Understanding Placenta Development and Hormonal Functions

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

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