Comprehensive Guide to Heart Development: From Heart Tube to Valves

all right ninja nerds in this video we are going to talk about the development of the heart before we go ahead and get

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let's get into it all right ninja nurse what we're going to do is we're going to talk about the

development of the heart but in order for us to do that we're going to do this in kind of like sections

the first thing that we're going to try to do is develop a heart tube okay one singular heart tube

and then surrounding that heart tube we're going to try to develop what's called a pericardial cavity

okay so that's the goal so in order for us to do this we have to start with this top of the diagram and we're going to

work our way down doing two different types of folding process don't worry i'll explain it to you

the first thing i want you to look at here is the top of the embryo right when you're looking at the top or the

superior view of the embryo first thing i want you to remember here is you have two

portions of this embryo this portion here very simply is the cranial aspect of this developing embryo and

then this portion down here is the caudal aspect of the embryo another way of saying this is this is

the head and this is the tail of the embryo it's pretty simple right well if you guys remember

during the gastrulation process remember cells from the epiblast are moving down through that primitive shriek right

we have the primitive streak right here and the primitive node right there if you guys remember some of these

epiblast these blue cells are moving through the primitive streak and when they move through that

primitive streak do you remember what they do they convert the hypoblast if it's a

bileminer disc it turns the hypoblast into the endoderm and then it makes a new layer between

this blue layer called the epiblast and the new endoderm layer which is going to be called the

mesoderm that mesoderm is going to be sandwiched between the ectoderm and the endoderm what i

want you to understand out of all of this though is that a collection of mesoderm really

starts to kind of take its place in the cranial aspect of this developing embryo right so

you're going to have kind of this really interesting mesoderm clumped here in the cranial aspect of the developing

embryo in front of your procoral plate so technically what i want you to gain from

this is the heart actually develops in the head and then it starts to move down into the

thorax we'll talk about that and you'll see that best with this type of view here with the sagittal view what i

want us to do is look at this actual development of the heart tube in two views one is we're going to

look here in the cross-sectional view so we're going to kind of take like this okay and we're going to look

at it here in this cross sectional view okay and this is going to be very very

important i really think this view is really really important

the next thing that we're going to do is we're going to take and look at the actual development of the hardtube

from a sagittal section so we're going to take a sagittal section here so now we're going to be doing is taking

a look at this in a sagittal section sagittal sections are good for being able to see the movement or the

migration from the head into the thorax all right so we have two sections here that we're going to be

kind of looking at to understand the development of the heart tube cross section and a sagittal section

let's start here with the cross section when you take this cross section this one here so we'll number it just we

understand this is the first section which we're going to be talking about here

and this is the second section which we'll be talking about over here when you take a cross section and you're

looking at it after gastrulation has occurred you have three layers here this layer

here is your ectoderm this layer here in the middle is your

mesoderm and this layer here on the bottom is the endoderm or the blue is the ectoderm the red is the

mesoderm and the green is the endoderm when you look at it you have

particular particularly this mesoderm is the area that we really want to focus on when you're

looking at it you have three components of it this one here which is next to this called the

notochord this is actually called your par axial mesoderm okay

this one here which is just lateral to it is called your intermediate mesoderm

and this one over here both of these sections this one kind of coming up here and this one going down there

this is what's called your lateral mesoderm your lateral plate mesoderm if you will to kind of give you guys an

understanding here this part of the ladder plate mesoderm is called your somatic

and then this one here is called your splank nick layer of the lateral plate music

what i want you to understand is the heart tube develops from the splanchnic layer of the lateral

platenessiderm so when we're talking about this mesoderm up there really the mesoderm

that i really want you to focus on that is the cardiogenic area is this splenic layer of the lateral

plate mesoderm here's something very interesting that happens this endoderm starts secreting lots of

growth factors so it starts secreting lots of growth factors that are going to try to

influence this splenic layer of the ladder play music and what are these growth factors that

it's releasing it's releasing a lot of what's called vascular

endothelial growth factors vegf is another way that we kind of refer to it

and what vegf does is it stimulates the lateral plate mesoderm to kind of start differentiating and specializing if you

will what does that mean let me explain let's say imagine here that we're just taking the mesoderm

okay so here's our mesoderm okay a clump of mesoderm the vascular endothelial growth factor

are going to do something very interesting where it's going to stimulate this mesoderm to kind of

differentiate and when it differentiates it actually kind of does two things one

is it forms this outer core and then one is it forms this kind of inner core

the outer portion is going to become what really will become our blood vessels and our heart tube

okay and we call this outer portion here we actually are going to call this the angioblast cells

okay your angioblasts and then the inner part which will become our blood cells our reds

red cells white cells all that stuff this is technically what we call the hemo cytoblast

so what vegf is doing is is it's causing the mesoderm to differentiate into what

blood vessels right and actually the heart tube itself and blood cells now

let's actually take a look and see how vegf actually influences the latter plate mesoderm in the next step so what

we had here was ladder plate mesoderm vegf was stimulating it causing it to differentiate make heart tubes

now take a look here you see how from the lateral plate mesoderm this actual chunk of mesoderm grows off

of it and it starts specializing and you form little cavities

what are these cavities here this cavities right here these are called your heart tubes

these are called your heart tubes and then these cavities here that are in the back

these are called your pericardial cavities these are called your pericardial cavities

so from the lateral plate mesoderm what did we do we released vegf stimulate the ladder plate mesoderm to

form heart tubes and a little cavity starts to develop within that lateral

plate mesoderm and these are called your pericardial cavities now what happens is this embryo imagine

these edges i'm going to start trying to bring them closer to one another so i'm going to

bring this ectoderm layer cause it diffuse together bring the mesoderm layer cause it to fuse together

and bring these two edges here together when i do that guess what happens these heart tubes are

going to fuse together and make one singular heart soup so two hard tubes come

together and make one heart tube these pericardial cavities whenever

these two edges come together they fuse and takes two pericardial cavities and makes it into

one pericardial cavity and we'll just keep going here where did that actual green part you

know what this green part is actually where he said that the endoderm right the endoderm

will make the epithelial lining of the gi tract that's going to get invaginated more

posteriorly and look there's the actual endoderm lining which will become the the epithelial lining of

our gi tract so that's that step okay so we took the lateral plate mesoderm stimulated it

with vegf formed heart tubes pericardial cavities during the lateral folding the heart

tubes pericardial cavities fuse become one heart tube one pericardial cavity

one more thing that we have to understand you see we have the heart tube kind of sitting in the pericardial

cavity well it doesn't just sit there without you know it's going to just flop around

we can't let that happen we have to kind of like hold it against this actual posterior wall a little bit

and so what happens is some mesoderm connects the pericardial cavity to the heart tube what is this structure here

called this is called your dorsal mesocardium so this is called your

dorsal mesocardium okay so we have our dorsal mesiocardium which is

connecting the pericardial cavity to the heart tube let's now zoom in on the heart tube a

little bit so let's just kind of focus on the pericardial cavity and the heart tube

so again here's the pericardial cavity here's your dorsal mesocardium when you look at the heart tube the

heart tube is actually made up of a couple layers the most inner aspect of the heart tube

this red part this is actually called the endocardium it's made up of those endothelial cells

which we developed from what from the mesoderm right we said that the mesoderm gets stimulated by vegf and

makes angioblasts and we also said hemocytoblast the angioblasts are what's going to become

the endothelial lining and make the endocardium on the outer part here this blue layer here

this blue layer is called the myocardium this is called your myocardium

and your myocardium is actually developed from cardiac myocytes so this is cardiac

myocytes now what's very interesting is that these cardiac myoblasts

they start secreting kind of a little connective tissue or jelly-like substance which forms between

the endocardium and the myocardium what is that pink like jelly substance which is made by the myocardium

that is called the cardiac jelly not even joking it's called the cardiac jelly

okay so what we've done up to this point is we started with lateral plate mesoderm stimulated with

vegf made two heart tubes two pericardial cavities from lateral folding we fused the two

heart tubes made one heart tube fused the pericardial cavities made one pericardial cavity

suspended the heart tube in the pericardial cavity by the dorsal mesocardium

and if we zoomed in on the heart tube and looked at the layers the inner layer is the endocardium which

is made from the angioblast and then you have the myocardium on the outside which secrete a substance called

cardiac jelly which sits in the center boom we hit this from the cross-sectional view

now let's take a look at this from the sagittal view alright so we took and looked at the development of the heart

tube from what in a cross-sectional view undergoing lateral folding now let's talk about the development of the heart

tube in the pericardial cavity in a sagittal view as it undergoes cranial caudal

folding so if we take a look here again we're looking at this section here we're

looking at a sagittal section and again we kind of numbered that too so first thing we have here is our

sagittal section obviously up here in blue is your ectoderm here is your

endoderm right now what i want you to remember is we're looking at this in front of in the top

in the cranial most portion so here is that actual cardiogenic area or that clump of mesoderm

which would become the heart tube so right here is your clump of mesoderm that is going to become the actual heart

tube so this is basically your mesoderm which will become the heart tube

now what we're going to do is we're now that we understand that they're actually oh one more thing here you know how in

between here between this actual portion here there's a little membrane which is kind of

connecting this cardiogenic mesoderm to the ecto and endoderm you know what this little can

like little stalk is here that's called your buccopharyngeal membrane that'll actually become the

opening right the stimodium will become the mouth now what happens here is that this mesoderm

starts to undergo the differentiation process right how remember what the endoderm does it

releases vegf vagef will then stimulate the mesoderm to do what

start to form angioblasts which would become kind of the endocardial lining help to form like pretty much your heart

tube and then inside of that heart tube the other parts of the mesoderm will become

your blood cells your hemocytoblasts so now go on to the next step veg f stimulated the actual

mesoderm here to start differentiating now look what we have here still same thing here we have our

ectoderm we have our endoderm and again remember this is the cranial portion where the actual

cardiogenic center is this is the caudal portion now the next thing you need to notice is look what

happened it's no longer just one clump of mesoderm here on the top you see how this is all dark

this dark portion here is what's going to become that is the heart tube and then this here that's actually kind

of like a little cavity that is going to be the pericardial cavity so it's kind of it's

the same process in the actual cross-sectional view

but you're just looking at this as it folds something different happens and i'll explain it

so ectoderm endoderm endoderm releases vegf stimulates the actual mesoderm to differentiate

forms a heart tube and a pericardial cavity here's where it gets really cool the ectoderm and endoderm start folding

so they start folding it at the ends right so the cranial end starts kind of turning in

and the caudal end starts turning in as it does that it pulls this mesoderm structure

towards the actual bottom part it pulls it caudally so then what happens is it moves from

the head kind of a little bit more to like maybe the neck area so now it's kind of towards the neck

area as it continues to keep folding so now we have our embryo kind of folding here

look where it actually goes it completely turns in here and goes into your actual chest cavity

so during this process of what's called cranio caudal folding what is actually

happening you're actually moving imagine like this is the best way i think to imagine

imagine your heart is developing above your head as you start kind of folding as the baby is actually folding

the actual heart is moving inwards in front of the face in front of the neck

and into the thorax that is what you're seeing in this sagittal section now one more thing

remember how we had the heart tubes fuse pericardial cavities fuse and basically the heart tube formed

in the pericardial cavity the same thing has to happen here so what happens is here

you're going to have your pericardial cavity during this cranial caudal folding guess

what it does it kind of pulls the actual heart tube into the pericardial cavity

so now here's my heart tube sitting in the pericardial cavity before during this actual process they were separated

but during the craniocaudal folding as it moves from the head over the face over the neck and into the

thorax the heart tube gets stuffed into the pericardial cavity so that is what i want you to understand

the last thing that we have to do here is what i want you to do is take the heart tube

from this cross-sectional view take the heart tube from the sagittal view and let's yank it

out and look at it and it's lengthwise what it actually looks like in all the different kind of vesicular

portions so let's say that we take this heart tube here we're just gonna for right now

abbreviate them we'll kind of denote them a little bit later in what they become

but i want you to kind of know this is the top of the hard tube and then as we kind of go work our way

down this is the bottom of the heart tube at the top of the heart tube you have

these little things that are coming off here these are basically going to be your outflow tracks so

blood will actually come in from the bottom and then leave out via the top okay these outflow

tracks are basically your dorsal aorta okay these are called your dorsal aorta

okay so same thing over here i'm going to abbreviate a dorsal aorta right the dorsal aorta come from this

area here at the top called the aortic sac but really this portion here at the top most top

portion here we're going to abbreviate this ta this is called your truncus arteriosus

what i really want you to know is the truncus arteriosis really makes up the top of the heart tube

below the truncus arterios this is what's called your bulbous cortis okay below the bulbous cordis is

what's called your primitive ventricle below the primitive ventricle is the primitive atria and below the

primitive atria is what's called the sinus venosus and then again blood will come

in via the sinus venosus through the primitive atria through the primitive ventricle through the bulbous

cortes through the truncus arteriosis and out through the dorsal aortae

so you kind of already start to get an idea of what some of these structures will

become with respect to the adult heart all right so we've formed our heart tube we've denoted the portions of it

let's really dig into it a little bit more and talk about what these actual components become

all right ninjas we've formed our heart tube we've accomplished this we know that the heart tube is coming from the

lateral plate music and particularly the splanchnic portion of the lateral plate mesoderm we know that it's under the

influence of vegf we finally made it now let's go back let's denote these different portions

right what did we kind of abbreviate them as just real quick here remember this was the aortic sac

right so the top part here is going to be what's called the aortic sac and we said that the aortic sac goes

into what what structure does that actually fill into we said that it actually leaves out

via what structures it'll leave via the dorsal aorta right then below

the aortic sac what was the next structure this was the truncus arteriosus so then we have the

truncus arteriosus here's what i really want you guys to know the truncus arteriosus

is what becomes the pulmonary artery and the aorta so the truncus arteriosus is what becomes the pulmonary trunk

which is pretty much going to make up your pulmonary arteries and your aortic arch okay

so first thing i want you to know truncus arteriosus becomes those two structures

what is below this what do we say the bulbous cordis all right so this is called our bulbous

cordis now what does the bulbous cordis become this becomes the right ventricle right

so this becomes the right ventricle and the right and left outflow tracks so it's the actual

outflow tracks from the right ventricle and the left ventricle very very important okay

beautiful the next structure here below the bulbous cord is here in pink is what

the primitive ventricle so this is called your primitive ventricle it's obvious what this is

going to become this was the right ventricle in the outflow tracks what do you really have

left ventricle wise this is going to become your left ventricle the next thing

below the primitive ventricle is going to be the primitive atria it's obvious what these will

become the primitive atria is going to become both the left and right

atrium it's going to become the left atrium and the right atrium the last portion here

below the primitive atria is called the sinus venosus before we kind of write that down though

the sinus venous as we said has inflow right so there's these are the inflow tracts we'll name these in a little bit

but there's three inflow tracts entering into the cytospinosis via this horn and this horn

this is going to be the right horn of the sinuspinosis and this is going to be the

left horn of the sinus venosus but the the names of the veins that are actually entering into it

are the same so again what is this structure here called it is called the sinus venosus now coming in

via these horns what are the names of the veins that enter into it you have the common cardinal veins so

you have what's called the common cardinal veins and then generally that's going to be

the ones that are on the most outer part okay then if you come inwards you have the umbilical veins

so then you'll have the umbilical veins and then as you become the most inward these will be your vitelline veins

these will be your vitelline veins beautiful so now do you remember how i told you that

once you kind of have an understanding at this point it's pretty easy that blood is coming in via these veins

into the sinus venous which will empty into the primitive atria go to the primitive ventricle

go to the bulbous cortes which is pretty much going to make your outflow tracks that'll then spit that out into the

pulmonary trunk into the aortic arch and then eventually you'll you'll have what's called the aortic sac and the

dorsal aortic right now does this look like what a heart looks like no

so now what we have to do is there's a process called cardiac looping so now what we have to

do is go through a process called cardiac looping which is annoying as all crap

but what i really need you guys to take away from this is the reason why cardiac looping is

important is it depends upon particular types of proteins called dyneins okay and if these dyneins are absent

it can lead to what's called cardiganer syndrome and this is basically where someone can

have they either have absent cilia but the big part here is that the heart doesn't actually loop

properly and form properly you know what happens it actually doesn't normally for a

normal person the heart will kind of actually bend kind of two thirds to the left of the midstern line

if you have some type of dish issue with these dyneins guess what happens the art doesn't

actually bend to the left it bends to the right and this can lead to dextrocardia or

sometimes what's called situs inversus okay so it's important to understand why cardiac folding

is important because you need these dyneins to allow for that to occur all right nonetheless what i want you to

take into consideration here is we're going to start this cardiac looping process

let's kind of denote these just the truncus arteriosus here right trunk is arteriosus this is our

bulbous cortis this is our primitive ventricle this is our primitive atria

and then here at the bottom you'll have your sinus phonosis okay what i want you to know here is that

what happens is that the the truncus arteriosus and the bulbous cortis start kind of like

moving to the right and downward so the first part of cardiac looping is the truncus arteriosus and the

bulbous cortes kind of start moving downward and to the right

all right so truncus arteriosus and bulbous cordis move down

and to the right and by doing that you start to get this configuration okay

then what happens is the bulbous cordis and continues to kind of move downward the

truncus arteriosus continues to kind of move downwards and to the right but then the primitive

ventricle starts to move towards the left of the midline

so now the primitive ventricle is going to start moving to the left of the midline so now look what happens

as that happens the truncus arteriosus bulbous core to start moving a little bit towards downwards and to the right

so you get this kind of configuration here the primitive ventricle is going to move

left of the midline so then this is going to be your primitive ventricle and the primitive atria actually kind of

gets sucked into the back they start kind of moving backwards so then back here you're going

to have your primitive atria and your sinus phonosis with your inflow tracts right

now here's what i want you to understand because it's very difficult to imagine this you're

looking at this from kind of a frontal view okay so you're looking at this kind of head-on

if i were to take this and turn it where you were looking at this from a side view

you would get kind of something like this so remember what connects the primitive what

connects to the primitive atria above the primitive ventricle so here let's have kind of the primitive ventricle

here and what happens is here we'll have bulbous cordis primitive ventricle

and then coming here backwards is going to be your primitive atria and then coming off of that is going to be

your sinus phonosis right so what you actually see here is when you're looking you're looking at

this view the primitive atria is actually going to start moving

backwards and then upwards so the primitive h will move backwards and upwards

and then look what happens here all right so we understand right with the primitive atria it has to move where

it moves backwards and then it starts moving upwards right so as it starts to move backwards

and upwards they start to pop up over the bulbous cordus and the primitive

ventricle so now you have the primitive atria here right you still have your truncus

arteriosus you have your bulbous cortis you have your primitive ventricle here

right and then again you can't see it but again what will be coming off of the primitive atria coming behind

this this is going to be the sinus venosus right so it's starting to somewhat look

like a heart right because the primitive ventricle will become the left the perimeter of h will

form your right and left atrium your bulbous cortis will form the right ventricle and then the outflow tracts

and the truncus arteriosis will make the pulmonary trunk and the aortic arch right so we're

starting to get some of this view now what happens is you got to remember as this cardiac looping is occurring is

actually kind of occurring inside of this pericardial cavity here so what i want you to think about here

is we have this type of pericardium here right this is our pericardium

okay and you have the pericardium you have the different portions of it right like you have the outer fibrous

pericardium and then you have the inner what's called parietal pericardium don't worry about that right now

what i do want you to understand is is that if you guys remember you had that structure here called the sinus

venosus right the sinus venosus does two very interesting things

it starts to actually allow some of the cells within this area to move into the pericardial cavity

and as it moves into the pericardial cavity it starts to form around the heart

okay and as it starts to form around the heart you start to get this layer underneath of the pericardium what do

you think this is called that's called your visceral pericardium so the sinus venosus

is giving way to what structure the visceral pericardium all right

one more thing that i also think is important in the beginning weeks like week four

week six some of the cells of the sinus venosus even infiltrate into the heart

and start to form some small like primitive conduction system that allows for the heart to start

beating and you can detect that on transvaginal ultrasound around week six so not only does the sinus venous give

way to the actual visceral pericardium but it also gives way to what's called a primitive kind of conduction

system that can be detected during the gestational development all right cool now we've taken and

developed our heart tube we looped the crap out of it we formed it inside of the pericardial

cavity we layered it with a visceral pericardium and now it's starting to even have a

little bit of a primitive beating type of activity now what i really want us to do is to

take these primitive atria right and then your primitive ventricle and your bulbous cordis

and really start developing septations or forming chambers that separate the atria

from one another and separate the atria from the ventricles that's the next step

let's do it all right so now let's go ahead and take and start kind of first forming the next goal we formed

the heart tube we looped it we put in the pericardial cavity we made some layerings we have

some conduction the next goal that i want us to accomplish here

is to actually form um what's called an two av canals in other words a canal between the atria and the ventricles

both a right av canal and a left av canal that's the first goal

let's do it so if you guys remember what was the structure here you guys will know this by the end right so truncus

arteriosus bulbous cortis primitive ventricle primitive atria

sinus venosus there's actually a little sulcus between the primitive atria

and the perimeter ventricle so right here i'm coming through that little sulcus there

that's called your av sulcus i'm making a section right here between the primitive

atria and the primitive ventricle what i want you to imagine is when i make this

cut this is what we're looking at we're literally looking at the inner aspect of the heart tube

okay this is going to be the posterior portion of the heart tube and this is going to be the anterior

portion of the heart tube now the next thing i need you to imagine out here coming at you like it's coming

out into actually hit you in the face is going to be the primitive atria okay then going

into the board is the primitive ventricle okay so you're looking at the posterior

anterior portion and this view coming out primitive atria going in

primitive ventricle what i need you to first understand is is that you guys remember those pesky

little neural crest cells i know you guys do those pesky little neural crest cells

start actually kind of migrating here so here we're going to draw a couple neural crest cells

so here's some neural crest cells those neural crest cells will start migrating into this area

and start forming little kind of like cushions that come off the posterior portion

and that come off of the anterior portion so these neural crest cells are going to

move in here and they're going to start forming like little cushions okay what are these things here called

they're called endocardial cushions these would be your anterior endocardial cushions and this would be your

posterior endocardium collisions right so here we'll put here endocardial cushions endocardial cushion this would

be the post here that would be the anterior as these endocardial cushions coming

from the neural crest cells continue to grow grow grow grow grow guess what they do they fuse

together and when they fuse together something very interesting happens

where you start to develop two little canals right so now i have a little kind of like canal here

a little canal here and a little canal here and what was above here primitive atria what was going into the

board primitive ventricle that's very interesting we'll talk about what that is in just a second but what i

do need you to know is that when those endocardial cushions come together and fuse

they make a special name we got to give it a special name this is called the septum

intermedium so the septum intermedium is the structure that is formed when the posterior and anterior endocardial

cushions from the neural crest cells come together and fuse when they fuse they now beautifully

separate the primitive atria and the primitive ventricle and form two little canals

what are those little canals okay let's do it again here's our septum intermedium formed by

those other cardio cushions coming together and then here on one side

of the septum intermedium is going to be an av canal this one here is called your right

a v canal and this one here is called your left av canal so now i have

a separation of some form between the left side of the heart in some ways and the right side of the heart

is that cool let's take it and look at this in a different view so now what i want you to do is i want

you to take the heart like we had over here and kind of cut it okay cut it like in a

coronal section and you're going to get this view here so if we kind of take a look here

imagine this wasn't here for a second imagine that wasn't there up here would be your primitive atria

and let's just say here's primitive ventricle here's part of that bulbous cordis again

right so if you wanted to say this here let's just say that this was part of the bulbous cordis

let's say this was the primitive ventricle and this was a primitive atria this was a primitive atria

remember what was forming between these two but it was coming like this what was it those endocardial

cushions come together and they made what septum intermedium now here's what's really cool coming off

of the septum intermedium some of these actual endocardial cells start kind of

forming these little like valves that come off of them so they form like these little valves

and then they connect the valves together you know how they connect the valves

together they make this thing called an annulus ring and then from that annulus ring comes

these little valve flaps and then guess what comes from the valve flaps guess what comes off of those

little pesky valve flaps your chordae tendini so now from that septum intermedium

what did i do i formed valves on both sides of it and a valvular annulus and little i tend

tonight i just formed the valvular apparatus but i formed a valvular apparatus on one

side particularly this is the left side guess what this is going to become get this

guess what this valvular apparatus will become this will become the mitral valve this will become the

mitral valve apparatus or sometimes referred to as the bicuspid valve guess what this one will

become the tricuspid valve oh man isn't that cool

that is so cool okay so now i form the tricuspid valve apparatus so from the septum intermedium

i formed a right av canal what is this canal here right av canal and over here i form a

left av canal and off of the septum intermedium what comes off the mitral valve on the left side

tricuspid valve on the right side and then also what forms along with those valves the valvular apparatus

which is the annular ring and the chordae tendonite let's keep going

we've now formed a right kind of inflow from the atria to the ventricles right

and we formed a valvular apparatus to provide what is the purpose of the valves to provide a one-way flow in

other words to prevent backflow from these ventricles in this case primitive ventricular bulbous cord is

back into the primitive atria that's the whole purpose now the next thing that we have to do we

formed these kind of av canals on the right and left side now let's separate the primitive atria

let's form a right atrium and left atrium now this is very i can't stress this is

so high yield if there's anything that you guys take away from this this is one of the big

ones because a lot of like diseases can develop because of

a malfunction in this process okay so from this point here here we have our primitive atria let's actually kind of

annotate this here's a primitive atria on this side primitive atria on this side and then you still know you have

bulbous cordus and primitive ventricle coming down the middle of this primitive atria

you get a little septum and this septum comes almost comes all the way down to meat

with this what is this little brown structure here in the mental middle that is our septum intermedium so you

have this kind of like tissue here that tries to grow downwards from the top of the primitive atria down towards

the septum into medium but doesn't actually reach it what is this tissue here called

this tissue is called the septum primum it's called the septum primum and because it doesn't reach all the way

down to the septumenter medium it creates a little space if you will what is that little hole there called

well guess what the name of this was septum primum you know what a name for holy ostium

so it's ostium primum so this little hole here is called the osteum

beautiful okay so in this first step of developing chambers between the atria you have a septum prima come down to

approach the septum intermedium doesn't reach it creates a space called the osteum primum

what's the next thing that happens let's come up we have again septum primum but guess what septum

primum continues to grow grow grow grow and eventually it does reach

the septum intermedium the septum intermedium was here in the center and again what color was it in this

situation it was brown so what happens here the septum prime

finally went down closed off the osteon primer but guess what

another hole develops but it develops towards the top of the septum primum what is this little

hole here called so this is still what is this structure here called this is we're going to abbreviate it septum

primum but a little hole in the septum primum develops towards the top after it completely moves all the way down

what is this little hole here called this is called the ostium

secundum crazy names so this is called the ostium secundum

all right so now we formed the ostium secondum within the septum primal what's the next thing that happens all right

let's let's get into it right sounds like i'm naming transformers right now osteum secondum and

septum prima all right let's get back into it so first thing that we have here is what

do we do we formed the all right so now let's tell you what's the m second man

from the septum primer here so we're gonna put that down right there so now we have our septum primum

with this little space there called the osteum secundum right so again right here septum primum

and then what is this little space here called this is called the ostium secundum

now another thing happens here another piece of tissue starts growing and this son of a gun starts coming down

to try to block the osteon secundum what is this one it's another transformer it's called the

septum sequundum alright so we got the septum secundum what is this one here called

this is called your septum secundum so now here's what's really important we've now

formed a septum secundum to block the ostium secundum but there's still a little space here

you see this tiny little space like right here between the septum secundum and the ostium secundum there's a name

for that little structure there this is called the foramen oh val you know why that's really

important is the baby's sitting in utero and amniotic fluid it can't really breathe

so what happens is the blood will come into this eventually the right atrium bypass the

right atrium because you know the right atrium goes to the right ventricle pulmonary circulation goes to the lungs

we don't need blood to go to the lungs when the baby's in utero that much so what we do is we bypass the blood

from the right atrium into what's called eventually going to be the left atrium

left atrium left ventricle goes to the systemic circulation which doesn't go to the heart

i mean go to the lungs okay why is this important because eventually the foraminal vowel

will close but if it doesn't it can lead to what's called a patent foraminal valley you know why that's

important is because sometimes if people develop like little clots in their legs called

dvts they can come up via the right atrium go to the left atrium

left ventricle and guess where they can go up into your brain and cause a stroke it's called a paradoxical embolus

they're not very common but again it's if this does not close alrighty so now we've developed a

septation between the primitive atria so now i can technically call this side what

the right atrium and i can now technically call this side the left atrium oh that's so cool

now let's separate our bulbous cortes and our primitive ventricle because we know primitive integral is going to

become what left ventricle bulbous quarter should become the right ventricle and then the

other part the other the superior part of the bulbous cortes becomes the outflow tracks watch this

all right so now let's erase this and again what was this little tissue here this was called your septum intermedium

at the apex of the heart at the apex you start to develop some tissue here that starts moving its way upwards

from the apex and this tissue here as it moves upwards towards the apex is given a

particular name we're trying to form another septum but this septum that we're

actually making here is called the muscular portion of the interventricular septum what is

this one here called it's called the muscular portion we're going to abbreviate this of

interventricular septum then guess what we still have a little space here

between the bulbous coordinates which become the right ventricle and the perimeter ventricle which will

become the left ventricle this space has to get filled so what happens is from the septum

intermedium some tissue moves downwards and starts to fuse with this

muscular portion of the interventricular septum what is this tissue here called this is called the membranous

portion of the interventricular septum why is that important guess what

if the membranous portion of the interventricular septum doesn't come down and meet the muscular portion of

the interventricular septum guess what you develop a little hole a ventricular septal

defect so that's another reason why this is very important

so what have we done now technically i now have this portion of the bulbous cortes

is technically now the right ventricle and now this primitive ventricle is technically now the

left ventricle now remember i don't want you guys to get confused the bulbous cordis makes two things

right ventricle and the outflow track so we still have to talk about the other portion of the bulbous cortes

but one portion of it just made our right ventricle what have we done we took a heart tube septated it to form

an interatrial septum an interventricular septum a right av canal a left av canal

what do we got to do now let's get some inflow tracks coming into that right atrium

all right so the next thing i want to do is i want to kind of develop an inflow tract

into particularly the right atrium so the next thing we have to do is take another section here remember this was

our primitive atria here this was our sinus phenosis i'm going to come

right around this level here and we're going to look at this structure here so i'm cutting it off

here you're just getting the top portion here of the primitive atria

or the bottom portion of the primitive atria and then here you're still getting a little bit of that sinus venosus

i remember what were the veins where i just want i'm not going to actually write them down i want to see

if you guys remember them coming into the sinus gnosis we have the inflow tracts

from the outsides what were these your common cardinal veins here what were these umbilical veins

here what were these vital and veins the the common cardinals the umbilical and the vitelline veins

empty into their horns this was the left horn and this is the right horn

all right so what i need you guys to understand is again we have the left horn right horn

feeding into the sinus venosus which will feed into the primitive atria okay now remember

left horn right horn are fed by three vessels right we had again what were these common cardinal veins on

the outside and the middle is your umbilical and on the most inner part are your vitalin veins

what happens is all of the veins on the left horn break down all that's left over is just the left

horn so now i just have the left horn okay then on the right horn we're just going to abbreviate this

r h what happens is the um umbilical vein actually starts to degenerate and all that's left over

feeding into the right horn will abbreviate this is the common cardinal vein and the

vitalin vein so all that's feeding into the right horn is the common cardinal vein and the vitelline

vein and all the tributaries off of the left horn break down the next thing is not only do

those actual tributaries break down but the left horn starts kind of shifting towards the right

and actually kind of fuses with the right horn a little bit before it enters into the

sinus phenosis so again here we had above this where these horns enter in your sinus

vinosus and then above this would be the primitive atria now here's what i want you guys to remember

when this is actually fusing right whenever these structures are all kind of like

changing and going through their kind of digression and specializing this sinus phonosis gets

absorbed into the primitive atria so the sinus venosus will get absorbed into the

primitive atria so whenever the sinus venous gets absorbed into the primitive atria the

left horn is going to develop a very special structure guess what this little

little structure is this is called your coronary sinus so the coronary sinus is formed

from what from the left horn then again whenever the sinus vinosus

gets absorbed into the primitive atria the common cardinal vein is going to be up here towards the top

this common cardinal vein will be what's called the superior

vena cava the superior vena cava is formed from the right common

cardinal vein and then this bottom part here remember how the actual from the right horn you

had the vitelline vein whenever the sinus venous is absorbed into the primitive atria

this right here is the inferior vena cava and the inferior vena cava is formed

from the vitalin vein which one particularly the right

vitality okay so that's what i wanted you to understand so the inflow tracks coming into the atria

because of the left horn shifting towards the right and all of its tributaries breaking down

and kind of feeding into the right horn a little bit before it enters into the sinus phonosis

whenever that gets absorbed into the primitive atria it gets absorbed into the right side of the primitive atria

and again coronary sinus is formed by the left horn the supreme vindicator is formed from

the right common cardinal vein and then the inferior vena cava is formed from the right vitalin vein

beautiful and then these are taking blood and emptying them into

the right atrium isn't that cool so now not only formed left atrium right atrium right ventricle

left ventricle right av canal left av canal we also have the inflow tracks coming into the

right atrium isn't that cool now we got to come to the annoying part

now we finally have to go over the bulbous cordus and the truncus arteriosus

and how they make those outflow tracks let's do that now all right so we're looking at another

kind of again kind of a coronal section of the heart and again so you can kind of have an

idea here we've already formed our right atrium we've already formed our left atrium

we have let's say that we we haven't covered let's just kind of rewind a little bit and say at this

point we haven't formed the membranous part of the interventricular septum but for the most

part we have our right ventricle we have our left ventricle here and here you can see

like these little canals you see those little canals those little holes there that's your right av canal and that's

your left av canal okay now remember we said that the this portion of the right ventricle is made

by the bulbous cortis right but we also said up here we have another portion of the

bulbous cortes and up here we have a portion of the truncus arteriosus

okay what i want us to do is i want us to take a cut from here and here

and really kind of look and see what is actually happening that we form a defined aorta

and a defined pulmonary trunk and then on top of that the valves that are going to be allowing for a one-way flow

from the right ventricular outflow tract and left ventricular outflow tract into their respective pulmonary trunk

and aorta okay so if we take a section here and here we get this kind of structure here

so again at the top top portion here is going to be your truncus arteriosus and towards this bottom portion here is

going to be the bulbous cordis okay all right beautiful now what

happens is you start to form little again neural crest cells what are they for what are they called again

neural crest cells start to infiltrate into these areas here so some of these neural crest cells

are important for forming what's called the aortic pulmonary septum but some of these neural crest cells

they kind of migrate into this area here okay when they migrate into this area they

start forming little like endocardial ridges or kind of

cushions kind of coming outwards at the truncus arteriosus is the top part you get a truncal ridge that forms like

this okay and then another truncal ridge that forms like this okay

at the bottom part of the bulbus cordis you get a bull bar ridge that kind of comes in like this

and again you get another bull bar ridge that comes in like this okay now there's another

ridge in here that has actually formed but it's not in a view that we can see this is forming like on a left side and

a right side kind of coming towards each other there's another one

in the middle you can't see the way it's forming but it's forming from like an anterior

posterior view so what i'm going to do here is i'm just going to kind of draw it like this

so you have a ridge coming from the anterior portion and you have a ridge coming from the posterior portion and

they're trying to approach one another whenever these ridges kind of approach one another and come

together they do this kind of like spiraling around the central axis all right so now

what i want you to remember is that those truncal ridges right they come together and whenever

those truncal ridges come together at the top part right where the truncus arteriosus is

they kind of form this like little septum that separates this kind of whole what is going to become

the aorta and the pulmonary trunk into two sections which will again give us one portion of that little

septum will flow into the pulmonary trunk one of that section will fall into the

aortic arch but again what happens here at this level of the truncus arteriosus here

okay this is going to be forming what's called truncal ridges and again what happens is the truncal

ridges come together fuse and then kind of form a nice little septum here

same thing at the bottom right here at that bottom portion here where the bulbous

cordis is again you get those bull bar ridges coming from both of these edges

and they meet in the middle and form a nice little septum okay so again you have those nice bull

bar ridges they come together and they make a little septum

and then we said here in the center still part of the bulbous cord is technically another area we call the

conus cordis we're not going to get too much into that but they form anterior to posterior so

we're just going to kind of draw a central line there what i want you to now do is that

because the way the coconus cordis ridges form and lead to a septum it

causes this entire septum that runs down the link of the top from the trunk of arteriosus to the