so here is the heart with the atria and ventricles so here we have the right atria and this is the
right ventricle and here is the left ventricle and behind that somewhat here is the this is the
left atrium so all these structures are shown in the 3d model of this human heart now what if
we remove the right atrium as well as the left atrium now you can see that this is the right av
orifice right atrioventricular orifice and this is the left atrioventricular orifice and from these
av orifices the valves are protruding actually the cusps or flaps of the valves are protruding
now the right side has a tricuspid valve meaning that the right heart has a valve that has
three cusps while the left heart has a valve that have two cusps why so now an intriguing
mind might compel you to question that why the right side has three cusps and why the left heart
why the left side of the heart has two cusped valve why not opposite that's a logical question
by the way well actually if you want to remember it is just easy to remember you can say that "try
to be right" "try to be right" it means right side has tricuspid three cusped valve and the left side
has bicuspid valve which is also called mitral valve the word mitral it comes from the term miter
miter means a particular shaped hat of a bishop so that is why because it looks like that hat
that is why it is called mitral valve or because it has two cusps so it is called bicuspid valve
now i don't just want you to cram up that right side has three cusps well actually i want you
to understand the logic behind this i want you to have the basic concept so in today's
video lecture we will talk about that why the right heart has tricuspid valve and not bicuspid
valve and vice versa hello i am dr Aizaz from medicovicial.com welcome to this visual lecture
now if you just focus on these av orifices you can easily see that the right av orifice the av
orifice of the right heart is relatively larger relatively much larger as compared to the left
av orifice now actually if i tell you some boring numbers if you let's say take a meauring tape and
if you start meauring like this starting from here and continue and if you meaure the circumference
of this av orifice like this the circumference of this av orifice according to grey's anatomy in
males is 11.4 centimeter in females it is slightly lower and compare this with the circumference of
left av orifice which is just on an average which is just 7 centimeter so what you can see that the
circumference of left av orifice is much lesser as compared to the circumference of right av orifice
so right av orifice is larger as compared to left av orifice of course the diameter of these av
orifice is also different the right av orifice its diameter would be greater as compared to that left
av orifice but because of their irregular shapes it is difficult to determine the diameter so
rather than putting the diameter we simply tell about the circumference of this av orifice now one
simple reason for the presence of tricuspid valve the three cursed valve in the right heart is that
the av orifice of the right heart is bigger valve simple as that the av orifice is bigger
on the right side so to compensate for that we might need an extra cusp an extra flap so that
is why the right heart has three cusped valve now this explanation might breed another question in
your mind why the heck the right av orifice is bigger as compared to the left aviorifis
well again that is a logical question actually there must be some reason for this you see
everything in our body is purpose built and the heart is epitome of such intelligent design
so today we will dive a bit deeper into the sea of physiology as well to understand the concept
now if you look at the shape of these ventricles this is the right ventricle
you can easily see that the right ventricle it is somewhat triangular shaped so here you can see
that the shape of right ventricle is triangular so it is somewhat like this this is here is the
base this one is the base of that triangle and this one is the apex opposite to that the
left ventricle it is somewhat tubular or it is somewhat tube shaped or bullet shaped
so it means that because the right ventricle is triangular shape so this is the base of that
right ventricle and the base of right ventricle is naturally much wider as compared to the tube
shaped left ventricle and because the base of this right ventricle is wider that is why the right av
orifice is wider and because right av orifice is wider we need an extra cusp to compensate that
so that is the reason that we have tricuspid valve that is most probable reason of course we are not
100 sure but that is the most likely reason now another question that why the right ventricle
is triangular shaped and why the left ventricle is shaped more like a tube to understand this
i am gonna hide everything and we will go to a more simplified 3d model of the heart
so here we have a more simplified 3d model of the heart and here we have left ventricle this
red one and this blue one is the right ventricle and again here in this diagram as well you can see
that you can see it more clearly although this diagram is not anatomically correct but it will
help you understand the physiology and dynamics of these chambers of heart so here you can see that
the left ventricle this is the left ventricle here this left ventricle is shaped more like a tube
or bullet shaped while the right ventricle it is shaped like a triangle and of course the base of
triangle is much wider and that leads to a greater diameter and circumference of orifice on the right
side the second thing that you might have noticed in this 3d model that the walls of left ventricle
they are much thicker as compared to the walls of right ventricle the reason is simple that
because the left ventricle has to pump the blood throughout the body and it needs to build much
greater pressure because it has to pump against a greater resistance so because it has to work hard
so it is more muscular it is more powerful chamber opposite to that the right ventricle does not has
to pump the blood throughout the body rather it has to pump the blood only to the lungs which are
lying very near and dear to the heart so and of course they offer less resistance to blood flow
so because right heart right ventricle has to do much less work so its walls are thinner as
compared to the left ventricle and because the walls of right ventricles are thinner it
means that it has more space to accommodate the blood its lumen is greater as compared to the
left ventricle left ventricles lumen is smaller as compared to the right ventricle wall actually the
left ventricle is slightly bigger than the right ventricle if you see externally the left ventricle
is bigger than the right ventricle but if we talk about the lumen of the ventricles then the
right ventricle has a greater lumen has a bigger lumen while the left ventricle has a smaller lumen
and of course because of this the surface area of the lumen of right ventricle is greater and the
surface area of lumen of left ventricle is lesser it is smaller why it is so this is because the
right ventricle it has to produce less pressure it has to produce less pressure but left ventricle
because it has to pump the blood against a higher resistance throughout the body it has to produce
greater pressure now imagine two balloons one balloon is smaller and the other balloon
is larger now if you fill both of these balloons smaller as well as larger with the same volume of
water which balloon will have greater pressure inside it the answer would be that the smaller
balloon will have build up a greater pressure inside it because the surface area is less the
ratio of surface area to volume is much lesser in case of smaller balloon but because this
larger balloon has a greater surface area it can accumulate more fluid it can accumulate more water
without exerting too much pressure on this water now let's assume that this is not the balloon
this is the right ventricle and this is the left ventricle now because right ventricle has a wider
lumen it causes less buildup of pressure inside it while the left ventricle it causes a buildup of
high pressure inside it its wall exert greater pressure on the blood while the walls of right
ventricle they do not need to generate too much pressure so they exert less pressure on the blood
now the second thing is that why this particular shape of these ventricles why the left ventricle
is shaped like a triangle the reason lies in the dynamics of both of these chambers this
concept has been pretty nicely elaborated by walter f boron in his book medical physiology
and i will explain those concepts using the 3d illustrations and 3d animations
right ventricle has this somewhat free wall and this wall is somewhat fixed now this free wall it
moves like this and this leads to a generation of less pressure but a good volume of blood
will be pumped out as a result of such contraction opposite to that if we focus on the left ventricle
left ventricle has a lot of circular muscles and what these circular muscles will do that
they will contract in such a way that the diameter of this tube like left ventricle will be reduced
and it is just like squeezing a tube of toothpaste while the contraction of right ventricles
is like the movement of bellows that are used to air the fire so let's see the
animation first here you can see that how this free wall it will come to meet a relatively fixed
wall in case of right ventricle and in case of left ventricle the diameter is being reduced
now you can see the movement of right ventricle is just like those bellows that are used to air the
fire and the movement of left ventricle it is just like the squeezing of toothpaste from the tube
so that is basically it that's why the right side of the heart has a tricuspid valve it is
very simple the right av orifice is greater while the left av orifice is smaller and why it is so
that i have explained in a great detail i hope you learned something thank you so much
for watching this video and if you like this video please check out my course on development
of cvs the cvs embryology course you will love that course