Embryology | Development of the Placenta

I ninja nerds in this video we are going to talk about the development of the placenta we're gonna get into a pretty decent amount of detail on that and then we're also gonna talk about the hormonal functions of the placenta and we'll throw throughout the video a couple clinical correlations that are important with this also before we get started check out the actual merch so we got a bunch of different shirts all kinds of Stuff you guys gonna go check that out that's down in the description box alright so it's going to get started alright

engineers so let's go ahead and get started then so when we talk about the development of the placenta it there's a lot of stuff going on so let's start from where we left off if you guys haven't already go watch again our video on cleavage we get to the end of that we start talking about implantation we're gonna kind of continue with cleavage Just basically just basically quickly like over viewing that and then we're gonna talk about implantation after we talked about the implantation of the blastocyst we're gonna talk about the differentiation of the trophoblast

then we'll talk about the formation of the extraembryonic coelom which will form or chorionic cavity we'll talk about how that chorionic plate is gonna be important for making the chorionic villi and aventure was called the chorionic Front dosam and how that interacts with the endometrial lining the decidua which helps us to make the placenta then we'll talk about the coverings of all the linings within the uterus with respect to the placenta the amniotic koreana chorionic membrane and then we'll finish off talking about the functions of the placenta so first things first that you have to

know if you guys remember where we left off we started taking up talking about in the ampulla the fallopian tubes Right you have the sperm and the secondary oocytes it was in metaphase 2 if you guys remember when they fuse you get the zygote and then we said that what happens is that that zygote that we have which has that nice little lining what was that nice little pink membrane that surrounds it if you guys remember that was called the zona pellucida okay so what happens from here this zygote starts to divide and if you

remember it went from a zygote and then divided into Two and these are gonna be called the to sell stage pretty simple right we give this better pink here and again those two cells are surrounded by the zona pellucida then it Cleaves again and it Cleaves into a total of four cells so then you're gonna get the four cell stage and again what's surrounding it you're gonna have that nice little beautiful zona pellucida again it Cleaves again when it Cleaves again You're gonna get eight cells right and then from here these guys is called eight

cell stage and again what do you have behind that around that you're gonna have that nice zona pellucida one more cleavage happens and you go from eight cells again just double one to 2 2 to 4 4 to 8 you're gonna go to 16 cells just for the simplicity I'm not gonna draw 16 perfect cells we're just gonna draw a clump of cells here and this clump of cells which is a hollow ball of Cells it's actually again gonna have that zona pellucida around it it's called the marula here's what's important with the marula the

rule is just a ball of cells but what happens is water so here's our marula and if again you want to remember to sell four cell stage eight cell stage marula is usually 16 or plus cells right then what happens water starts moving into the marula a lot of water moves into the marula and it fills up into a little cavity a Little fluid filled cavity which we call blasto seal so now if I were to cut this ball of cells this is what you would see you would see a group of cells on the

outer edge okay and this is going to be called the outer cell mass and then the water is going to push a bunch of the cells towards one edge here and they're all going to be mashed up against this center here so this outer part here is called the outer cell mass and then this inner part here is called the inner cell Mass and again what's going to be floating right in here in this little blasto seal that's going to be our our Blastoise all right that's where the water is this makes our blastocyst why

is that important the outer cell mass is going to be called the trophoblast that's the part that makes the placenta and the inner cell mass is going to be what's called the embryo blast and as you guys have already seen that helps to make our Ectoderm our endoderm army's a term which forms the entire structure of the fetus so that's important what we need to know now though is how this little blastocyst implants and attaches to the uterine lining because if you guys remember what's the uterine lining there's three layers we're not gonna hit every

single one of them like we're not gonna write them all out but if you guys remember orange lining is the endometrium this lining right here just Like a like maroonish colored one that's the myometrium and then the most outer layer here we'll say which is this purple part that's going to be the peri metrium well we want is we want the blastocyst to invade only the endometrium that's what we want so what we're gonna do is we're gonna take a section take a section here and we're gonna zoom in on this endometrium okay so now

here we have our endometrial cells if you remember and this is Important usually with your Anatomy you probably may have heard of what's called the stratum base at las' but because we're talking about the part of where a female is actually ovulated there is fertilization we're gonna undergo what's called decidua lies ation all that means is what used to be called the stratum function allison stratum base Alice cells they get filled with a lot of glycogen they get bigger they have a lot of lipids and they just become bigger Cells that are more sustainable for

fertilization so we call them decidua so this bottom row the basement so if you imagine here towards this end that's going to be the basement membrane of the endometrium and this is gonna be the apical so apical here basement membrane here okay the basement part is actually gonna be what's called the decidua base Alice and that's just this part to this part that's all that is okay this is the part that replicates and proliferate and Makes this purple kind of gee layer here this purple layer here is actually made up of two zones if you

guys remember from Anatomy you used to call this the stratum function Alice right and this was the stratum basale going to call the decidua now this right here the decidua function Alice it has two parts to it so we're just going to call this right now we'll call it the decidua function Alice but again remember it's actually just going to be Important because that's the part where the actual blastocyst will attach and invade the blastocyst will not invade the decidua ViSalus if it does you can get really bad complications and that's called placenta accreta and

if it penetrates past the decision of this house and so the mom atrium you can get what's called placenta in credo and if it goes really really far past the mom each room into the perineum you can get placenta percreta and those are very Very bad conditions the only way to usually treat those is by just taking out the uterus after someone gives birth now you don't want that right so you only want the blastocyst to involve the decidua function Alice or as you might also hear the stratum function house how does it do that

in order for that blastocyst to attach and again what are we gonna have here we're gonna have this inner cell mass which we're gonna call the embryo blast right now okay that's Our embryo blast and then outside of this you're gonna have the trophoblast and again these are gonna differentiate and we'll go through that stuff a little bit later for right now just trust me that we're gonna call this outer part here this outer cell mass we're gonna call this the trophoblast and then there's bunches of cells here inside of it which are going to

be sandwiched by all this fluid here which is the blasto seal which is where all this fluid is Sitting here this is actually going to be the inner cell mass of the embryo blast right so outer cell mass is the trophoblast this inner cell mass is the embryo blast on the trophoblastic cells they have little micro villi little micro villi that allow for them to attach to these little like structures that are protruding from the decidua function you know that these things these are called microvilli but these little Things that are protruding from the endometrial

lining here these little purple gadgets these are called Pinot pods Pinot pods so we have here the pedo pods and these allow for a very loose attachment so imagine this blastocyst falls into the uterine cavity it's gonna start moving towards that endometrial lining it has to kind of get grabbed right so what grabs it and gives it a nice little loose connection so it doesn't fall out right we're just Talking theoretically here making it simple it's gonna get loosely grabbed that first grabbing is going to be by the microvilli of the trophoblast and the Pinot

pods of the endometrial lining okay that allows a loose attachment so we'll call this a loose attachment this provides a loose attachment pretty simple right well we have a loose attachment let's build up a very strong attachment so how do we do that we're gonna still have the Pinot pod in Microvilli connection let's come down here so now let's draw again our structure here and again we're gonna have the embryo blast here we'll draw this as a clump of cells and then outside of this you're gonna have the trophoblastic cells and that's going to be

the outer edge okay so again what does the trophoblastic cells have on them they have nice little micro villi and on the pinna pods those are gonna be allowing For a nice little loose connection all right the pinna pods a lot our nice loose connection okay so here we're gonna allow for peanut pod connection with these microvilli that's the loose connection but then guess what starts to happen on these trophoblastic cells they also express very important molecules which are called integrants let's draw this here in orange so here these guys are going to have these

really really important molecules called integrants so In Taggarts that's going to be on the trophoblastic cells on the Indomie tree aligning you're gonna have selectins and selectins are going to be these sugar molecules so you're gonna have these carbohydrate-containing selectins and some of these selectins might actually be covered with a little bit of collagen okay so sometimes you might see selectins and collagen now these two are gonna provide a nice tight attachment and if this is an adequate attachment There's going to be a release of specific types of chemokines by these trophoblastic cells so the

truffle blastic cells are released chemokines and that will stabilize this strong connection okay so again going back first connection loose attachment microvilli are the trophoblast with the peanut pods of the endometrium second one you get a stronger connection with the integrants of the trophoblast with the selectins or some collagen tissue of The endometrium once that happens the trophoblast released chemokines and these chemokines are going to stabilize this adherence mechanism and allow for this actual blastocyst to start invading into the stroma invading the endometrium it's gonna start sucking it in that is so darn cool right

alright so now what's happened is we've already allowed for this nice little blastocyst to start invading right when it invades it's going to start how does it actually do That so that's the next question we get attachment before we actually start completely invading and this entire thing goes into the endometrial lining particularly the stroma of the decidua function Alice it starts differentiating so now we're at the part we've finished implantation so we did the loose attachment firm attachment chemokines signaling implantation boom we're in right but how does it allow for it to really invade Into

that stroma and really set its place of where it's gonna be for a while how does it do that and that's based upon the differentiation mechanism so if you remember I told you I'm just gonna write it out here the trophoblast is gonna differentiate okay and it's gonna make two components alright one is gonna be called the Saito trophoblast the other one is going to be called the CIN Ciccio trophoblast there ain't no way I'm spelling that out okay the other Part is going to be the embryo blast and remember if you even want to

go back further than this the trophoblast was the outer cell mass and the embryo blast was the inner cell mass the embryo blast is going to be going to make you'll see later makes the ectoderm your endoderm and your miso term which is basically going to be the three linings that makes up the entire human fetus right so what happens is once this attaches the trophoblast starts differentiating and It makes these two cell light layers this green layer here as you can see this single layer of green cells that's our Saito trophoblast okay so trophoblast

differentiated and it made this layer here the site or offal blast but then here's what's really cool the Saito trophoblastic cells they start really proliferating really really fast and then their membranes start breaking down and their cytoplasm and the nuclei start fusing with other cells and they Make this big pool of like a protoplasm which contains no defined cell borders like there's no well-defined cell membrane it's just a pool of cytoplasm and nuclei that are fused together and a nice syncytium so you see all this blue protoplasm with all of these multinucleated it's a multinucleated

structure which is fusing the cytoplasm and proteins together that's called the sensation of truffle blast so this blue structure here is called the sense issue Of trophoblast the sense issue atrophic blast is so darn cool because it does a couple things one is it releases all those hydrolytic enzymes that allow for it to break down some of the stromal tissue and invade into the endometrial lining in that cool so and you get the attachment you get the differentiation you get this in Ciccio trophoblast what does he start doing releasing hydrolytic enzymes hydrolytic enzymes start breaking

down some of the surrounding Stromal tissue allowing for this thing to invade deeper into the endometrial lining that's pretty darn cool here's the second thing that's really cool remember that we're assuming that all this is happening right a week after ovulation we're trying to think about in a perfect situation if a female gets pregnant you don't want her to shed that light how do we prevent that because eventually what happens is the corpus luteum is going to degenerate right Corpus luteum will degenerate it'll become the corpus albicans and it can't make progesterone why is that

important because if you guys remember from the our physiology videos here's a little uterine blood vessel this uterine blood vessel is super dependent upon progesterone so whenever there is a decrease concentration of progesterone what happens to this vessel it spasms and it leads to ischemia to the surrounding tissue and then eventually That leads to it rupturing and allowing for the entire endometrial or ischemic lining of the endometrium to just slough off and that's when they start demonstration how do we keep this progesterone levels up good Olson Ciccio trophoblast has got our back so guess what

he does he knows that it's time that the estrogen progesterone levels will start dropping so he C creates a hormone called human chorionic gonadotropin human chorionic Gonadotropin or HCG will stimulate the corpus luteum and tell the corpus luteum to keep making progesterone and that increase in progesterone will keep these vessels nice and open and dilated in a line for perfect amounts of blood flow to the endometrial lining to prevent it from becoming ischemic necrotic and sloughing off in that cool and this will happen up to about 10 or 12 weeks into gestation where the placenta

will take over so that is what I want you guys to Remember here second thing Saito trophoblast since this your trophoblast right second thing embryo blast remember we started off with just that inner cell mass and we remember we're going to be a little bit more specific called the embryo blast eventually it does develop into the ectoderm endoderm and mesoderm but before does that it divides into two layers first which we call the bye lemon or disk which we have here these pink Cells is our EPI blast the brown cells are our hypo blast below

here this is our primary yolk sac and above the EPI blast is going to be the amniotic cavity okay this is what I want you guys to remember from this picture so we have implant 8 we have adhesion then since this your trophoblast promotes the invasion into the stromal tissue it actually secretes human chorionic gonadotropin which tells the corpus luteum to continue to keep making Progesterone so that this endometrial lining doesn't slough off and so that it remains nutritive lots of blood flow proliferative secretory lots of glycogen and lipids all to promote the growth we

also said embryo blasts will divide into the by lemon or disc okay so that's where we're at at this point what happens next so the sense is your trophoblast will continue to try to invade and spread throughout that stromal tissue but it'll start to form Some spaces in between these finger-like projections this one here this one here this one here so it's just a space of stromal tissue right so it's just the endometrial tissue here but remember what's in the endometrium lots of blood vessels right well these little spaces are called lacunae okay they're called

lacunae so they're just little spaces which are consisting of stromal tissue at this point in time okay between the sister trophoblast but you remember what Are these little things here they're blood vessels they're uterine vessels if you guys remember what are the vessels of the uterus that come in you get the uterine artery right penetrates the myometrium and then you get straight artery and then you get your spiral and coyly arteries these are gonna be all over this endometrial lining right guess what this doesn't issue your truffle blast does this sucker so darn cool he

releases a lot of These proteolytic enzymes and guess what it does to the blood vessel lining it breaks down the blood vessels and it allows for the blood to seep in to these little spaces so now the lacunae or the lack of nurse space is they get filled with blood and they become little interval of spaces that we'll talk about it ahead okay so again around day nine so we're gonna start here around day nine let's say day nine here you start to form These little spaces called lacunae or lack inner spaces in between this

in sitio trophoblast since this year trophoblast released specific hydrolytic enzymes that break down some of the uterine blood vessels and allow for that blood to empty into this lacunae now you have these little interval of spaces pretty darn cool right anything change with your embryo blast no and we will really care about that right now we're focused more specifically on the Sensation of trophoblast and the site of trophoblast okay so all that's changed from this point to this point is that the lacunae are filling up with blood okay you form these lacunar spaces and they

fill up with blood around a nine let's go up here let's go to the next stage let's say a couple days later maybe day twelve alright we're at day twelve now all that happens here is that these lacunar spaces we're gonna actually become a little bit more Specific and we're gonna call them interval of spaces now okay because they're gonna be bit in in between these like little syncytial villi so you're gonna get a lot of these lacunar spaces we're just going to call them interval a spaces now and they're gonna be filling up with

a lot of blood so inter villus spaces okay and they're filling up with a lot of blood here's what gets a little bit more interesting now if you remember we had since this year trophoblast is This blue structure with all the multinucleated protoplasm green is the site of trouble excels right then inside we had the amniotic cavity if you guys remember amniotic cavity was this blue part here and then down here was the primary yolk sac and then pink was the EPI blast Brown was the hypo blast the hypo blast cells and some books will

say even the yolk sac will start making a connective tissue Okay I'm Mesa derma type of tissue that is gonna be between the saito trophoblast and the amniotic cavity the primary yolk sac what is this structure you're called we call this extra embryonic tissue so this maroon shaped stuff which is gonna be very very important it is called extra embryonic tissue so let's bring this out over here we call this extra embryonic mesoderm extremely important and the reason why it's important is because this is gonna Lead to the formation of a what's called the chorion

okay and the chorion is a very important part of the placenta it's the fetal component of the placenta well we're going to talk about is the chorionic friend ozone so what i want to remember in day9 lacunar space is get filled with blood day 12 interval of spaces we're gonna just change their name a little bit they start getting full with a little bit more blood and you form an extra and beyond Agni so Derm okay between the site or trophoblast and this embryo blastic structure here okay let's keep going let's go to like day

13 okay day 13 day 14 all right so we're gonna go to like day 13 day 14 okay all right so now we're at day 13 14 you're looking here right and what do we see whoa what happened all that extra embryonic Mesa Dern what the heck bro it started breaking down so some of the extra embryonic music arts breaking down and You start getting these little septation x' they're like extra embryonic little set dates okay well what happens is eventually all the there's a space that forms between one layer out here near the site

oh trophoblastic layer and one in here which is forming near the amniotic cavity and the primary yolk sac okay this is going to be this space is called the extra embryonic silom which will become the chorionic cavity so what is this part here called it is called The extra embryonic coelom then you get two layers you get this outer layer here right that is going to be around the actual site of trophoblast this is going to be the important one this is the one that we need to know this is called the so mat Oh

cleric extra embryonic mesoderm one heck of a thing to say there right now just for simply you know being consistent the inner layer is called the splanchnic cleric part of the extraembryonic Mesoderm and you see this little stalk here that's connecting the somatic cleric to this plankton plurk that's called the connecting stalk okay so just for you know being consistent with everything this the most important part here is the extra embryonic coelom okay you used to just be all mesoderm the mesoderm starts getting broken down and some starts adhering to the outer part near the

side of trophoblastic layer and some adheres to the inner part near the Amniotic cavity and primary yolk sac the one that it hears innermost is the splanchnic cleric layer the one that hears to the outer part is the somatic Plurk layer of what the extraembryonic mesoderm what's the cavity in between the extraembryonic coelom what will that become the chorionic cavity okay just for to be consistent here I'll write this one out here so again what is this layer here the inner layer this is called the splanchnic Klerk Lair and then again this structure here between

the splanchnic lurk and the somatic lurk is called the connecting stalk connecting stalk all righty one more thing I want you to remember before we go into the remaining like weeks 3 all the way to like four to eight one more thing happens look at the side of trophoblast what is it doing it's sending out little projections so the cells are proliferating proliferating proliferating and they're Proliferating all the way out to the edge so what they do is imagine here here's your side of trophoblastic cells they're proliferating they're moving all the way out towards the

edge around again they're penetrating through see the blue structure there that's the sense issue of trophoblast they're penetrating through this incision trophoblast and then they're proliferating around the edge around these interval spaces so they move Through going up through the sensation of trophic bus penetrate through the sensation of a blast and move out around the actual interval spaces one more time just for simplicity sake moves the set of trophoblast moves up through this in Scituate refer blast penetrates that since this your triple blast moves outwards and again surrounds the interval spaces what is this shell

here if you will around the interval of spaces that's going to be the site of Trophoblast coming through penetrating through it this is called the outer Saito trophoblastic shell pretty simple right so outer Saito troph Oh plastic shell okay and then simply simply what is this one the inner side of trophoblastic shell super simple right so that's what I want you to remember in date thirteen fourteen two things one you get a coelom second thing the actual Saito trophoblast moves outwards making this primary villi primary villi because It moves through these since issue trophoblast penetrates

and say outer saito trophoblastic shell so what are these things right here just this little this kind of villus here that is a primary villi primary villus that is important so three things actually I want you to remember one you get the primary villus second thing you get an extra embryonic coelom third thing that primary Villas breaks through the sense issue Atropa blast surrounds The interval of spaces as the outer side of trophoblastic shell okay we move forward a little bit more alright so now we finished off talking about how we get the primary villi

the extra embryonic coelom and then we also talked about the outer side of trophoblastic shell so again you're gonna have the outer side of trophoblastic shell here surrounding your interval spaces look at it penetrating through this incision trophoblast right so that was originally There was just this green structure which used to be the primary villus throughout the process of week three okay so week three and then forward okay we'll say week three maybe even go as far as to about week eight okay is when we're gonna probably in all this villa system here so we're

trying to make this chorionic villus system but it gets really cool okay so we had the primary villus what was the primary villas made Of I want you to remember this primary villus was just Saito trophoblastic cells that's all of us it was moving its way up through this issue atrophic blast penetrated made the shell the secondary villus remember what we had we had this maroon tissue remember it was making that somato pleura claire told you was gonna come in handy the somatic pleura Claire guess what it starts doing it starts invading in between the

Saito trophoblastic cells in between that Primary villi remember it used to just be a green line here going all the way up well now look what happens the somatic cleric layer decides it's going to invade inside of the primary villus so there's a core imagine here's my hand right that's going to be the somatic lauric layer covering that is going to be the Saito trophoblastic cell and then covering that is going to be the sin Ciccio trophoblast excels because look here's the core that's Going to be the again the mesoderm the extraembryonic mesoderm the somatic

cleric layer surrounding it is the Saito trophoblast the green and then what's surrounding that this is your trophoblast well what happens to the side of trophoblastic bliss all cells it still penetrates through the since issue Atropa blasts and forms a shell around those interval spaces in some areas it doesn't and that's where you get these things we'll talk about very briefly Later called anchored villi and floating villi so in other words if you don't have this anchoring it to the outer side of trophoblastic shell guess what it does it just kind of floats around right

but if it's anchored it's not gonna move right so that's the kind of a big difference there and it's just a difference in micro anatomy kind of stuff okay microscopic structures alright good so again what I want you to Remember here the extraembryonic mesoderm starts invading and where this primary villus is and now this is a secondary villi so now you're gonna get your secondary villus so secondary villus is again all I want you to remember is the somatic Plurk part of the extraembryonic mesoderm surrounded by sight of trophoblastic cells surrounded by since the trophoblastic

cells and again you're filling this chorionic I'm sorry you're filling this Interval of spaces with all that uterine blood vessels it's just starting to collect there okay beautiful stuff now throughout week three what are we doing we progressed from primary villus to secondary bills how does it get any better well guess what happens extraembryonic mesoderm if you guys remember Mesa durum can form blood vessels so guess what starts happening those Meisel dermal cells they start differentiating and they make Capillaries small little capillaries so capillary start forming all over the place so what do we have

here in this part notice that again you see these little these uh maroon like projections that's still going to be your extraembryonic mesoderm it's penetrating in surrounded by the green which is the saito trophoblastic cells surrounded by this blue which is the since cg.o trophoblastic cells what's different though again some of the extra embryonic Museum gets converted into blood vessels what are some of these blood vessels okay let's let's talk about this now so imagine here right imagine here we have kind of like a villas here okay here's a part of the chorionic plate so

here you're gonna have your chorionic plate here this is a thick part of chorion this is your chorionic plate okay and off of this chorionic plate you get these chorionic villi which is gonna make what's called your chorionic friend Owesome from here right it's connected through this umbilical cord so here you're gonna have your umbilical cord and the umbilical cord is gonna have two umbilical arteries and one umbilical vein right so this is usually by like the end of week three you start to get this embryonic folding so we're just trying to show you that

now at this point at the end of week three you're already gonna have this embryonic folding okay but now it's no longer Connecting stalk it's actually going to be the umbilical cord so we have the umbilical cord here okay and in the umbilical cord it used to be at just extraembryonic mesoderm right remember remember it was just this it was the connecting stalk but then what happens is you start breaking down some of that and then you're gonna have it become blood vessels so again that's what happens the extraembryonic mesoderm which was a part of

the connecting stalk Is actually gonna help to make the umbilical cord that's gonna start converting our differentiating into blood vessels what kind of blood vessels does it differentiate into two umbilical arteries guys write that down so what do you have running in the umbilical cord you have two umbilical arteries and one umbilical vein running through there from the umbilical arteries they move out into the chorionic plate in these arteries here which are on this Chorionic plate or called the chorionic arteries okay so then you're gonna get these chorionic arteries then they'll move up into these

villi and become actually what's called cotyledon arteries okay so again a blood flow from the fetus you're gonna have through the umbilical cord is the umbilical arteries they're gonna move out and become the chorionic arteries chorionic arteries will move into these actual chorionic villi and Make the cotyledon arteries now here's where it's really cool the only thing that's changed here is that instead of this being all extraembryonic mesoderm we have blood vessels within the center of it okay we have blood vessels into the center of this so these are just now going to be our

tertiary villus these are torre airy chorionic villus now again if you were to kind of zoom in on this imagine here we have the chorionic membrane here here's the umbilical cord Okay here we'll draw a couple we'll draw another villus here and we'll have another villus here what do we have coming up through here through the umbilical cord we're gonna have two umbilical arteries okay they're going to branch out into the chorionic membrane and form the chorionic arteries from the chorionic arteries they're going to branch into the villi and these are gonna be called the

cotyledon arteries what's surrounding just to be consistent Here what's surrounding this extraembryonic mesoderm saito trophoblastic cells and then what's surrounding that this incision triple blast and then what's here in between this villi and this villi in this villi blood what kind of blood maternal blood which is in these interval of spaces now here's where it should all come together guys guess what's happening here between this exchange so this is where the fetus Is dropping off its co2 it's dropping off its urea it's uric acid all the breakdown products it's picking up oxygen it's picking up

glucose amino acids lipids water soluble vitamins even antibodies like IgG antibodies - a lot for passive immunity and sadly and sometimes we obviously know that there can be the transfer of viruses and bacteria and parasites right we'll talk about torch infections very briefly but this is what's so cool so when we talk About by the end of like week 3 getting ready to go into week 4 what do we have this is our tertiary villus this is the exchange system and it's like this until about week 20 all that happens at week 20 and we'll

talk about that is you your your site of trophoblastic layer it regresses it breaks down that's all it happens but this is your placenta so your placenta is basically this structure here and there's also again--there decidua at this house but The whole purpose of here is just looking at the exchange process what do you have to move through well in order for the stuff to go from the mother's blood to the fetuses blood it has to go through this incision your OVA blast through the site of trophoblast through the chorionic lamina and then into the

actual baby's blood vessels an opposite would have to go through the baby's blood vessel through the chorionic actual tissue here and then through the Site of trophoblast through this institute ROFL blasts and into the maternal blood so that's pretty cool to see how that all works out ok so by the end of week 3 let's say like by week 4 you're gonna have your tertiary villus ok and it's gonna be like that for a while the only thing that chain along the way is a couple things okay one thing that happens maybe around the fourth

or fifth month of gestation is you get these things called placental Septa okay so tissue from the decidua line starts branching in okay so imagine here there's gonna be a placental fissure placental fissure there's a septa that moves all the way in here and all it does is it separates some of the tertiary villi to only be in one little area so now you're gonna have tertiary villi just in this area tertiary villi and this area it's basically housing tertiary villi in two separate little rooms that's all it is In those separate rooms which can

consist of maybe two or three tertiary villi are called cotyledons that's all it is cotyledons is basically going to be formed by this deciduous septa which separates out maybe two maybe three tertiary villi into individual little chambers okay that is what your cotyledons are so it's just going to be a little bit of a specialized like separation stuff like kind of structure So cotyledons and you get about 15 to 20 of these you get out 15 to 20 cotyledons so around the fourth or fifth month the only thing that's changing is that some of the

decidua you will form septa that separate out some of the tertiary chorionic villi maybe only two or three per septation okay and these are going to be these little septation x' where the decisional tissue will get more swollen fill up with glycogen fill up with lipids and it'll just become a Little bit more enlarged consisting of maybe two or three tertiary chorionic villi that little area is called a cotyledon and you get about 15 to 20 cotyledons generally that happens maybe fourth or fifth months so this is around the fourth or fifth month okay you

can get these cotyledons but we've already kind of pretty much defined our structure of the tertiary villas right the tertiary villas we already kind of just find this pretty Darn well what is this little maroon membrane here that's the chorionic membrane right what's running within that the nice little chorionic vessels and cotyledon vessels okay what's surrounding the actual blood vessels well again you had the chorionic tissue the extra embryonic tissue then you have the side of trophoblast and this is sis your triple blast and then again you're gonna have your interval Spaces and again this

is where the exchange is going okay remember I told you that it changes this is usually you know anywhere less than 20 weeks okay so it's usually from week four until about week 20 okay greater than or equal to twenty weeks gestational age what happens is the Saito trophoblastic layer regresses so you lose that Saito trophoblastic layer so that's all that happens is that the Saito trophoblastic layer Saito Trophoblast regresses that's all that happens around week 20 and it just becomes a thinner membrane to allow for more efficient exchange that's all it is because now

look instead of you having another layer there you're down one layer and it's just going to allow for a very quick and more efficient exchange process by decreasing it a layer okay so again where we left off primary villi around days thirteen fourteen usually forms along with the extra embryonic Coelom and again what we have here is the outer side of trophoblastic show again week three beginning from week three going all the way to about week four it progresses from primary villi to secondary villus which is just the sight of trophoblast with the core of

extraembryonic mesoderm particularly somatic pleura claire from there it progresses to a tertiary villus which is where all that happens is this extraembryonic mesoderm starts getting Converted into special blood vessels okay also the connecting stalk will actually start to become the umbilical cord and again that's filled with extraembryonic mesoderm so it gets converted into blood vessels what kind two umbilical arteries one umbilical vein okay and again that's gonna be surrounded by the amniotic cavity if you really wanted to know that okay but tertiary Villas is usually formed by the end of week four we said that

the Tertiary villus it really doesn't change much okay all we said is that by the fourth or fifth month you form these things called cotyledons and if you remember that's basically when the decidua tissue forms septa that's separate out maybe two maybe three tertiary villi into one little compartment and again the decidua cells get swollen they get filled with a lot of fluid they get filled with cholesterol glycogen lipids and they Become this big swollen little area which we call a cotyledon and you get about fifteen to twenty cotyledons around the fourth or fifth month

if you also want to be a little bit more specific we said that generally the tertiary Villas is these layers that we described the extra embryonic tissue Saito trophoblast since this year trophoblast interval of space right that's really just the layers that we were talking about usually between week Four to about week twenty if we get after week twenty we want the exchange to be a little bit more efficient so all that happens is that we get rid of the site of trophoblastic layer one more thing that you should remember and I talked about it

briefly is that around wheat from week four all the way to about week eight the only thing that's changing with the tertiary villi is that they start branching more again all that's really happening here from weeks Four to about eight is the villi become more extensive so what does it mean it's really simple here's just one villi right and within the center of that you have if you really want to remember around it you have the site of trophoblast around that you have the sense is you trophoblast and then again within the core of it

you have the vessels right here's your artery arterioles little capillaries there right so super simple structure Throughout weeks four to eight the layers still stay the same the only thing that changes is that this becomes more branched so then instead of it being just like one little thing it like branches into multiple extensions but it's still covered by what Saito trophoblast and it's still covered by since this geo trophoblast and in the center of it it's still gonna have the vessels well what are you doing here by making it more branched you're Increasing the surface

area so you're increasing the surface area for exchange so that's all that's really happening is from weeks four to eight it's still the same layering that's not changing it's just it's becoming more branched of a structure to increase the surface area for diffusion okay and transport of different things so we end of week four you have a tertiary villa system if you really want to be specific from weeks four to eight it's still the same tissue Linings but it becomes more extensive around the fourth or fifth month you get cotyledon formation which is just separating

these villi into multiple different little chambers fifteen to twenty of them okay and that puts a bunch of different villi within a little individual chamber okay and a lot of the cells blow up they get big fill cholesterol water glycogen lipids I've already repeated like million times right and then the last thing is after 20 weeks your cider trophoblastic layer regresses to allow for the exchange even more efficient okay and that means Capisce all right the last thing that we got to talk about here is that we are before we get into the basic functions

is just these linings I want you guys to be aware of these linings real quick because we're talking about this in a very zoomed in microscopic type of view but I want you to get an idea of what it kind of looks like from a bigger view Okay so here we have the uterus and inside of the uterus you've got the baby right so there's the baby okay then what do we have here that's connecting the baby to the actual uterine lining there this is going to be the umbilical cord right so that's our umbilical

cord and again if you remember running within that if you really want to be specific you have the extra embryonic music term and that runs out here and then you get your chorionic structure there okay So what do we have here we're gonna have the umbilical cord and then here you're gonna have this little wavy membrane and this wavy membrane is basically a bunch of these structures that's really what it is it's a bunch of these structures that are protruding into the uterine lining and this is called the it's the chorion because this is basically

the chorionic villus tertiary chorionic villus but all of them together make up what's called the chorionic front dosam Okay so it's called the chorionic front ozone which is all this extensive tertiary villi structure that was derived from the chorionic plate protruding and interacting with the decidua lining second thing is again what is this orange lining that it's supposed to be interacting with this is called the decidua base Salus and the decidua base Alice and the chorionic friend ozone guess what they make the placenta the chorionic from dosam is This of tertiary villa system that's the

fetal component and the decidua basalis with the interval spaces is the maternal component those two combinations make up the placenta the other part here is again your this blue membrane is the amniotic membrane the red membrane is the chorionic membrane and then you have this little orange membrane that's surrounding the chorionic membrane of the chorionic plate here and this is going to be called the decidua capsule Aris so this one right here is called the decidua capsule Aris and then the one where there's no attachment or no fetal involvement is called the decidua pariah Tallis

eventually as the fetus get grows and grows and grows and grows the decidua capsule heiress will fuse with the decidua pariah dallas and obliterate the entire uterine cavity so that's eventually what will happen over time okay one last thing here just so that We're super Lake specific chorionic friend ozone is this part of the chorion interacting with the deciduous alice making the part of the placenta the chorion over here it doesn't have a lot of this kind of like since this yo trophoblastic structure in this last nice little villi structure that breaks down and becomes

a very thin very flat membrane which we call the chorionic leave so this membrane here this part of the chorion that's on the Abba embryonic Pole over here this is called the chorionic leave okay so that's important to remember so what I want you to remember out of these structures decidua capsuleers is surrounding the chorionic membrane here the chorionic leave if you want to be specific decidua basalis is interacting with the chorionic friendo ISM those two combinations together give you the placenta and in the part of the decidua that's not interacting with any part of

the fetus Okay or the placenta is called the decidua parietals but do realize as the fetus expands the decidua capsule errors and the decidua pariah talus will fuse together and obliterate any part of the uterine cavity okay Coriana cleave is again this part of the chorion where there's no extensive villi system all right so what are the functions of the placenta in a very basic way because we've talked about a lot of stuff of the development Of the placenta it's an extensive amount but what I want you guys to understand is the metabolic functions of

a placenta so very simply when we talk about the metabolic functions remember that it's primarily playing a role in gas exchange so this what do I mean so it's actually gonna be dropping off oxygen right so it's dropping off oxygen to the fetus and then here's gonna be from the mother dropping off oxygen and picking up co2 that's one Simple thing the other one is is going to be delivering nutrients so nutrient delivery and some of these nutrients can be delivered very simply through like a simple diffusion process but truly it's mainly the gases most

of it is going to be like facilitated diffusion or some type of active transport but this is gonna be things like glucose amino acids fatty acids even water soluble vitamins so the B vitamins okay and even I G G antibodies now a lot of these are taken Across the actual placental membrane by either facilitated diffusion like glucose a lot of them are done via some type of you know active transport or pinocytosis type of mechanism one of the big ones is IgG antibodies why is this important IgG antibodies are important because they help to confer

what's called passive immunity okay in other words these are antibodies that the mother has already made against specific types of Pathogens of some form and is allowing for the fetus to have those antibodies so that they can be protected against multiple different types of foreign antigens whenever they're exposed to it so that's the beautiful thing as a vaporizer this now kind of a natural passive immunity for the baby in some ways this can be extremely dangerous and one of the dangerous things is there is a condition where certain IgG antibodies particularly that are against RH

we call Them the D that you know the duffy antigen if you have these rh d immunoglobulin IgG antibodies that the mother makes because she's Rh negative and they she had a baby previously who was Rh positive or the mother was Rh negative and she had a spontaneous abortion of a baby that was already positive what happens is the mother produces antibodies against those red blood cells that are RH antigen positive and can Cause destruction so this is a really very dangerous one that you have to be careful with that's why whenever somebody does have

this okay like a mother okay if they're trying to protect them there is a medication that you can give which is called Rogan and it's basically an anti AGG antibody that are erected against the RH antigens they give this to mothers who are Rh negative and a baby's Rh positive so that way whenever the placenta breaks away right During the actual third stage of delivery whenever some of that blood does escape into the mother circulation there isn't this immunological reaction we can block it okay if not and the mothers already a low immunized we have

to check the baby's middle cerebral artery blood flow and they do that through a Doppler and they calculate velocity based upon fetal anemia we're not gonna give it to all of that or though right now okay so that's some of The big things now there is unfortunate things that can be transported across the actual fetal membrane that we have to be aware of and you want to remember that as those that what they call it the torch series so you can remember T o r CH so T is toxoplasmosis okay this is toxoplasmosis gondii and

it can actually cross the placental membrane as well cause significant fetal defects and damage and it's extremely dangerous usually if someone does have This you try to treat them with spear Meissen unless the babies have been infected they need to treat them with another drug called / methylene and sulfadiazine but again this is something that you want to be careful of it can cross that placental barrier others so what do we mean here this could be things like HIV this could be things like syphilis it could be things like hepatitis particularly hepatitis B virus these

are also other things that can be Transported across the placenta don't like that our rubella rubella is a very dangerous ones that can cause a lot of cardiac and congenital defects as well like hearing loss okay see CMV cytomegalovirus this is another one that can cause a lot of problems as well and then H is going to be your herpes simplex virus okay and this could be like you know type 2 so these are some things that you have to be very very careful of and another Really really dangerous one that people are actually should

be aware of nowadays is Zika virus okay the Zika virus does have the capability of being transferred but vertically as well so don't forget also about the Zika virus so these are some things that can actually cross the placenta and we have to be very careful of there's many other kinds of Molokini bacteria like Listeria monocytogenes that can come from like Pasteurized like products and very like you know cold like meats like lunch meats but again for the most part the ones you have to worry about is the viruses they have the ability to cross

that placental membrane okay so big big functions gas exchange nutrient delivery okay and what else okay waste waste removal okay so they remove a lot of different things like urea uric acid okay and and so on and so forth okay more different types of waste Products that's not super super and integral to this lecture okay what else so we got metabolic functions and hormonal functions this is a big one it makes a lot of different hormones but what are some of the big ones what are some the big big ones so one of them is

estrogen and progesterone right we talked a little bit about these that they were made a little bit later you know Mort around towards like we could say generally around the 10th to 12th Week of gestation right and what what is their big function here if you guys remember they are going to take over for the corpus luteum of pregnancy and tell the endometrial lining to thicken so it's going to thicken up that lining providing a very nutritive environment by increasing the bullet the vasculature to this area making sure that the baby gets enough nutrition so

it's going to increase a lot of the secretions and it's going to make sure that the baby is Not and harmed in any way or affected by anything from the external environment so it's going to plug up that cervix right with a big old mucus plug so those are some of the things that it's really going to provide as well as just very simply development of the fetus so it's also going to play a very crucial role with development of the fetus what some other things well another thing is it can make you can get

thyroid hormone okay in addition to from the placenta Which makes a little bit you can also get this from the maternal you know thyroid hormone as well so thyroid hormone what is it going to do big big thing here is it's going to promote the development of the central nervous system this is extremely important so it plays a role in CNS development as you guys know with a lack of thyroid hormone there's a risk of ism which is a complete incomplete development of the central nervous system which can lead to Mental retardation are what else

another one this one's actually pretty very cool human placental lacta Jim what human placental lacta gene does is is it does a couple things it inhibits it basically decreases insulin sensitivity right so it alters the insulin release okay so it's going to alter insulin release from the pancreas it's also going to act on the mothers cells so this is going to be the moms cells s can do a couple things one is this gonna promote lipolysis Which is going to give a lot of fatty acids for the baby it's also going to promote gluconeogenesis so

gluco neo Genesis and this is basically going to provide lots of glucose for the baby and lots of fatty acids for the baby okay but here's another thing it does - the mom sells it makes the mom sells resistant to insulin so even though the moms going to produce insulin it's gonna try to decrease insulin production but Even if there is insulin production the moms cells are gonna become resistant to the insulin so that it doesn't shuttle all this glucose back into the mom cells so now why is that important you're gonna have lots of

glucose lots of fatty acids to deliver to the fetus across the placenta what a beautiful mechanism that is okay another one is called relaxin and relaxin is basically what it does it relaxes specific ligaments of the pubic Symphysis so it relaxes the ligaments it increases the laxity of those ligaments the particular one is the pubic symphysis why is this important you want to widen out that actual pelvic Inlet right and pelvic outlet so that you can allow for a big ol baby to come plunging through there what else it also can make corticotropin-releasing hormone in

addition to the mother's pituitary gland making it this is important because it plays a role in the Production of cortisol eventually CRH stimulates ACTH what stimulates cortisol production cortisol is important because it plays a role in lung development and surfactant production so why is that important if baby is born all right cortisol production is usually the highest around the 34th week so if for some reason the baby is actually going to be having like it's a preterm labor they premature rupture of the membranes let's say preterm premature Rupture of membranes so it's before 34 weeks

let's say that cortisol is not going to be high enough for a lot to allow for surfactant production the lungs are going to be completely ready to go what that means is if the baby's born without having that proper surfactant production those alveoli are going to be collapsed and it's gonna be almost near impossible for the baby to get enough strength through its diaphragm and intercostal Muscles to pull air in to pop open those alveoli and that's going to lead to what's called infant respiratory distress syndrome so that's why it's important that we have enough

cortisol especially around the 34th week so we can get that surfactant production nice and high so we get good fetal lung development iron in areas so that pretty much covers everything that you guys need to know about the development of the placenta and the function of the Placenta I hope it made sense and I know it was a lot of stuff that we went through a lot of drawings but I really hope that it made sense and it hit home the point of everything that you guys need to do well in your exams to do

well in future practice if you guys did like this video and if it did help and if you guys did enjoy it please hit that like button comment on the comments section and please also subscribe if you guys are interested in getting into contact With us just want to talk to us we have a Instagram we have a Facebook we also even have a patreon account we have again links to all the merchandise that we have down in the description box go check that out and any help that you guys can provide we would truly

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