in in this particular image here
as well as the anterior and the posterior papillary muscles of the left ventricle the left
ventricle when it goes through systole is going to send blood superiorly up toward the aortic valve
this is another semilunar valve and the aortic valve enters into the aorta specifically a portion
of the aorta called the ascending aorta and the spaces above these valves
are the aortic sinuses of valsalva so these aortic sinuses which we can see here
so there is one sinus and there is another sinus there there are going to be three of them
but only two of them are going to be coronary sinuses because these feed into the right
coronary artery and the left coronary artery these are the arteries which directly supply the heart
with blood so let's look at what these valves are doing during different stages of the the cardiac
cycle so just as a as a quick review systole is the process of contraction uh diastole
is the process of relaxation so when i think diastole i think dilate and when we simplify
the cardiac cycle into systole and diastole we're referring to ventricular systole because
as you'll recall the cardiac cycle has atrial systole then ventricular systole then diastole
then atrial systole then ventricular systole then diastole so let's look at what is happening first
with those semilunar valves so these are working in coordination with one another both aortic and
pulmonary and you can see here in this illustration that these valves are wide open
they're open during systole because as the ventricles are contracting they are squeezing
blood uh out these aortic and pulmonary valves as we can see there so this is a pressure driven
endeavor as ventricular pressure increases that's going to push blood through the pulmonary trunk
and through the aorta respectively and the pressures within those vessels will also increase
now during diastole as the heart is relaxing and expanding uh pressure is going to be greater in
the pulmonary trunk and aorta than it will be in the ventricles and so the natural inclination of
a fluid such as blood is going to be to be drawn back toward an area of lower pressure well these
cusps of the semilunar valves act as scoops and as blood hits these cusps it brings the cusps
into approximation with one another as we can see here with these closed
caps we can also see a nice right coronary sinus a left coronary sinus and a posterior sinus for the
ascending aorta there now in terms of well i i should also mention that it's
it's during diastole therefore that the coronary arteries are going to
dilate with blood why because as the blood comes back towards these cusps pressure then
is going to force blood through the the coronary arteries so let's discuss what happens with the
atrioventricular valves during systole and diastole so different stages of the
the cardiac cycle so during diastole the av valves are going to be wide open
diastole as you recall is followed by atrial systole so during diastole about 75 of blood
that is destined for the ventricles will flow straight through the atria and the
atrioventricular valves into the ventricles during atrial systole the remaining 25 percent will be
squeezed from the atria and into the ventricles during ventricular systole so just called
systole when ventricular pressure increases that ventricular pressure is going to push upon the
cusps of the av valves to approximate them so they will close therefore the uh the papillary muscles
tugging on the the cordy tendineae are going to help prevent those cusps from prolapsing back into
the atria but you know this is a pressure driven endeavor so during systole we see closure of these
valves and so we therefore can understand why the aortic and pulmonary valves are going to be
open when the atrial ventricular valves are closed because we want a unidirectional flow of blood and
if all the valves were open at the same time then blood would flow into the pulmonary trunk in aorta
with the same amount of pressure that it would flow retrograde back into the atria which would
not be good for the the cycling of blood and that leads us to our assessment question and that is
what structures anchor atrioventricular cusps to papillary muscles are these cordy tendity
the crista terminalis the pectinate muscles the septomarginal trabeculae
or the trabeculae carneae well the correct answer is chordae tendineae cordy tendony
are going to anchor cusps to extensions of the myocardium called papillary muscles the crista
terminalis is the ridge in the right atrium so that is not correct pectin it muscles
are the uh are the myocardial extravasations into the right and left atria so that's not correct
the septa marginal trabecula is that moderator band that connects the ventricular septum to the
anterior papillary muscles that's not correct trabeculae carneae are the irregularly arranged
meaty beams of the myocardium in the ventricles so that is not correct the correct answer is a cordy
tendony anchor atrioventricular cusps to papillary muscles thank you very much for your time