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so we're going to be talking about the
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embryology of the heart and we're going
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to break it down very simply so that you
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understand everything that's going on
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I've drawn a lot of crap up here uh
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don't let it confuse you don't even look
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at it yet we'll go through it step by
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step and you should be by the end of it
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understand what's going on okay so let's
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just begin at the beginning the first
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thing that happens is the egg is
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fertilized it moves down the uterine
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tubes and you'll get something looking
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like this that's called the blastula
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that's what you were before you were
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born before anything of anything
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happened so as the blastula migrates
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down into the uterus it implants into
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the uterine wall and a process of
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gastrulation will form the three germ
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layers and I'm sure that you've seen
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this everywhere it's a simplification of
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what we see here so we have that there
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the top layer in blue that's the
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ectoderm the ectoderm gives to the
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epidermis and the central nervous system
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in the middle we have the intermediate
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mesoderm and at the bottom in green we
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have the
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endoderm so the intermediate mesoderm
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has three main components to it first it
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has the paraxial
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mesoderm the paraxial mesoderm gives
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rise to the somites so you'll have your
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muscles coming developing from the
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paraxial mesoderm you'll have the
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intermediate mesoderm
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and the intermediate mesoderm gives rise
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to the gonads and the kidneys and
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finally we have the lateral plates at
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the end so the lateral plates are made
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up of two uh different plates we have
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the
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sematic and we have the
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slanking now the heart is derived from
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the splank niic lateral plat so the
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splank niic mesoderm so
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the main thing the first thing that you
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should know is that the heart where is
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it derived from from the mesoderm from
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the lateral plates from the spanic
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mesoderm so the progenitor heart cells
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they actually migrate from the
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epiderm I mean oh sorry for the from the
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from the ectoderm cells from the
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ectoderm and they migrate down the
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Primitive
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streak into the spanic mesor so as they
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are migrating they'll live and where the
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spanic mesoderm
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is and this section now will be called
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the primary heart field now the primary
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heart field gives rise to the uh left
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ventricle the Atria and part of the
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right
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ventricle so um where does the rest of
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the right ventricle come from it comes
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from a section called the secondary
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heart field now if we have a just give
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give me your attention just to this over
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here don't don't look at anything else
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just look at he and it might be a bit
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difficult to understand but we'll get go
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through it so what happens is the rest
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of the right ventricle comes from here
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so you have this section here where the
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secondary heart field is and in red here
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we have the the heart so we have the
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primary heart field made from the
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cardiac myoblast and the blood Islands
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from that were from the spanic mesoderm
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making up the heart over here which
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we'll go through in a second and the
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rest of the heart is derived from the
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secondary heart field over here which is
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still from the spanic mesome so this
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here is still from this section over
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here okay so what happens is it sends
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cells down and it builds and elongates
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the
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U the the heart and it is responsible
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for building up the truncus AR
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arteriosis and the conus Cordis so
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that's just and and it's important to
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know this because any shortages any
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defects in the secondary heart field
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would lead to defects in child birth so
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um with that being said let's move on to
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how the heart is actually developed
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so this Pokemon looking uh creature over
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here is a uh day 18 cross-section of of
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the embryo so it's got this big green
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tongue that's still the
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endo and and as it folds if just just
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pay attention to the green the Green's
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the Endo has nothing to do with the
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heart but just to get an idea of what's
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going on it'll form the Primitive tube
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over here primitive gut tube so this
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green endoderm Pokemon tongue becomes
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Pokemon mouth into the Primitive uh gut
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tube right over here so
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let's pay attention to the Pokémon's
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face now so its cheeks and its eyes the
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whole Pokemon over here in red is still
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the spannick mesoderm it's still this
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bottom section of lateral plate so what
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happens is as it folds the blood islands
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and the cardiac myoblasts will form
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these endothelial heart tubes
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and this dorsal
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aot and to get an idea on what that is
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how that actually looks like because
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this is probably still looks like a
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Pokémon to you you don't know how the
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heart is derived from that just let's
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flip this like this just like and then
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you'll have something like this over
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here so you have your endo tubes here
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and I'm sure you've been exposed to that
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before you've seen what that is so you
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have your venous blood coming in and
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going up and what happens as it fall as
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the embryo Falls both dorsally and
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cranially it also falls laterally and
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that will
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cause the endothelial tubes to join so
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these are the endothelial tubes this is
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a a flipped up
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version and so what happens is that
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fuses into one over here on day
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22 and likewise the dorsal aot they will
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fuse and become the descending aorta so
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the cheeks of the Pokemon they're the
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endothelial tubes don't let it don't get
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too confused about
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it it's just this so this is this and
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that is that so blood flow is coming up
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and that would be eventually the
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descending aort over here
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so coming looking at this uh Pokémon
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that has transformed into whatever it is
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now with the mouth you have over here
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the single cardiac tube the heart tube
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which can be which is equivalent to this
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or this so if we flip this up again
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you'll see either this or this so um and
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these obviously are the dorsal aor which
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will eventually fuse together and these
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are this is no longer an endothelial
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tube you can say that it's the heart now
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so the heart has begun
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pumping and so on day 22 so we should
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probably go through this each the the
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anatomy of of each section so the bottom
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over here we'll have the um we'll have
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the
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atrium and we will also um
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the sinus
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venosum so the sinus venosum gives rise
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to the Smooth Wall layer of the atrium
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The Atrium gives rise to the left and
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right atrium and this B big bul section
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that is The
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ventricle and that gives rise to the
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left ventricle and then we'll have
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the bulus
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cordus um
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and also the truncus
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arteriosis so if we have we still have
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the atrium here maybe in this section
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The ventricle here the Volus Cordis and
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the truncus A arteriosis and essentially
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how the heart folds is that the bous
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Cordis and the truncus arteriosis they
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fold ventrally and
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dorsally and The ventricle Atrium and
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the sinus venosum squished up behind it
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so you'll have this if we look at it
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from a little bit of a side view a
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squishing up happening if I can explain
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it in that simple way so the truncus
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arteriosis and the bulbous Cordis move
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uh fold ventrally and dorsally so
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forward and down and squish up the rest
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of them so and by day 24 we'll have the
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heart looking like this and at day 28 if
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we get the frontal section it'll look
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like so you have blood flow leaving the
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heart from here and receiving it from
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the back so this over here is behind
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this heart right now so on day 30 if we
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just slice the heart like this on day 30
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we'll have a heart looking like
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something like this and I'm just going
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to I'm not going to go into too much
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detail I'm just going to discuss the
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blood flow in it and essentially the
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um how it develops so we'll have veinous
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the blood FL coming
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in like this so it comes in here from
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the atrio ventricular section and flows
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in from the to the
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um uh out through the truncus arteriosis
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here So eventually as the heart develops
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the septum
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will form and this uh will go into two
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parts like this
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okay that's out of
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the we'll discuss that the development
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of each septum in a different video but
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essentially what happens is um right
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before birth the heart will look like
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this but not really I'm going to go
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through the development of the foran oal
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as
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well to finish it off
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so what happens is
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we have a bud growing from the top of
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the heart called the septum
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primer and also from this endothelial
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cushion we have a bud growing and
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eventually they
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grow in a way so that they meet each
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other and form completely but before
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they form completely cell death causes
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the top part to uh open up like this
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and at the same time we'll have a septum
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second
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growing from the top and from the
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bottom so the Gap that the septum second
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leaves so that's the septum
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second and this is the septum Prim
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so the Gap that the septum second septum
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second leaves that's the that's the
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foran foran oal so just here this
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section is the foran oal and it's very
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important to understand this because um
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defects in this uh can contribute to uh
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tetrology of the heart such as the Tet
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tetrology
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of for example that's the
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uh disruption in the foral is one
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component of that so what happens is
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before birth the pressure in the right
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atrium is much higher than the pressure
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in the left atrium so what that causes
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is blood flow to
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to be pushed from
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here into here so this septum primum can
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act like a valve uh and the purpose of
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that is to bypass the pulm
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circulation so at at Birth however what
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you'll have
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is a pressure change where there's
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increased pressure in the left atrium so
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what that causes is the closure of this
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valve and eventually in with uh
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increasing pressure in here more than
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more so than here the prim the septum
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primum and the septum second will fused
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and permanently shut so that's how the
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foran oil is closed and that's a general
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overview of how the heart is uh
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developed if you have any questions
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please leave a comment under the video
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thanks
