Embryology | Fertilization, Cleavage, Blastulation

iein engineers what we're gonna do in this video is we're gonna begin our embryology series okay so if you guys haven't already we're gonna start from the end of fertilization which is on a reproductive playlist if you guys haven't seen that already go watch that first we're not going to go into a ton of detail on that we're kind of just going to skip over pieces and begin the development within the first week then after that what we'll do is we'll go into the next video which is going to be the development up until the second week right so we're gonna go for gastrulation then we'll have another video what we're going to the development during up to week three which is gonna involve dinner elation process and then we'll discuss the the formation of the nervous system and we'll just continue to keep going from there until the development of the entire embryo alright so let's go ahead and get started I'm user so let's go ahead and get started then so first off we have to talk about before we kind of get into all the cellular events I want us to really kind of correlate our Anatomy with kind of the bigger picture then we'll get down to the cellular events so if you guys remember from the fertilization video just a little bit about your uterine anatomy right so very simple here there's gonna be the vagina they also call it the sheath right then you're gonna have this portion right here right which is called the cervix of the uterus then we'll kind of get into the body of the uterus right here up this top like portion here which is kind of rounded out like that that's gonna be the fundus of the uterus and then here you're gonna have your fallopian tubes right and then at the end of the fallopian tube you kind of have this little dilated region right there that's called the ampulla of the fallopian tubes that's where fertilization is supposed to occur right then you got your little fingers little same brain right and then after that you got the ovaries right so what's important is that an order for us to really kind of talk about the cellular events we have to understand the physiology going into this so what happens usually around day 14 or day 15 of a female's menstrual cycle right I'm sorry they start to release a specific type of hormone right called luteinizing hormone so if you guys remember here let's draw like a little diagram here we're gonna have this guy but you guys remember this diagram it's pine grain into your brain right now we're gonna have the hypothalamus with the poster pituitary and anti pituitary that's not nutsacks okay so just remember that now what happens the hypothalamus starts releasing specific types of neuro peptides what are these neuro peptides called they're called ganado tropen releasing hormone and then what is gonna a - open releasing woman do lots of it - it stimulates the anterior pituitary what does it tell the anterior pituitary to do it tells it to start secreting large amounts of luteinizing hormone alright and this is also kind of playing a role not just with the GnRH but if you guys remember a little bit back from you're kind of the dimensional physiology there's also another very big trigger here and that's going to be a sturgeon if you guys remember that positive feedback cycle when estrogen levels increase again right during the second time that's also a big stimulator of luteinizing hormone as well all right anyway luteinizing hormone it's released it gets into the blood goes down to the over what does it do well if you guys remember it tells the ovary to kind of start producing a lot of fluid alright so it tells the ovary start making a lot of fluid but pressurize that follicle because remember we have that graafian follicle which is the guy who's gonna have that secondary oocytes what does he do he triggers the release of certain types of prostaglandins to dilate the vessels to increase a lot of the leakiness out of the capillaries around that graafian follicle and activate certain types of enzymes metalloproteinase is to break down the connective tissue around it and guess what that helps helps to pop that little OA site out and then what happens is the fimbriae they get all kinds of cool and they start kind of moving that actual oh a site towards what the ampulla then this little oh a site here we're going to draw it right here and here is going to be the corona radiata around it it gets popped out here right so now that's our secondary oocytes I think eyes remember I talked about it and the kind of the whole ovulation cycle that this is the secondary oocyte what that means is if it's are undergoing meiosis one and it's getting ready to go into meiosis - right it's getting ready to finish meiosis - but it hasn't yet what stage is it particularly in well if you guys remember we said that once it's ovulates it's stuck in a specific phase it's a secondary Oh a site in metaphase - that's an important thing to remember secondary oocytes stuck in metaphase - the reason why is it's waiting for a sperm cell to touch it and then once it does it says oh what I need is here I'm gonna go ahead and finish meiosis to get myself prepared for this nucleus from the sperm cell and then I'm gonna fuse with it so it's waiting and waiting and who is awaiting on it's waiting on the lucky son of a gun right who gets the sperm cells where they need to go and what happens is the sperm once it's ejaculated it goes into the vagina up through the cervix of the uterus up through the body it makes its way through the fallopian tubes and it meets that nice little secondary oocytes phase - at the ampulla all right and it says hey I want to go ahead and touch you now not in a creepy way though alright so it goes ahead and it touches it and then guess what starts happening well let's go ahead and dig into that so what we're gonna do is we're gonna imagine that these guys are touching one another right here in this kind of like zone we're going to blow it up and we're gonna take a look see so now we're blowing it up here and here we're gonna have that egg right so we have that secondary oocytes stuck in metaphase - this is the one then we got that sperm cell and that sperm cell is coming over here to meet this egg alright but in order for it to be able to touch it you guys remember it has to go through a process called capacitation where has to clean off a bunch of cholesterol molecules and things off of the head of it and then it has to attach to a specific type of protein on the surface and what is this protein if you remember we have what's called zp3 receptors and these zp3 receptors are really important because once the actual sperm touches so zp3 receptors once the sperm cell touches it it activates the sperm cell and then the head of the sperm cell whew with the zone with the oocytes membrane starts releasing a bunch of different enzymes lysosomes hydrolytic enzymes from its acrosome and it starts burrowing its way through this then what it does is it releases its nucleus you see this little green guy it releases its nucleus into the cytoplasm so here's going to be this nucleus now in the nucleus you know that there's chromosomes right 23 chromosomes are going to be in the sperm cell nucleus and 23 chromosomes are going to be in d.o.a sites nucleus well what happens is let's see here 23 are gonna be paternal and 23 of the other chromosomes are going to be maternal these are going to fuse when they fuse how many you gonna get was 23 plus 23 it's 46 right so you're gonna get 46 chromosomes now and this is going to be a diploid cell but we're also going to call it as I go so again how many chromosomes 23 plus the 23 23 maternal 23 paternal 46 total chromosomes and this is going to give us our zygote now it's pretty amazing when you think about it that from this one cell this one cell we're actually gonna be able to make an entire human body that's pretty amazing so how does this happen this zygote guess what it starts undergoing lots and lots of lots of proliferation so it starts going through achieve one sg2 mitosis and just starts replicating and replicating and replicating what is that call whenever it starts replicating and making two cells then four cells then eight cells then sixteen cells that's called cleavage so it's very simple we've already talked about fertilization now what do we have to go through we have to go through a bunch of stages called cleavage so it's very simple now now it's just a matter of counting it up now what I'm gonna do is I'm going to divide this cell it was once one cell guess what I'm gonna do now I'm gonna now have two cells now here's the important thing to remember remember I told you that this pink membrane had a protein called the zona pellucida three receptor that pink protein is called the zona pellucida so you're gonna have it in fertilization you're gonna have it in the zygote and you're so gonna have it in this cell where it divides what's this cell called this is now called the two cell stage it's very simple right so zygote you're gonna go into the two cell stage guess what it's then gonna do then it's then gonna divide again it's gonna go from two cells and you're gonna double that so now it's going to be four cells so let me do this now so there is going to be four cells so this is the four cell stage then what I bet you already guessed it it's going to divide again and it's going to turn into the eight cell stage and then what do you think it's going to go to after that it's gonna go to the sixteen cell stage so throughout that process now if you imagine we're gonna have eight cells here and then before you know we're not gonna draw in all sixteen cells here what you know here is that you're gonna have tons and tons and tons of cells and what this is gonna do is it's going to form a kind of structure which is very interesting what do I mean okay you're gonna have these cells and they're going to be surrounding the entire thing surrounding this entire structure right so it's entire circle you have these cells surrounding it but inside the center of it is hollow there's nothing in there okay so if you were to imagine let's imagine I took like a cross-section here here's going to be all the cells right forming the outer coat there's our cells forming the outer coat but inside of this there's nothing it's completely Hollow what do we call this anything from 16 cells and up until we get our blastocyst we call this the marula so we call this one the marula and this is basically going to be a hollow ball of cells which is going to be 16 or + cells and what they call these they'd like to give these cells a special name these little circular blue cells here once it's at the level of the marula they call these blastomeres blasto mears okay so that's important to remember now from here what's gonna happen then okay so now we have this marula right the marula guess what it starts to do it starts to take the cells right you have the cells right here forming the edge what's going to happen is a bunch of the cells in the center there's gonna be a bunch of cells that start compacting towards one edge alright so you're gonna have the cells lining the edge of this cell so let's do it like this here you're gonna have these cells they're gonna be kind of lining the edge and they're gonna form one type of cell structure that's very important because this helps to go on and form a part of the placenta okay then another group of the cells around that are gonna group towards one side and kind of clump together let's do that in a different color so that we don't confuse this let's do this in the screen here now we're gonna have these other cells and they're going to be kind of grouping together here and now we had a hollow ball now what we do is we have a cell lining around the edge and we had to have just a bunch of group of cells just clumped together in this one edge over here what do we call this this is going to be our blastocyst so the process of what we're going from the marula into the blastocyst is your blast chelation process so now what do we have here we're gonna have our blast chelation and we're gonna form here our blastocyst which is so darn cool now within the blastocyst you're gonna have this fluid filled cavity so it's going to be all fluid in here right but then this group right here this bunch of cells that are going to be kind of clumped here together this becomes a specific thing right we call this part here the inner cell mass okay and then the cells around the edge or the periphery of it this is going to be called D and very simple outer cell mass now what happens is these cells they start to differentiate and become more functional right and what happens is they become a little bit more differentiate a little bit more functional and then they become a different type of name we just like to change names for things all the time so now what happens they continue to differentiate continue to develop and now that outer cell mass becomes a specific type of thing which we call the trophoblast so now this outer cell mass is now what we call a trophoblast becomes a little bit more differentiated a little bit more specialized and we call this the trophoblast then we had that inner cell mass it starts to become more specialized and more differentiated and it turns into a specific thing which is going to be important and this is going to be called the embryo blast this is called the embryo blast so all I want you to really know is the outer cell mass becomes the trophoblast and the inner cell mass becomes the embryo blast why is that important because guess what eventually the trophoblast becomes which we're going to talk about next it didn't differentiate into two other specialized layers one is going to be called the Saito trophoblast which we'll talk about and the other one is to be going to be called the syncytium trophoblast the embryo blast guess what its gonna start developing into it's gonna start developing into your by lemon or disk so and we'll talk about how that happens but this is going to start converting into your bi laminar disk so within this first week right that we've talked about what happened we had ovulation was the first step right so let's go ahead and mark out down our steps first step was ovulating right second step was fertilization okay and that was here this was here and then continuing on down here this is still fertilization right so this is still the fertilization step then what happened from all the way from the zygote all the way until the sixteen cell stage this was all called cleavage so we'll write that down that was the third step okay then what happened after that then the next thing is the marula converted into the blastocyst okay that's going to be the fourth stage so the fourth step is going to be blast elation then after that the blastula became more specialized and converted into a trophoblast which used to be the outer cell mass and the embryo blast which we used to become d which used to be the inner cell mass then they will become even more specialized in the embryo blast become the bilaminar disk which is going to be the EPI blast and the hypo blast which we'll talk about and the trophoblast is going to become the Saito trophoblast and this is serial blast this is important because these help to be able to make to your structures like the placenta okay whereas the embryo blast is gonna make the embryo right so this will then go from the by laminar to the Tri laminar and that will help us to make our entire embryo so that's why this is so important this is generally occurring within the first week what we'll do next is we'll take this truffle blast excel with the embryo blast and we'll talk about how it sprouts these little things we'll talk a little bit more about this in seetio trophoblast with the villi and how it breaks through the zona pellucida and then we'll talk a little bit more about the embryo blast and how that converts into the bilaminar disk alright so we'll talk about that in the next video [Music]

Channel: Ninja Nerd

Views: 1,041,179

Keywords: embryology, fertilization, cleavage, blastulation, ninja nerd science, gestation, embryo

Id: 8-KF0rnhKTU

Length: 17min 37sec (1057 seconds)

Published: Mon Aug 19 2019