Embryology | Gastrulation

0:00 I engineers so we're going to continue talking about the development of the embryo we already finished if you guys haven't already seen it go watch our first video which is the development up until week one right so we talked about fertilization we talked about cleavage and we talked about the formation of the blastocyst right and then how we got to the end of that we're going to now go into the development throughout the embryo up until week - and we're gonna mainly talk about in this video gastrulation will have a tiny little peek into implantation but i don't want to get into too much detail on that reason wise we'll go more into that when we talk about the development of the placenta okay but let's see where we left off we left off talking about how the trophoblast right which is the outer cell mass used to be the outer cell mass we said it's gonna get derived into a saito trophoblast in a syncytium oblast and we'll talk about their significance

0:58 we also talked about how the inner cell mass it differentiated become more specialized and it became the embryo blast and how it starts to differentiate and become a little bit more specialized and it forms what's called the by laminar disk right it's gonna become the embryo trophoblast is important because it becomes a part of the chorion and it becomes a part of the placenta which is very important for being able to provide oxygen nutrients get rid of waste all right between the mother and the fetus so we finished off here with our kind of like the in part here where we had our trophoblast with which is we said are gonna differentiate these two in the embryo blast remember what did I say embryo blast turns into a biomatter disc we're gonna talk about this a little bit more in just a second I want to focus on the outer layer now that's where I can get a little bit tough is when you focus on these things you want to focus on one

1:47 part of the time what I want to do first is we're gonna talk about that outer layer first just a little bit again we'll get into a more and when we talk about the development of a placenta but I want to talk about what the significance of the trophoblast is then after that we'll come back and we'll talk about how the embryo blast develops into the Tri laminar disk via the process of gastrulation alright so what I want to do is let's go back into our diagram and talk about what's happening from this okay all right so let's go ahead and take a look at our diagram again so here we have the uterus right and we already talked about what had happened to this point we already said about how the anti pituitary releases the LH right LH triggers the ovulation process where we pop out that secondary oocytes all right and it's frozen in metaphase to in the ampulla then we said that the sperm is going to meet the actual Oh a site frozen a metaphase to at the level the

2:39 ampulla we're going to get fertilization and then that whole process of cleavage is occurring right and we talked about how cleavage is basically going from the zygote to the four cell stage at the eight cell stage to the sixteen stela stage and then to the blastocyst well what happens is when all of this cleavage process is occurring this actual zygote or these different cleavage process are actually they're moving towards the uterine cavity so then what happens is that little blastocyst it kind of just pops off here into the actual uterine cavity and then what happens is it has specific types of proteins on it certain types of selectins or integrants that allow for it to hook up with the endometrium and start implanting itself right so what we're gonna do now is we're gonna take a deeper look looking at how that actual that blastocyst is going to implant and what are the processes with that outer trophoblastic layer okay so what we have

3:36 over here again don't worry yet about the by lemon or disk we'll talk about this a little bit later but remember we said that there's an outer cell layer this outer blue lining we're called that the saito trophoblast well the trophoblast which divides into a side of trophoblast and since seetio trophoblast what happens is imagine here for a second you have these well-defined cells okay and here they are these kind of like baby blue cells right there we're gonna have these well-defined cell margins these are called your Saito trophoblast so you have the well-defined cell margins with the nucleus inside of the cell right what happens is some of the other cells start proliferating and as they start proliferating their cell membranes actually start disintegrating so they start proliferating outside of that zone Lucido right remember how we had this zona pellucida enzymes that allows for it to kind of break outside of that and as it does that these cells start

4:37 proliferating outside of the cell and then their cell membranes start disintegrating when they start disintegrating it forms kind of a fluid if you will kind of a cytoplasm which is going to be consisting of the nuclei of these cells right so what happens is all the cell membranes of these cells start actually breaking open and releasing out the nuclei and the cytoplasm into kind of just a little area and what happens is all of the cytoplasm starts kind of fusing with one another forming a syncytium right and that's going to be our sense Ischia trophoblast so this part here which is going to be kind of like these finger-like processes that are kind of extending out into the uterus so this is our uterine lining right here this is going to be called D since isseo TRO fo the last okay and again it's important to remember just why I give you guys a good idea here imagine what theirs are the cells right here's the finger process all of the actual nuclei

5:44 are just kind of sitting out here in the cytoplasm there's no well-defined cell margins okay that's our sensation your trophoblast at the base you're gonna have these well-defined cells which have their cell membrane and the nucleus with inside of that eventually what will start happening is that these cells will start actually forming kind of a defined cell kind of like finger process or a villi that extends through the center of this up into the center of that actual Vil's right but again for right now I want you to remember all this cytoplasm on the side with the nuclei kind of just within that fluid is called this in Ciccio trophoblast and then the cells with the well-defined Mar margins or membranes with the nuclei inside of them are called the Saito trophoblast so again these are your Saito trophoblast and again the syncytial Truffaut blast is going to be just the actual syncytium of all the cell cytoplasm and nuclei kind of just sitting in this kind of

6:47 pool of fluid all right why is that important well eventually what happens is the sense issue a TRO full blast will continue to kind of release certain types of hydrolytic enzymes that'll work its way through the actual uterine lining and guess what out is out here in the uterine lining you have these maternal blood vessels so let's just say here's gonna be like a maternal blood vessel here's gonna be a maternal blood vessel and here's another maternal blood vessel what's eventually going to happen is that this actual sense issue trophoblast is going to continue to keep working its way out here to kind of become confluent with these maternal blood vessels because once this actually becomes complement with the maternal blood vessels now the actual embryo can receive oxygen nutrients hormones everything it needs in order for it to grow because there's going to be a connection between the embryo and the maternal vascular system via that since

7:43 this yo trophoblast and saito trophoblast so that should make sense once it implants right via the integrants and selectins to the uterine lining it's gonna burrow itself in a little bit and then what happens is those saito trophoblastic cells are gonna start proliferating and working its way through the zona pellucida making these finger kind of like processes the cells with inside of those finger-like processes start to disintegrate and break down their cytoplasm spills out of them and their nuclei spills out of them and they form a pool of what we call a syncytium right which is going to be this syncytial trophoblast then eventually what happens is the saito trophoblast continues to proliferate these cells and they proliferate right into the center of that actual villus and eventually what's going to happen is this actual structure is going to become confluent with the actual maternal blood vessels and before you know we're gonna have a placenta a

8:37 connection between the vascular system of the the mother and then the embryo all right and that's going to be the development of the placenta we'll talk about that more detail later I just wanted to give you guys a little look into this now a little bit later throughout the process we're gonna kind of jump a little bit forward as this actual embryo continues and continues to develop right here's the important thing we remember we said that the corpus luteum ejected out the secondary oocyte and LH right now is much driving the production of progesterone right and we're up to about we said that it happened around a 14 day 15 we've already gone through about a week all right so we've already done about seven to eight days by now for the point of implantation as we start getting closer to day 28 what starts happening you start shedding the endometrial lining how do we prevent the endometrial lining from getting shed well guess what happens a little bit later towards the

9:30 you know Ronde 24 maybe day 21 to 20 to 24 that's in Ciccio trophoblast it starts actually making a specific type of hormone so cool it starts releasing what's called beta h c g okay which is human chorionic gonadotropin now remember I told you that progesterone levels start to drop later on in the luteal phase when that sensation at rofl blast releases the beta HCG guess what it does to the corpus luteum of the ovary it has it continued to produce what progesterone and so the progesterone is going to remain elevated the reason why that's important is once the progesterone levels start dropping what happens to the vessels with inside of the uterine lining they start spasming and as they start spasming what happens they rupture and then as they ruptured the cells inside that endometrial lining start doing what they start actually becoming necrotic and they start getting shed and if we shed the endometrial lining what else when we shed the embryo and and we want this to

10:35 happen we want them to be able to allow for the implantation we don't want this to get shed out so if it releases paid HCG it triggers the corpus luteum to continue to keep making progesterone if progesterone levels maintain a certain level we're not going to prevent those vessels from spasming and so we're not going to allow for shedding we're gonna allow for proper nutrition glycogen all the different types of lipids to be produced to nourish the baby and so there's not going to be any shedding of the in Dimitra to ensure that there's proper implantation so that's such a cool thing again go into more detail about implantation the development of the placenta later let's come back here and talk a little bit more about how the development of the embryo is occurring all right so now we talked already about the process of the implantation just wanted you guys to not be like wait we're at what happens to the trophoblast because we're primarily gonna be

11:23 focusing on the embryo blask and the whole process of the bilaminar disk converting into the trilemma inner disk so again a little bit of information on that we'll go into more detail later what what we're gonna do now is just so we don't have to focus on that trophoblast we're just going to take out that bilaminar disk okay in the cavity above it and the cavity below it and just see what happens specifically with that okay so take that out now and here's the structure that we get let's make ourselves kind of understand what's going on here with this structure so bilaminar two disks right - two sheet-like disks the top layer is an important layer okay the top layers will be called the EPI blast okay so the top layer is the EPI blast the bottom layer is actually going to be what's called the hypo blast and again this is actually going to be a part of the bilaminar disk so this is the two components of the bilaminar disk now below the bilaminar disk is going to be

12:23 a little cavity and what is that cavity called that cavity is going to be called the yolk sac so it's kind of like the primitive yolk sac so we'll put here Y s this is just going to be the primitive yolk sac okay above it is going to be a fluid filled cavity and this is going to be called the amniotic cavity so just so you guys have a little bit of an idea of what this actual microscopic structure is is again epi blast hypoblast two layers sandwiched together above the EPI blast is the amniotic cavity and below the hypo blast is the primitive yolk sac okay eventually this will help with red blood cell production in the actual embryo okay but it provides a lot of nutrients as well now what I want us to do is and I want us to look at this in a way that helps us to kind of see what's going on because that's kind of the big thing with embryology is seeing the process seeing the way that cells are moving or the way things are migrating

13:20 it's the toughest part all right so what I want to do is is I want to take a look at this actual by lemon or disk imagine we're looking at it from the top okay so we're not going to see the EPI the hypo blast we're only gonna see the EPI blast from the top okay so imagine it's kind of like this okay so we're looking at it from the top now what I have here is on the top you're gonna have this little kind of like little fused area it looks kind of like I think it'll thickening or kind of like a depression maybe you'll see it it's called the pro portal plate and this is good because the reason why is this gives us kind of our orientation of anatomy so here we're gonna call this the pro chordal plate and what the pro chordal plate is is where the EPI blasts and the hypoblast are kind of just sandwiched together okay but the pro chordal plate gives us orientation of cranial and caudal so with respect to the actual pro portal plate the top part

14:16 of it near it is going to be the cranial end okay or the head end away from it down towards this side is going to be the caudal or the tail portion okay so here we're gonna have that and then here we're gonna have this there's actually another membrane down here if you really want to know you'll have another membrane at the bottom here called the cloaca membrane and then you'll have a membrane right in front of the pro quarter plate which is called the bucko for ngo membrane why that's important is buckle fur and geomembrane guess what that makes the mouth guess what the cloaca plate makes the butt hole okay so I'll show you the two ends okay Pro quartel plate though it gives you a kind of an idea specifically of your positioning so again cranial end is where the pro chordal plate is caudal end is going to be down here where the cloaca plate is and then you'll have a membrane right in front of the actual pro chordal plate which is called the

15:17 buccal four-engine membrane what I want us to do though is is we're going to make a section okay I'm gonna make a section and we're going to look at it right here so I'm gonna cut right here imagine I'm taking this piece I'm looking at it from the top I'm now going to take this section and look at it and kind of like a more of a coronal section so we're gonna look at it more of a coronal section so now this is the one we're gonna focus on and now you're going to be able to see the hypo blast and then epi blast and then this little black area here is going to be the pro quartel plate here's what starts happening at this stage right so we're getting ready that we're trying to move from week 2 all the way up to week 3 what starts happening is there's some signaling processes that occur and these signaling processes start causing the EPI blasts cells to form kind of a thick area on top of them so you're gonna get like this very thickened area of epi

16:18 blast cells and it's gonna make what we call a primitive streak ok so here you're gonna have the primitive streak which is gonna be this part okay and towards the actual cranial end you're gonna have like a little knobby and that little knobby is going to be what's called the primitive node so you have the primitive streak which is kind of a thickening of the epi blast cells and the primitive node which is kind of like this knob like structure towards the top of the primitive streak now here's where it gets really cool eventually what happens is some of the cells in the center of the primitive streak start dying in some of the cells in the center of the primitive node start dying and what's cool about this is now it makes like this little structure that we're gonna have over here on the right I just wanted to give you guys kind of like what's happening with this so we had the primitive streak which is a thickening

17:20 of tissue primitive know which is a knob like thickening of tissue and then what happens is some of the cells within the center of that shrieking notes start actually dying and making a little cavity pretty cool right now why is that cavity important okay come over here some of the cells near the edge of this primitive streak right start secreting certain types of chemicals right what kind of chemicals did they start secreting they start secreting chemicals which are called fibroblast growth factor 8 there's other types too may be transforming growth factor beta but this is the main thing that the actual cells here near the edge are going to start secreting so they're gonna start secreting these chemicals these fibroblast growth factor 8 now what is this fibroblast growth factor 8 do it's so it's so freaking cool what it does let me show you these cells they start secreting that fibroblast growth factor 8 that fibroblast growth factor 8

18:24 is going to move these nearby remember I start secreting it laterally so it's going to move from the center moving laterally and it's going to go to these nearby epi blast cells when it binds on to the EPI blast cells it has a receptor so it's a fibroblast growth factor receptor once it binds on to this receptor it triggers an intracellular process right and this intracellular process what it does is it activates a specific type of protein called snail one heck of a name right so a fibroblast growth factor binds on to the receptor triggers an interest rate of the process that stimulates the formation of a protein called snail one now what snail one does is it inhibits the formation of a specific type of protein that allows for cells to be linked up with one another do you know what that protein is called it's called eek adherence so it's called E can't hear ins now what ECAD hearings do is they allow for cells to stick with one another so here's another epi blast

19:34 cell so two epi blast cells connected to one another through this ich adherence now with these ECAD hearings the cells aren't allowed for to move away from one another right so they're stuck to one another they're in a localized place if you stimulate this protein with the fibroblast growth factor guess what it does and inhibits the formation of these proteins if these proteins aren't connecting the two cells with one another what can they now do they can migrate so now this cell is free to move and this cell is free to move guess what they call that epithelial migration okay so it's called epithelial migration so now these cells that are going to be over here on the lateral side guess what they're going to start doing they are going to be stimulated and they're gonna start migrating towards that primitive streak now here's what's so darn cool once they move through that primitive streak right remember there's a little space there we had the primitive streak which of the

20:38 thickening in the primitive streak that little space that we have there now we actually call it the primitive groove if you really want to be particular the primitive streak was the thickening with no space now that it has the space that's called the primitive groove what we used to have Lister was the primitive node which is that knob like thickening and it has a space now is technically called the primitive pit I'll write that down just for the heck of it though right so what used to be the primitive streak is now going to be called the primitive groove which is going to be again that space right there and then what used to be the primitive node is now going to be called the primitive pit and all it is it's just basically saying this space within the primitive node and the space within the primitive streak that's all it is so we released the fibroblast growth factor 8 those epi blast cells are now going to be free to move where are they going to move

21:31 they're going to move through the primitive groove once they move through the primitive groove guess what happens now look at this let's make like a little space here too so we can see how these little are moving so now what they're gonna do is they're gonna move through this primitive straw groove right when they move through the primitive groove they're gonna move down here where the hypoblast is but guess what happens remember this was the hypo blast right these cells the EPI blast cells that are now going to be functional and able to move they're going to move down and they're going to replace the EPI blast so again I can't stress that enough the EPI blast cells that are moving through the primitive groove now down through that and into where the hypo blast used to be it's going to be replaced with these epi blast cells so this will no longer be what we call the hypo blast we're actually gonna call it B endoderm

22:30 okay it's gonna become the endoderm now what happens is again the EPI blast cells will continue to release more fiber Blasco factor 8 and cause more of these epi blast cells to continue to keep moving towards that primitive groove but then remember more growth factors released causing more epi blast cells after the endoderm has been formed remember that after the endoderm has been formed more epi blast cells are being stimulated to move through that primitive groove and down where do those cells go and how do they move is important because they're going to form the music room so let's come up here for a second alright so we've already had the cells which are all here in orange we've already had these cells replace the actual what we've already had these cells move down and replace the hypo blast and form the endoderm and we're gonna see that in another diagram in a second remember I told you more growth factor is released when more growth factors release more of these heavy

23:35 blast cells start moving through that primitive streak but guess how they how they do it this is the cool part they move through this actual primitive primitive groove and when they do that I'm going to show this in kind of like a broken arrow here they move through and they move so you had here these cells coming in right and then when they come in they move to the side and forward coming in to the side and forward coming in to the side and forward and they're gonna keep doing that now as they start filling up that area first layer we had we replaced it right we had the hypo blast what did it become now I told you it becomes the endoderm I wanted to turn it into a different color so it was this green now we're gonna have it as a dark green so again epi blast cells migrated through first they become the actual endoderm so now this layer they used to be the hypo blast is now going to be called the endoderm all right that's going to be

24:40 represented by these orange it's orange arrow the cells move down through the primitive groove move in replace the actual hypo blast cells some books will say that they replace all of it some will actually say that there is still some hypoblast cells that are actually remaining within that endodermal layer okay then we said after the hypo blast is replaced and turned into the endoderm then we said more epi blast cells are going to move through the actual primitive groove down out and forward and they are going to make the new layer which is going to be this red layer that red layer that we have there is going to be the mesoderm and then what do we have left up on the top that didn't change right it should still be the ectoderm or actually we're gonna that's what we're gonna call it now so now instead of it being the EPI blast we now call a P ectoderm all right so let's recap just because this is one of the tougher parts okay first layer you have is epi blast

25:45 bottom layer hypo blast right you have the primitive streak now remember the primitive streak was the thickening of the EPI blast tissue here and then you're gonna have a primitive node which is the thickening of the a P blast tissue kind of Annanagar form the tissue in the center of the primitive streak starts to disintegrate and form the primitive groove the tissue inside of the center of the primitive node starts to disintegrate inform the primitive pit then the EPI blast cells right around the edge of this primitive streak in the primitive nodes start secreting a chemical called fibroblast growth factor type 8 there's also other ones like transforming growth factor beta as well these chemicals what do they do they cause the epithelial cells are these epi blast cells to no longer become adherent to one another by inhibiting the formation of ICH adherence which of these cell to cell adhesion molecules if those aren't linked up now these epithelial cells can

26:41 migrate or the EPI blast cells can migrate now as they start migrating where do they move remember they move first through the actual primitive groove downwards and then what do they do first they've replaced the hypo blast so this was the hypo blast what does it become next it becomes the endoderm and then the EPI blast is what we call the ectoderm now the ectoderm is still going to release fibroblast growth factor alright so more fibroblast growth factor is gonna be released causing more of these epi blasts or ectodermal cells to continue to migrate towards the actual primitive groove but now in this maroon or purplish color these ones when they move through the primitive groove they move down laterally and forward okay as they move down laterally and forward they make a new layer which is called the mesoderm okay so this is gonna form our three germ layers now this process is super critical because this where we go from a by laminar disk to a trilemma Nordisk

27:50 it's a specific type of thing and we call that gastrulation so that's the importance that we have to understand this process here is called gastrulation now the next thing that has to happen is now that we have our three layers here's the next part that gets really cool what happens is again more growth factors going to be released this growth factor is going off the hook alright and it's causing more of these ectodermal cells to continue to keep migrating through but now instead of migrating through this actual primitive groove they only migrate through the primitive pit and as they start migrating they move through the primitive pit and they move cranially towards the pro quartel plate but when they move you know it's so crazy they form like a tube so they're gonna move through the actual primitive pit and and they're gonna move cranially or we can say cephalic towards the pro chordal plate and they're gonna make this tube now I want us to see this

28:58 tube from a different two different ways once they move through they're gonna make a tube so imagine here this is going to be the ectoderm this red here is going to be the mesoderm and this dark green here is going to be the endoderm here you're gonna have this whole inside of the ectoderm what does that hole called that is the primitive pit where the primitive node is what happens is those ectodermal cells are going to migrate and move their way through the actual primitive pit and they're gonna make this nice little elongated tube that moves underneath the ectoderm but above the endoderm but as you can see here where the nodal cord is there is no mesoderm there's three places that you have to remember that there is no mesoderm between the acto Derman the editor one is where the notochord is second is get what do we call this place right here where the front end or the cranial end where we kind of define cranial and caudal we call that the pro chordal

29:58 plate right so if I were to put right here I'll black kind of lines here connecting this right here is called our pro chordal plate right and we said right in front of that is where you're gonna get your buckle for enjo membrane right where the oral cap forms right back here what do you think he's here the cloaca plate right so back here you're gonna have the cloaca plate or membrane we'll call it the plate and that's gonna form the butthole right now three places where there's no meezerman one is where the notochord is second is where the pro quarter plate is three is where the cloaca plate or the colloidal membrane is now I wanted us to get that view so how we're looking at this just so you guys kind of get an idea is all I did was is I'm taking this piece here this coronal section that we're looking at here and which is on a three dimensional structure and I'm making a sagittal cut so imagine I'm cutting right down the middle here of this primitive streak kind of making a

31:02 bilateral structure okay so I'm getting a sagittal cut here and this is how we're looking at it all right so again that's gonna be the nodal cord so that's an important thing to remember the cells that are moving through the primitive pit moving cranially totes the towards the pro portal plate which is making a nice little tube or tubular process is called the nodal cord why is the notochord important because the nodal cord is what helps to induce neural ation which is another topic that we have to cover so what is this structure you're called this is called the no toe cord and if you guys are real good you guys will remember that what happens to the nodal cord after you've actually been developed so what is it in the adult what is it the remnant of it all right so imagine here we have the notochord what happens is you have an intervertebral disc right and so here's the disc right and the disc is actually going to be made up primarily of dense fibrous kind of irregular connective

31:57 tissue okay we call this two annulus fibrosus right but if I were to kind of make this into a three dimensional structure let's say okay in the center of it in the center of this disc is a kind of a jelly-like material and this jelly-like material is called the nucleus pulsus so right here in the center I'm gonna have this jelly-like material which is called the nucleus pulposus nucleus pulposus that is the adult remnant of the notochord so again notochord forms right and it's going to be important because it releases certain types of growth factors that causes the thickening of the ectoderm which forms the neural plate which allows for neural ation but on top of that as they start to develop right you're gonna have the remnants of it which is gonna be the nucleus propulsions which is the little jelly material in the annulus fibrosus of the intervertebral discs which is between your vertebrae alright so that's the important thing so again this is just

33:01 going to be a sagittal view so just so you understand this is gonna be a sagittal view of that previous diagram and then the one below it is going to be the same diagram but just showing you now what it looks like to have the actual notochord so imagine again what happens is that the actual ectodermal cells move through that actual primitive pit and move and make that tube well now here look here's your ectoderm here's your Mesa derm and here's your endoderm and what do you call this little tube here which is just actually in between the mesoderm that's gonna be the notochord and that's important to remember now later on what happens is the Me's a derm it'll actually differentiate right it'll become into three different components it'll become the PAR axial which is the central part then the intermediate musiim which is important for making like the kidneys and the gonads and then towards the edge you'll have the lateral plate mesoderm and that's going to differentiate into

33:59 what's called splanchnic which is gonna surround your GI organs it's the muscle around the GI organs and some of the connective tissue and also you're gonna have this somatic which is going to be basically forming around a lot of the body okay forming a lot of the body structures so that's important to remember as we'll see in another video the ectoderm is going to be able to make the skin and a lot of the nervous system and the endodermal is gonna be making the lining of the GI tract it's gonna be making some of the accessory organs that glands and we'll talk about that as well but again important to remember the whole purpose of this video here is to get what happens with the outer cell mass which is basically the site of trophoblast and the since this your offal bless what is there significance implantation right and formation of the placenta we'll go into more detail into that in another video what was the other function of this

34:49 video the other purpose was for us to understand what happens with the inner cell mass which is the embryo blast which is gonna be making what bilaminar disk by eleven or disk is important if we blow it up we'll see what happens thickening of the EPI blasts is gonna give us a primitive streak and note that some of the cells will then break down give us the primitive groove in the primitive pit it'll release growth factors the growth factors will cause the EPI blast cells to move through the primitive groove below it into the hypo blast replacing the hypo blast and turning it into endoderm more growth factor will cause more epi blast cells but now what we specifically call ectodermal cells to move through the primitive groove and primitive pit and then make a new layer called the mesoderm then after we have the three layers or our trilemma Nordisk through the process of gastrulation we then lead to the formation of the notochord which is in more active dermal cells via

35:45 growth factors move through the primitive pit and move forward or we can say cranially toast up towards the pro quartel plate making this tubule process which is important for two reasons one is it induces the formation of neural ation the neural tube formation as well as becomes the adult remnant called the nucleus but pulsus right and we can also get a better idea of this in another view just to get an idea of how this trilemma inner disk is there along with the notochord and we already talked about the function or just just simple differentiation of these three layers which is again the ectoderm skin nervous system means the derm a lot of your connective tissues muscles ligaments bones and then on top of that the endoderm making a lot of the GI tract lining some of the accessory organs and glands I measure so in this video we covered everything that we need to know particularly for the gastrulation process and the development of the notochord and throughout these two

36:40 videos that we've already started we've already covered everything up until week two so what we're gonna do in the next set of videos is we're going to go into detail all the development of the embryo up until the third week and then we'll get into detail on the development of the as well if you guys like this video and if it did help please hit that like button comment down the comments section also in our description box so you guys can go there check out our Facebook Instagram patreon GoFundMe page any any help or any assistance whatsoever we would truly appreciate it I hope this video made sense hope you guys did enjoy it we love you ninja nerds and as always until next time [Music]

37:32 you