Transcript for:
Reproductive Systems and Pregnancy Overview

hello and p2 class in the past couple of videos we have covered um the male and the female reproductive systems going over the basic anatomy um and the hormonal regulation of um the gonads related to those different or uh organ systems like um in the case of the males talking about how the testes are controlled and therefore how they are regulated in terms of sperm production being formed inside of the seminiferous tibials um and with respect to the female reproductive system we discussed the ovarian cycle and and the uterine cycle and all of the different hormones that regulate those two processes the unifying concept uh was the hpg axis which was the relationship between the hypothalamus the anterior pituitary and then the gonad and the different hormones released from there like the gnrh being produced by the hypothalamus which then prompted the release of um fsh and lh from the anterior pituitary and then that targeted the corresponding gonad to either produce testosterone in the case of the males or estrogen and progesterone in the case of the females and so what we talked about with the female reproductive system was um during the ovarian cycle mid cycle there was an event called ovulation that occurred um and at that time a secondary oocyte was ejected from the ovary into the urine tube where we briefly um started our discussion on this topic the oocyte has the potential of being fertilized by a sperm when the sperm penetrates that oocyte then you see fusion of the 23 chromosomes from the sperm along with the 23 chromosomes from the the oocyte resulting in the very first cell of a newly formed individual so that's kind of where we need to pick back up with this particular um video in this discussion we're going to talk about pregnancy embryonic development and then leading to changes that occur during fetal development so we're going to kind of use what we've already talked about and the information that we've already laid as the foundation with the male and the female reproductive system i want to go forward in terms of defining fertilization and then what happens to that fertilized ovum implantation and all of the early embryonic developments that need to occur so let's um get started um so pregnancy is basically all the events that occur um the entire time period from the time of fertilization which by the way fertilization would be the fusion of the uh chromosomes from the sperm with the chromosomes from the ovum so that all the way from fertilization till uh delivery and birth of an infant that is what we define as a pregnancy so the early developing offspring is called a conceptus uh the very first cell that is formed as a result of fertilization is called a zygote and i'm going to show you a schematic putting all of this into perspective typically the gestation period is what we define as the time from the last menstrual period of a female all the way till the birth of that infant um and if you think back to the ovarian cycle the first two weeks or so of the ovarian cycle during the follicular phase that's when the follicle is developing that's prior to ovulation so therefore there is really no potential for um fertilization and a pregnancy really to occur during or whether during that early phase so therefore um if you define gestation period as the time from the last menstrual period uh then those first two weeks uh really prior to ovulation uh the female is not even considered pregnant uh although it is included as part of the gestation period and this is simply because of um ease of identifying uh for in most females most females can identify the the last menstrual period as opposed to the exact time of ovulation and possible fertilization with sperm so yes the gestation period does include the first two weeks of the ovarian cycle when pregnancy has not um theoretically occurred now um after the formation of after fertilization in the formation of the zygote um the uh which we can kind of also call the conceptus um all the way through week eight you you would refer to the developing conceptus as an embryo but from week nine onwards all the way to birth you refer to the developing uh conceptus as a fetus so uh let's go back to a few things that we've already discussed um with the previous chapter with the female reproductive system now the secondary oocyte that is released into the urine tube um as a result of ovulation is typically viable for a very short period of time about 12 to 24 hours during which time fertilization with the sperm needs to occur the sperm however has um a greater shelf life if you will um typically um 24 to 48 hours um and the sperm can be viable uh after uh ejaculation and after introduction into the female reproductive tract so in other words um the sperm can um so if a couple is intending to achieve a successful pregnancy then sexual intercourse could occur up to about 48 hours prior to the ovulation of that oversight and up to say maybe 12 to 24 hours or so um after ovulation has occurred um so um so that's kind of what's explained over here which is about 48 hours or so prior to ovulation but up to 12 to be on the safe side um maybe up to 24 hours after ovulation so we're going to define this event of fertilization and then track the journey of this fertilized ovum uh gonna define certain events called cleavage which are very rapid mitotic events divisions and that need to occur as the ovum continues on um approaching the uterus so fertilization technically is when the sperm's 23 chromosomes remember the sperm is haploid when the sperms 23 chromosomes combine with those of the secondary oocytes so 23 plus 23 making um a normal cell a diploid cell 46 chromosomes um basically um forming um the very first cell of this newly formed individual which we call a zygote um okay so in order to achieve fertilization the sperm has to go through several different steps and the most important thing really is something called capacitation so when uh when sperm is introduced into the female reproductive tract as a result of intercourse um quite a few thousands of those sperm cells um are lost because they are leaked out of the vaginal canal and some sometimes they're destroyed by um the increased acidic environment in the female vaginal canal as a lot of it is destroyed by phagocytic cells uh recognizing that those sperm really shouldn't belong in the female body considering them as uh intruders or um um foreign cells uh so therefore of all the ejaculated sperm uh only a few maybe up to a few thousand of those sperm actually survive uh as they move up the female reproductive tract through the vaginal canal the cervix then the lumen of the uterus and all the way into the uterine tubes the very first thing that happens is when um they are deposited in in the vaginal canal the sperm has to go through a process called capacitation where they basically regain energy and motility and then are able to make the journey towards the possible ovulated secondary oocyte and then be able to penetrate this oocyte now if you remember the structure of the sperm there were three different regions and there was a head region which contained the dna and that head region was protected by a helmet like structure called the acrosome that are filled with hydrolytic enzymes so there needs to be a process which allows for the release of those hydrolytic enzymes because those enzymes will then literally punch holes through the plasma membrane of the oocyte enabling the sperm to enter into the oocyte so i'm going to describe this process um and as the sperm makes its way through the different regions of the female reproductive tract um they literally sniff out chemicals that are released by the secondary or site in order to be able to reach that our site okay okay and then we're going to talk about uh the acrosomal reaction and the actual process of penetration of the sperm uh through the plasma membrane of the oocyte to accomplish fertilization so i'm going to discuss this idea of acrosomal reaction using the next slide i believe where we put this together using a schematic now if you remember the oocyte the secondary oocyte that was ovulated um actually has a transparent or a translucent membrane surrounding it like called the zona pellucida and then there were also several layers maybe two or three layers of what we call the corona radiator so that was the entire secondary oocyte that was ovulated so the sperm has to find a way through the corona radiator the zona pellucida before it actually binds to the plasma membrane of the secondary oocyte and for this uh to occur we need to discuss the acrosomal reaction now this is also a very important concept uh only one sperm is allowed to penetrate a secondary uh or site and this is called monospermy uh actually multiple sperm are blocked from penetrating the same oocyte and this is a very important concept called block to polyspermy because if you kind of think about it if multiple sperm are allowed to penetrate and oocyte then you have more than 46 resulting chromosomes in that zygote that's formed and that would be an abnormal cell that would be marked for destruction and so then you would have a spontaneous abortion um of that abnormal cell that's being formed okay all right so here's the schematic i was talking about this is a very important um schematic that kind of puts together many different concepts so let me kind of set the stage here so what you're looking at here is a secondary oocyte rather large uh so here's my um the dna kind of contained inside um this is actually a few stages ahead but you would imagine that that was a secondary oversight um with its 23 chromosomes here's the zona pellucida in that grayish kind of layer surrounding it and the few layers of the corona radiator cell so this was what was ovulated um in the in the female from the ovary into the uterine tube uh and then you're looking at uh hundreds of sperm cells approaching um this secondary oocyte all racing to uh be the first one to penetrate that secondary oocyte so let's kind of zoom in a little bit more and you can look at that region right here this if you kind of zoom into this region it looks something like this so here's a corona radiator all of those layers of cells the zona pellucida as this grayish layer is a plasma membrane of the oversight and of course this is the interior of the oversight the secondary oversight so what needs to happen first approach so the sperm cells are approaching it's pretty easy to get through the corona radiator i just basically makes its way through those layers of cells and then it enters or kind of reaches the zone of pellucida this is where we trigger something called the acrosomal reaction so binding of the sperm to the zona pellucida causes calcium levels to increase inside the sperm triggering the acrosomal reaction what happens here is that those enzymes in the helmet-like acrosome region of the sperm those enzymes are released and what that what those enzymes do is that they start to kind of punch holes or kind of allows for the penetration of that sperm to get past the zona pellucida uh making its way all the way to the plasma membrane of the oocyte that is what we call the acrosomal reaction once um if we can kind of imagine this sperm here once the sperm makes its way through the zona pellucida and actually reaches the plasma membrane this is where the sperm binds to the plasma membrane of the oversight at this point [Music] we need to talk about this last step here which is the blocked polyspermy so this is okay so once that first sperm the very first sperm that is able to actually get through this process of binding to um the plasma membrane then you want to basically prevent other sperm cells that are very close but not quite there yet you want to block all of those sperm cells from actually penetrating into this oocyte and this is what we call blocked polysperm so this last part here is zoomed in a little better using this this slide right here so what happens is as soon as that sperm makes contact with the plasma membrane of the secondary oocyte the secondary oocyte uh starts to release something called cortical granules so this is what we call the cortical reaction this is also in response to a calcium surge except this is occurring inside of the secondary or site when those cortical granules are released um what happens then is that that uh entire plasma membrane and the zona pellucida basically it hardens kind of like becomes like a cement like layer and what then happens is that all of the other sperm cells basically get clipped off are preventing all those additional sperm cells from entering into this uh and into the interior of the secondary oxide okay so this is what we call block to polyspermy this um determines or this uh makes sure that uh only a single sperm penetrates and actually has a capability of fusing with the chromosomes uh within the oocyte so it enables monospermy and uh prevents poly [ __ ] okay as soon as um as you can kind of see here in this picture as soon as this uh cortical reaction occurs then uh the rest of the sperm like the flagella and the mitochondria for the most part is uh does not really enter into the interior only the nucleus really is released into the interior of the secondary oocyte where um it then as soon as that the sperm nuclei enters into the secondary oocyte it the secondary oocyte will immediately complete meiosis too remember the secondary oocyte was uh kind of stalled or arrested um in metaphase two so it hasn't yet completed meiosis too it's only penetration of the sperm um into the secondary oocyte after it gets past the plasma membrane of the oocyte it's only that and then that calcium surge that's occurring as part of the cortical reaction that triggers the completion of meiosis ii and so now the secondary oocyte is called this the ovum and then of course the smallest uh second polar body is also generated in this process so then what happens is that um the male and the female nuclei will then swell to form something called a pro nuclei which is explained i think on the next slide so what is fertilization again this is when uh the the membranes of the two-prone nuclei when they when they rupture this is the nuclear membranes when they rupture and the chromosomes from the male and the female they fuse together they combine together that's what we call fertilization so let's kind of explain this process so what you're seeing here is basically um the male and the female pro nuclei kind of swelling and as they approach each other the nuclear membrane of each of these nuclei they rupture allowing those chromosomes from the male 23 and the 23 from the female to basically come into contact with each other and as soon as that happens fusion when that occurs when the chromosomes of the male the female pro-nuclear intermix that's when we say fertilization has been accomplished this very first cell is now called the cyclot so which then prepares the zygote for the next main event that needs to occur and this is called cleavage which is basically um a rapid succession of a series of mitotic events okay so what is cleavage again like i said this is just mitotic divisions of the zygote are transforming it um from a zygote to basically um two daughter cells called blastomeres and then that ultimately those two cells become four cells four becomes eight it becomes 16 at this stage where you have at least 16 cells and that's called a morela so the very first cleavage division occurs at about 36 hours by the time you form this structure called the morula it's about 72 hours and then a little later on the more continues rapidly dividing or mitosis occurs resulting in something called a blastocyst uh where really you have about a hundred cells or so inside the blastocyst this is the structure that actually reaches the uterus so therefore from the time of fertilization as it goes through all of these cleavage events it could take about four to five days for that fertilized ovum that blastocyst to actually reach to go through the entire uterine tube and reach the opening of the uterus the the isthmus at this point the blastocyst consists of a very unique structure it's a kind fluid-filled a structure where you have an outer layer of cells called the trophoblast cells and then a population of cells on the inside called the the inner cell mass this is really important for you to know um i'm going to show you a picture identifying the trophoblast cells and the inner cell mass now what do each of these so what we really need to be focusing on from here on out is to talk about the transformation that's occurring uh these are this is all early embryonic development all these uh changes that need to occur keeping in mind what happens to the trophoblast cells ultimately this is going to result in the plus center and then the inner cell mass will become a bi-layered embryonic disc which basically consists of two layers and then ultimately from there uh that embryonic disc will further differentiate into uh the three most important germ layers so we will describe this process so um let's look at this schematic so you have a cross-section of the ovary shown here and of course that's the uterus the cervix leading at the vaginal canal kind of below here so um during the ovarian cycle the very first 14 days if you go with again a textbook cycle of 28 days the first 14 days or so is important in follicular development and we talked about all of this the development from primordial to primary to secondary and to this very early vesicular follicle and now you got a very mature vesicular follicle or an antral follicle shown over here then in response to lh that was released by the anterior pituitary it results in this ovulation event where the secondary oocyte remember this is arrested in metaphase two the secondary oocyte is ejected from the ovary um it is kind of propelled via these electrical kind of currents uh past these finger-like structures called the fimrae and then makes its way into the uterine tube so that's what you see in here a secondary oocyte that has been ovulated and then this next um stage here is showing you if you kind of uh zoom in a little bit more it's kind of showing you uh the approach of those sperm cells um onto the um secondary oversight of course um the acrosomal reaction needs to occur uh and then this is kind of showing you how those are pro nuclei fertilization is occurring uh the pro nuclei the nuclear membranes have dissolved now you've got fusion of the male and the female chromosomes resulting in the very first cell here called the zygote this is a fertilized ovum you can kind of see the zona pellucida are still intact now all of the the rest of these events that you see here are all cleavage events um as you go from this single cell to basically two cells and then you've got the four cells over here the four cells resulting in eight and then finally you've got the the morula right here which is basically a solid sphere of at least 16 cells at this stage this is that about 72 hours or three days this modular consists of a densely packed arrangement of cells here all of these cells are called blastomeres and at this point okay so you've got uh the movement of this um this ovum this fertilizer ovum as it makes its way through all of these cleavage events by the time you reach the estimus right here now this is called a a blastocyst this is about four to five days after um ovulation and after uh fertilization has occurred the blastocyst consists of well you still have the zona pellucida but it's almost disintegrating at this point this is where you rearrange this solid sphere of cells into an outer layer of cells which is called the trophoblast and then this inner cell mass right here this is a fluid filled cavity called the blastocyst cavity and at this point you're seeing that the zona placida is completely gone and you're just left with the trophoblast cells remember the trophoblast will ultimately um reorganize to form a very important structure called the placenta and then kind of hollows out to form this inner population of cells called the inner cell mass and of course you've got the fluid filled cavity so now what happens this is um the blastocyst that's going to kind of bounce back and forth for the next couple of days or so and if you if you remember the the wall of the uterus consists of an inner layer this lighter layer is the endometrium and then this is the muscle layer the smooth muscle the myometrium and then the outer layer here is the perimetrium so the blaster says this is about day four or five or so after fertilization it's going to take a couple of days to find a nice um hospitable uh spot um a nice home uh for this next event which is implantation so as you can see here this blastocyst this structure right here starts to invade into the endometrium kind of burrowing its way deeper and deeper into the endometrium this is a very important event implantation the earliest that implantation would occur is probably about six to seven days post fertilization but it takes about four or five more days to actually complete fertilization so you would say by about um day 11 or 12 or so after fertilization that's when implantation would be complete so if you're going with the ovarian cycle if uh if ovulation occurred at day 14 and fertilization remember the the the window at during which the the egg or the ovum is the oocyte i'm sorry is uh fertile or viable is only about 12 to 24 hours so if you go from ovulation to fertilization and all of this journey and for this implantation to occur which is about 12 days or so post ovulation and and fertilization that would be about day 26 or so so again if you kind of look back into the ovary remember the changes that were occurring here after ovulation the rest of the structure became transformed into the corpus luteum so the corpus luteum starts to produce progesterone and of course maintains levels of estrogen the corpus luteum is looking for this very critical event implantation it is asking the question if fertilization has occurred if we have a viable pregnancy in the fact that implantation has actually occurred because once this implantation starts to occur uh then this uh blastocyst this implanted blastocyst starts to produce hcg human chorionic gonadotropin which we talked about with the female reproductive system so the corpus luteum in the uterus is looking for increasing hcg levels uh which can only occur uh because of a successful implantation event so if the corpus luteum detects increasing hcg levels we know that we have a viable pregnancy and so therefore the corpus luteum remains viable for the next three months um sustaining this pregnancy or for the next two months uh if you're going to go from the implantation event sustaining this pregnancy um during which time almost as soon as the implantation starts to occur another very important process is occurring uh transformation is occurring here in the trophoblast i'll talk about this um resulting in the formation of a structure called the placenta now the placenta will take over from the corpus luteum takes about two months or so for the placenta to completely develop and become fully functional so about month three or so during the pregnancy um the placenta completely takes over at which point the corpus luteum is no longer required and it transforms into basically scar tissue okay so let's uh pick back up from here and continue on with this journey of what happens to the trophoblast cells what happens to the inner cell mass as we see this implantation event occurring okay so i i kind of already explained quite a bit of this uh so like i said the implantation can begin all the way from about day six or seven or so after ovulation and this is really an inflammatory event that's occurring um in the endometrium because if you think about it the the the blastocyst has to kind of uh kind of uh um push its way through the endometrium or borrow its way through and therefore this kind of sets the stage for an inflammatory even that allows that uh implantation to occur now the trophoblast let me back up you remember this outer layer of cells that i talked about called the trophoblast as soon as this implantation starts to occur it quickly differentiates into two separate layers uh the outer layer is what we kind of call the the the sensation trophoblast and this is the layer that actually starts to invade deeper and deeper into the endometrium and digests it as it pushes the blastocyst firmly into the endometrium and then you have another layer called the cytotrophoblast which is kind of like your inner layer so we'll talk about this um i'll show you a picture here in just a little bit um like i mentioned even though implantation begins around six to seven days uh post ovulation really it takes a couple more days to really complete this process and so implantation typically is completed by about day 12 after ovulation so kind of to show you what i was talking about on um in just a while ago if ovulation occurs at about day 14 if you count 12 more days post ovulation that puts you at about day 26 or so okay so this is really when um as ovulation i'm sorry as the implantation is occurring the um the implanting um blastocyst starts to release hcg human chorionic gonadotropin and like i mentioned on the previous slide the corpus luteum within the ovary is looking for these increasing levels of hcg and that's what's important to sustain this pregnancy and prevent degeneration of the corpus luteum so therefore as hcg levels are to increase and as they are sustained at about day 26 or so if there is a viable pregnancy by um these increasing levels of hcg the corpus lithium stays alive and continues on maintaining this pregnancy okay so kind of sorry let me back up here right quick i just want to show you i'm going to show you these two layers okay so the trophoblast becomes these two specialized layers so if you're kind of looking at it here uh this is the implanting blastocyst remember that was a cavity filled with fluid here's the inner cell mass so this is the trophoblast layer that's kind of making its way through the endometrium this being the endometrium up here um this this layer of cells or this population of cells becomes very aggressive and transforms into this region here called the sincerior tropogloss it's very very um aggressive like i said and starts to push its way and digest its way through the endometrium leaving behind another kind of a specialized population of cells here called the cytotrophic blast so the rest of it really becomes a cytotrophic blast so we're going to follow on with the journey of what really happens in terms of the sin city atrophoglass how does it actually help with the invasion process and then what happens to the cytotrophic blood cells and remember this mass where it was called the inner cell mass the cytotrophic glass is going to differentiate into your um violated embryonic um well partly becomes the the embryonic uh disc and then we're going to talk about the inner cell mass actually becoming the the actual embryo are resulting in all the organs of the first the three germ layers which then differentiate into all the different organs that are important for uh the embryo so let's kind of follow along with what's going on here with the changes occurring here as well as within um the inner cell mass okay um here's a schematic before i go any further here's a schematic showing you hcg levels um so okay so what do i have here the x-axis talks about the number of weeks uh gestational period um and then this is the blood levels related to different hormones okay so my my orange tracing is hcg levels green is going to be progesterone and blue is going to be the estrogen so you're starting from um the beginning of the ovarian cycle right there so ovulation occurring at day 14 a fertilization occurs then as implantation begins you're going to start to see that orange curve start to increase so this is uh what we call uh well this is the most important pregnancy marker that is really detected on a home pregnancy uh urine kit so and of course you can do this in the clinic as well using a blood test looking for these hcg levels so like i mentioned those hcg levels as they start to rise um as you detect this on a pregnancy kit um this is important because those levels of increasing levels of hcg determines the viability of the corpus luteum allows it to uh to stay intact and and therefore you're going to see an increasing level of progesterone and estrogen also starting to rise uh in relation to the hcg now the hcg levels will continue to rise tremendously and reaches its highest peak here about week eight so that's uh about two months into the pregnancy at this point um the hcg levels start to drop back down because if you remember this is right about the time when the corpuscle luteum hands over control to a fully developed placenta and since the corpus luteum is no longer required as those hcg levels start to drop the corpus luteum disintegrates and gets transformed into the corpus albicans or the scar tissue so if you're looking at this at about the fourth month or so into the pregnancy those hcg levels really uh come back to almost baseline levels um but what you're noticing here is that the progesterone in green and the estrogen in blue they are continuously sustained uh throughout the pregnancy so these levels are high throughout the pregnancy the progesterone is what we consider it has a calming effect on the uterus it prevents any kind of contractions of the myometrium you don't want any uh pre-term labor so the progesterone has a calming effect on the um on the pregnancy and and sustains a healthy pregnancy as you get towards the end here um the last couple of weeks right before um the delivery and the birth of the baby you're noticing uh progesterone levels start to start to decrease a little bit and a lot of other hormones kind of play a role in this process we have uh um [Music] oxytocin being released and then you've got changes occurring as well prolactin is starting to um get ramped up as well and prostaglandins are also released and and all of that will especially the the prostaglandins and the oxytocin will kind of antagonize these calming effects of the progesterone i'll talk about a little later on as well and that's going to really start to bring on those braxton hicks contractions like the false labor kind of preparing um mom for uh impending labor and delivery okay all right so let's uh let me back up here just want to show you all this is kind of where we stopped right we talked about the cytotrophic blast and then the um the inner cell mass i'm going to focus first on the sensitive trophoblast and kind of also go along along with the changes occurring here in this in the blastocyst okay so let's talk about placentation so this is where the trophoblast becomes uh forms the placenta uh the placenta is really important it's it's like like a bridge uh between uh the developing embryo and of course the maternal side of things uh because the embryo is not capable of um um breathing on its own so do so build up of carbon dioxide needs to be released through the placenta and it's basically taken care of by mom likewise delivery of oxygen and nutrients that is occurring from the mom through the placenta to the developing um embryo and then the fetus so we need to talk about how this placenta is formed it's a temporary organ it's only relevant throughout the life of the pregnancy and it really consists of the placenta consists of tissues from both the maternal side as well as the embryonic side so i'm going to discuss this and then of course the development of um i'm going to talk about the interval of spaces and then the chorionic villi the chorion and then of course the transformation occurring in the inner cell mass so let's kind of follow through with this so like to to to make sure you understand where we are um in relation to the uterus this is the the endometrium of the uterus okay so all of this pink pinkish kind of layer and of course the white part here is the lumen of the uterus so what you're seeing here let's start with the left this is the blastocyst that is pushing its way through the endometrium um kind of implantation is occurring here and so you're looking at the trophoblast becoming this uh very invasive proliferative synthetic trophoblast and then the rest of the trophoblast forming this layer here which is called the cytotrophic blast and here's the blastocyst cavity right okay so now i want to show you what's happening with the sensitive trophoblast and how it forms all of these changes you're going to have to follow through with the colors the sensitive trophoblast kind of shown in brown i want to show you the transformation kind of showing you all of the changes occurring here um allowing for the actual um kind of formation of the placenta and then i want to talk about what's going on here with the inner cell mass the inner cell mass transforms into uh basically a double a two layered kind of a structure called uh the embryonic the bilayered embryonic disc so um the nsl mass becomes this uh a specialized two layered structure called the embryonic disc and if you kind of look here this top layer in blue is called the epiblast and this uh lower layer in yellow or yellowish brown is called the hypoblast so that's a double layered kind of structure so the inner cell mass transforms into this embryonic disc and then i'm going to take it one step further here a little later on and show you how the the the bilayered embryonic this becomes the three most important germ layers and this process is really called gastrulation so i'll come to what's going on here on the center in a little bit i want to show you what's going on first with the sensitive trophoblast okay so here are the maternal blood vessels so as um this implantation event is occurring the maternal blood vessels there's going to be more and more blood vessels invading into this region right here the synthetic trophoblast starts to form these spaces these spaces ultimately get invaded by the the maternal blood supply as you can see here the maternal blood supply starts to fill into those spaces those spaces are called intervalus spaces or just lacunae or placental lacunae um and so you're seeing the blood the maternal blood vessels and the blood filling those intervals spaces now at the same time um um you're gonna see uh a reorganization of uh on the of these structures right here and these are called the chorionic bili so the chorionic bili is kind of associated with uh uh the embryonic side and then of course the interval of spaces kind of kind of flooding in here allowing for the maternal blood supply to kind of interact with the with the placenta now notice even even at this point you can clearly see that the maternal blood supply is not in direct contact with the the chorionic villian this is important because you don't want mixing of maternal and embryonic blood so this is really transfer of nutrients and waste materials that needs to occur back and forth is only through a process of diffusion it's not direct contact of the maternal and the fetal blood supply so all of that is kind of starting to happen here um as the sensitive trophoblast invades deeper and deeper uh and you're starting to form the interval of spaces and the chorionic the light now let's kind of look back on what's going on on the inside here so you have this bio-layered embryonic disc being formed and then also the very first part of the the like the amnion being formed which is separated from this bilayered disc by the amniotic cavity so this is going to really start to form the outer um kind of the sac like region which allows for um the formation of the or the development of the embryo and then the fetus within this um amniotic cavity so let's kind of look at these two layers which is your embryonic disc consisting like i said of this top layer which is the epiblast and the layer on the bottom here which is the hyperblast now if you're looking at the rest of this cytotrophic glass cells and kind of red notice how they start to differentiate and starts to form what we call the chorion um there's also other uh extra embryonic structures being formed ultimately if you kind of look at this transformation here from seven and a half days to about 16 days uh this allows for the transformation of basically forming an extra embryonic structure called the the yolk sac and the allen twas which is basically uh the base of the umbilical cord now this is this is really important the epiblast and the hyperblast which is your bi-layered embryonic disc at this point transforms into from those two layers it transforms into three germ layers and this is what we called um gastrulation those three germ layers in blue now that upper layer is called the ectoderm the middle layer in red is called the mesoderm and the lower layer in yellow is called the endoderm these three germ layers gives rise to all the organs and basically gives rise to the development of the entire embryo okay all right so i'm gonna i'm gonna continue on with my discussion of how this placenta continues to form and also track the changes occurring here with the development of the embryo okay so placentation is really like i said the formation of the placenta i'm going to show you all of these different layers um it takes about two months or so from the time of implantation to to really complete its formation and then of course become functional what are the functions of the placenta well of course to provide to provide nutrients to provide oxygen and to also get rid of the co2 that's building up in the uh in the embryo um excretory function so the the kidneys are not functional the lungs are not functional in the developing embryo so you have to be able to get rid of all of the co2 um you need to be able to get rid of buildup of nitrogenous base endocrine functions all of that hormonal regulation all of that is basically controlled through the placenta and basically mom is controlling all of that in relation to the developing embryo okay several different hormones are released by the placenta a little later on we'll we'll talk about some of this relaxin um human placental lactogen and of course uh human chorionic thyroid okay so this is a little further along this is about a four and a half week embryo if you're looking at this the placenta is really starting to take shape i just can't kind of go back to what we were discussing this is all the the the maternal artery um and then the maternal blood vessels they are all of the blood vessels kind of invading into um i'm kind of forming the placenta uh pooling of blood that you see here in the interior spaces on the uh embryonic side of things you're starting to see a nice network of formation of those chorionic villi right there again you can notice that it's not direct connection or direct mixing of the maternal and the embryonic blood okay this is just literally in close proximity or in the vicinity but not in direct contact now what you see going on here on the inside you see a very nicely formed amnion here with the amniotic cavity uh and of course uh let me back up here you remember those three germ layers we talked about the ectoderm the mesoderm and the endoderm well that's actually going to start to form all the different organs and that you see in this developing embryo right here now the embryo is like i said kind of isolated in its own little cavity this is the amnion and the amniotic can be filled with amniotic fluid and then we remember we talked about the yolk site just a while ago and then this would be uh basically the uh the developing um umbilical cord um the chorion um which is the embryonic uh part of the placenta uh and the deciduous basalis which is uh part of the the endometrium but this would obviously be the the maternal side of the placenta so really the placenta just want to point out i think i had this here right here the placenta consists of like i said maternal tissue as well as the embryonic or fetal tissues um the maternal portion of the placenta is what i called the decidio basalis um and the fetal portion or the embryonic portion is called the chorionic vely so the two together really kind of make up uh like the entire placenta and it requires uh it requires both maternal and fetal tissues to form that connection or that bridge okay okay um now if you kind of take it even further this is a 13-week fetus this is at the end of the first trimester you're seeing that the placenta is very well developed and kind of uh concise and all of the structures that we just talked about they still are relevant you can see the developing embryo here well at this point remember this is uh this is past week eight from week nine onwards you don't call it the embryo you call it the fetus so this is a developing fetus within uh this blue layer which is the amnion this entire region is the amniotic cavity filled with fluid like i said a yolk sac right there a nice a well-formed umbilical cord which allows for that connection right there between the developing fetus and the placenta right there okay um so what i want to do next is to talk a little bit more about kind of zoom in on this region here this is a fully formed placenta percentage is completely functional allowing for uh movement of say oxygen and nutrients from the maternal blood supply through the umbilical cord into this fetus and then the removal of waste products back through this entire arrangement to where mom is able to uh remove those uh base products through uh the maternal venous site okay so i'm gonna zoom in a little bit on this region to show the the movement of materials on the arterial side as well as the the venous side um so um hcg and of course the placental hormones that need to be uh adequate because um okay so if the placenta is not able to do its job then that would be a reason for aborting the pregnancy um so um high levels of estrogen and progesterone is really important for all of these processes to occur and to continue with a successful uh pregnancy like i already mentioned um maternal and embryonic or fetal blood supplies are separate they don't directly intermix uh so let's talk about kind of kind of zooming in on this region okay so i'm going to show you what's going on here this is uh the endometrium um well this would kind of be the myometrium and you can kind of see the endometrium right here so you're seeing uh portion of the placenta right here uh so if you're kind of following through on the maternal side um the red blood vessel will be the maternal arteries uh draining that blood into this space here called the interval of space here are the chorionic villi which is part of the placenta but on the embryonic or the fetal side um so if you're kind of following through let's kind of simplify it here for you uh nutrients oxygen uh carry through the maternal artery will diffuse into this space here the interval of space and then from here and there's no direct connection like i said between the chorionic villi and the interval space but the oxygen and the nutrients will diffuse across into the chorionic villi and then you're going to take all of that through the umbilical cord but inside the umbilical cord you've got three vessels so all of that good nutrients is carried through this red vessel this red vessel is called the umbilical vein if you remember way back we talked a little bit about how the nomenclature for arteries and veins is reversed in the case of the pulmonary circulation and in the case of the fetal circulation so this is a red vessel typically you would want to call it an artery but remember this is a this is a fetal blood vessel so therefore this is the umbilical vein carrying oxygenated blood uh to the developing fetus so i've got it written out here now bringing all of your um waste products out of the fetus remember it all has to cross through the placenta and it's taken care of by mom so you have two blood vessels here shown in blue a pair of umbilical arteries will carry all of the waste products again back into the chorionic villi and then from here that all of those waste products would diffuse back into the interval of space and then it's taken out through the um maternal veins okay so that's kind of shown here the differences between what's going on from the maternal side towards the the fetus and then from the fetus back towards the maternal side so just to reiterate the placenta really consists of a combination of tissues from both maternal as well as the fetal side the maternal portion of the placenta is what we call the dissidio basalis and the fetal portion of the placenta is basically all of the chorionic villi okay so i think we've covered um the whole idea of fertilization leading to implantation um the role of hcg and all of that and then we kind of went ahead and talked about how the placenta is formed uh so and what we need to next talk about is kind of backtrack a little bit uh if you kind of go back to what we were discussing just a while ago uh which is this process here is how does this um balayage embryonic disc how does it transform into this uh all three germ layers and this process is called gastrulation and then how do these three germ layers actually give rise to this developing um embryo or later on the fetus and all the different organs within this within this field so that's what we want to talk about next okay so um gastrulation so this is going from a two-layered embryonic disc where you had an epiblast and a hyperblast those two layers how do they get transformed into three main germ layers are called ectoderm mesoderm and endoderm uh this typically starts to occur during week three this process of going from an embryo like this to the three germ layers the formation of the three generally is called gastrulation okay this begins with a very important event uh called a primitive streak uh so you first need to establish uh the longitudinal axis like you know where where's the head going to be versus where's the bottom uh of the the feet kind of going to ultimately be so you want to kind of establish where's the top where's the bottom okay and so we're going to define something called a primitive straight and then all the different uh kind of the events i'm going to keep this as simplistic as possible i don't really need you to understand or kind of remember too many minor details with respect to the process but i want you to understand key terms okay so again bottom line is we're going from this embryonic disc to the three germ layers and so we're going to define this process so this was the invading sensitive trophoblast and starting to form that interval of spaces and all of that but again this is the cytotrophoblast and then the inner cell mass if you remember it started to differentiate into you had a billiard embryonic disc here the blue layer follow through with the colors that's going to be relevant um the blue layer is the epiblast and then the yellow layer we call that the hyperblast and of course this is the amnion with the amino acid it can't be starting to form so we're going to we're going to take these two layers and transform them into these three layers okay this is the process of gastrulation if you're going to zoom in a little bit on this region i'm going to show you what's going on here again the top layer in blue is the epiplast and the layer on the bottom is the hypoblast so right here on the dorsal aspect of this epiblast you kind of form a groove and this is what we call the primitive streak the epiblast cells start to cave inwards as you can kind of follow those arrows it starts to cave inwards towards this groove and then it's going to push downwards and out as you can see here this transforms this upper layer into now what we're going to call it uh the ectoderm and then this deepest layer the hypoblast really transforms into the endoderm and then the population of cells that ends up in between here as shown in red is the mesoderm so this is the transformation of the uh the bi-layered um embryonic disc into your three germ layers namely your your top layer here the ectoderm uh the middle layer in red which is your mesoderm and your your bottom layer here which is the endotherm now what do we do with these three germ layers when all the different organs of this developing um embryo and then the fetus of course all of those organs need to be derived from one of these three layers so i'm going to talk about that next okay so gas relation is the formation of those germ layers uh those three germ layers we call them the ectoderm the mesoderm and the endoderm so bottom line is ectopictos outside or outer uh the ectoderm becomes all of the the skin epidermis which is the outermost layer of the of the body right the epidermis of the integument and then all the nervous system is derived from the ectoderm so then what is the endoderm the endoderm is the innermost layer so therefore it becomes all the innermost lining of all of your digestive respiratory urogenital organs as well as the innermost lining of all of the glands so you think about this this is the the mucosa layer of all of the innermost organs of the body and everything in between is derived from the mesoderm so we're going to add a little bit more detail but as long as you understand this main concept the rest of it should be uh fairly straightforward so we're going to talk about okay so gas relation was the formation of those three layers then the formation of all of these different organs from these three germ layers is organogenesis okay so this occurs um from the time of gas relation so about week eight or so pretty much all the very primitive organ structures are somewhat recognizable uh we're going to talk about uh several different different events occurring here so let me back up remember we said the ectoderm becomes a nervous system this is one of the the first events that occurs in inorganogenesis the formation of the nervous system uh and kind of an event called new relations we'll talk about that right here so this is uh formation of your all of your nervous system uh structures uh remember the brain the spinal cord that we discussed in a np1 these are your central nervous system organs so how do you give rise to the brain in the spinal cord there's several different events that occur i'm going to describe them for you uh neural tube and then and so on and so forth then there's a population of cells called the neural crest cells which give rise to okay remember from the brain there were um pairs of cranial nerves that were generated so all of those cranial nerves and then the nerves from the spinal cord namely the spinal nerves all the sympathetic ganglia and all of that that we talked about uh all of this is derived from the neural crest cells the adrenal gland the medulla region which gives rise to the chromosome cells which give rise to the epinephrine and the norepinephrine during the sympathetic response well that also uh comes from the neural crest cells and the pigment cells of the skin also from the neural crest cells so this is basically the most important um concept one of the most important major events that occurs during organogenesis this is from that ectoderm layer ectoderm germ layer okay uh the mesoderm what happens to the the middle germ layer the mesoderm this becomes all of the different organs or the major organs of your body so we're going to define this as the semites um and i break the style of the sclera term the dermatome and the myotum and then there's an intermediate mesoderm that's also formed this uniform the gonads like the ovaries and the testes and the kidneys the lateral place plate mesoderm forms pretty much everything else the heart the blood vessels the respiratory organs the digestive organs all of your connective tissues pretty much everything is formed from the mesoderm the ectoderm forms the nervous system and the skin epidermis the endoderm forms the innermost linings the mucosa of all of your organ systems and the mesoderm pretty much forms everything else so let me show you the event uh kind of occurring with respect to new relation so if you're gonna if you look at um your three germ layers here right remember that blue layer on the top was the ectoderm uh all of the layer the cells here in the middle were shown here in orange is the mesoderm and then the innermost layer was your endoderm those were your three germ layers right how do i take these three germ layers and bring about organogenesis all the different organs that need to be formed in the developing fetus so the first event like i said that needs to occur first major event occurring um during organogenesis is this idea this concept called new relation so uh you see uh like a like a hot spot or a center being formed there um this is called the notochord um and the notochord causes thickening of the ectoderm layer right above it forming something called a neural plate the neural plate will then form a groove which then kind of forms a fold like this okay and forms a groove and then this groove ultimately closes in forming basically the neural tube okay um so this occurs like about um day 20 day 22 or so so once the neural tube is formed um the anterior aspect of that neural tube becomes the brain and then the rest of it as it pres as it continues downwards becomes the entire spinal cord okay here's a population of neural crest cells that are also formed as part of the new relation process remember these cells really i'm sorry form the cranial nerves the spinal nerves the adrenal medulla and so on and so forth okay now in the process also as new relation is occurring and as those changes are occurring within with the um nervous system you also see changes occurring here in the mesoderm right the mesoderm becomes three important regions you have the somite region the intermediate mesoderm region and the lateral plate mesoderm i'm just going to very briefly show you what goes on in those three different layers and then of course um we're going to also talk about what happens with the with the endoderm layer and how it forms innermost lining i think that's what yeah shown in this picture right here so the endoderm basically becomes so you have a very uh uh alien looking um embryo or the spinous is a five-way called embryo so you're starting to see that the the endoderm which is the inner most germ layer it starts to form the innermost lining of all of your internal organs all of the uh respiratory uh regions so like the pharynx uh the glands associated uh with the with a lot of these different regions a thyroid gland for example um then kind of starting to form the the trachea the lungs as you can see here which are all like your respiratory organs then the the the tube right behind the trachea which should be the the food food pipe the esophagus the innermost lining of the stomach which is baked so all of this is the g the gi tract um the most rudimentary versions of the the small and the large intestine and the lining of the the liver the pancreas all of your um [Music] major glands so all the innermost the mucosa the epithelial lining of the gi tract the respiratory tract and the associated glands are all formed from the endoderm i'm just going to back up a little bit i want to i want to go in a little bit more detail here with respect to the mesoderm uh what happens to the so my the intermediate mesoderm and the lateral plate mesoderm so this schematic is really important because this really puts into perspective um the three germ layers right the ectoderm uh the mesoderm and the endoderm and all the different structures that are formed uh from these uh struck from these three germ layers so like i said the ectoderm becomes a skin epidermis all the appendages related to the skin so the hair nails all about the glands of the skin and we talked about the formation of all the nervous system structures so like the brain the spinal cord the nerves the glenglier the adrenal modular all of that is coming from the ectoderm with the inner muscle the endoderm the endoderm like i said was the epithelial lining of all of the glands the digestive structures the respiratory tract all of that so what's the mesa i'm gonna do everything in between right so that's the middle layer i want to show you here how the mesoderm forms uh the somate the intermediate mesoderm and the lateral plate nicotine what are the somites the somites then form three different divisions or regions the sclerotome gives rise to all of the ribs and the vertebrae the dermatome gives rise to the dermis region and then the maya term is all the muscles the skeletal muscles the intermediate mesoderm gives rise to the kidneys and the gonads the ovaries and the testes um and then the lateral plate mesoderm gives rise to pretty much everything else which is the heart the blood vessels all the connective tissues um the wall of the respiratory respiratory tract digestive tracts all of that okay so make sure you um know the derivatives of the ectoderm the mesoderm and the endoderm okay so um i think we've talked about most of the developmental aspects of the early developmental aspects of embryonic development so what we need to talk about next is a little bit about fetal circulation which most of this was covered in lab i just want to do a quick recap and then move on to talk about changes occurring uh during fetal development uh remember um fertilization to week eight is the developing conceptus is called the embryo week nine up to birth is called a fetus okay so uh what are some of the circulatory changes that are occurring in the fetus one of the first organ system that's that's actually uh kind of developing the fastest during fetal development or during embryonic development is uh the cardiovascular system in fact there's a heartbeat that's that can be detected as early as three and a half weeks uh in a developing embryo and remember [Music] in terms of the fetal circulation you had an umbilical vein that carries oxygenated blood and then a pair of umbilical arteries that carries oxygen poor blood through the placenta back to the maternal side of the blood circulation three important vascular shrines that we need to talk about in the case of fetal circulation the ductus venosus this is the one that bypasses the liver the ductus arteriosus this bypasses the pulmonary trunk basically connecting it directly to the aorta i'll show it to you and then the foramen bali this is actually in the interatrial septum between the left and the right atrium and this is another method to bypass the pulmonary circulation bottom line is this now developing embryo or a fetus um the the liver is not functional okay so therefore we want to deliver the least amount of blood to the to the liver to promote or to sustain its development but not really because it's not functional you want to bypass most of the blood um to the rest of the feet the rest of the fetus and that's where this shunt comes into play and also the lungs are not functional so um if you think back to the cardiovascular system you want to basically prevent too much of the blood actually going into the lungs because that's not really responsible for elimination of carbon dioxide there's no respiratory function so there's two important shunts which uh facilitate bypassing the pulmonary circulation uh the foramina valley and the ductus arteriosus so let's look at this picture right here so this is the placenta here on the bottom okay so this is um kind of showing you the developing fetus right here you see the feet the fetal lungs the heart of course the kidneys and the the liver and so we're going to show you um where those shunts are located and what are those important blood vessels let me kind of back up want to identify all of this in this schematic right here so um all of the you would imagine here on the bottom you've got the maternal side right the maternal blood supply and everything so all of that oxygen rich blood from the maternal side right will then enter through the placenta it's delivered through this dark red vessel this dark red vessel corresponding to high oxygenation this dark red vessel is basically the umbilical vein okay so the umbilical vein and this this is the umbilical cord so the umbilical cord consisting of the umbilical vein and the two lighter vessels which are your umbilical arteries so oxygenated blood is going to lead through the umbilical cord and through this vessel here which is the umbilical vein here's the umbilicus as you can see so here's the umbilical vein okay the very first thing is i want to point out you're going to see mixing of oxygen rich in oxygen poor blood uh within the fetus which obviously does not occur um in a normal human being after birth uh but this is a very unique circulation pattern in the case of the fetus you're going to see many different regions where there is mixing of of blood so every time you see purple and that's typically where you see a mixed load of both arterial and venous load so that oxygen rich blood the first thing is it's taken to the liver um and since the some some of that blood is is uh delivered to the liver but most of it is shunted um through this shunt right here and this is what we call the ductus menosis most of it is um kind of bypass bypassing the liver and takes it directly to the inferior vena cava as shown by this blue vessel now if you remember the circulatory pattern the inferior vena cava and superior vena cava that's going to allow for blood to enter into the right atrium right there right and then from here typically it should go through this valve right here uh into the uh right ventricle right so because and then if you remember from here it's taken through the pulmonary trunk to the to the lungs but because the lungs are not functional uh here's your second bypass this is gonna bypass the pulmonary circulation uh so there's actually an opening here in the wall the interatrial septum between the left and the right atrium which allows the blood to immediately be diverted directly here to the left atrium and then from there it's transported out through the aorta where it can be circulated to all the different organs of the of the developing feeders so that's one shunt to bypass the lungs the second shunt is this some of the blood actually does enter into the right um ventricle and then from there it's gonna go through the pulmonary trunk but here's your second shunt instead of allowing that blood to actually enter into through the pulmonary arteries into the um the lungs there's a shunt right here uh and this shunt basically takes the blood from the pulmonary trunk directly into the aorta so that that shunt is now again a bypass for the pulmonary circulation and this shunt is called the ductus arteriosus okay uh so all of the oxygen poor blood returning from the different organs of the developing fetus they return through these two uh lighter reddish kind of blood vessels um these are called the umbilical arteries and then of course when you return that back to the placenta and then on to the maternal side of things so pay attention to everything here in red okay um so the umbilical arteries the umbilical vein the the liver shunt here the ductus arteria i'm sorry the doctor's aminosis um the opening in the interatrial septum which is a foramina valley and then of course the pulmonary shunt here which is the ductus arteriosus everything in red is um the modifications that you see in the in the fetal circulation but immediately after birth okay where the liver becomes functional the you the baby takes its first breath and so therefore the lungs become functional then all of these accommodations that were specific to the uh the fetus that you see here in red need to convert to what you're seeing here in blue so this is in um fetal uh circulation and this is in a newborn after birth where you wanna where you have to um kind of um reformat the circulatory pathway right and so after the umbilical cord is is cut um the placenta is no longer functional that's why you don't see a placenta right here right now the baby has the newborn has to um basically do a lot of uh a lot of the work that mom was doing for it um prior to that the baby needs to be able to do by itself so the liver becomes has to become functional um waste products have to be removed by the by the kidneys by the lungs in terms of the co2 elimination and of course you want to reroute that blood to uh to to what you typically know the cardiovascular pathway to be so um let's look at this um that umbilical the umbilical vein um becomes a ligament called the ligamentum teres and those two umbilical arteries are no longer required so they become the medial umbilical ligaments this shunt here which was the the liver shunt the ductus venosus well you don't need to shunt it anymore you need you need all of that remember the hepatic portal circulation all of that blood needs to go through the liver for detoxification for looking for pathogens those macrophages need to be able to do their job and remove those pathogens so again we want one all the blood routed through the liver so therefore the ductus meiosis and goes away basically it becomes a ligamentum being awesome so this is these are just ligaments okay now that opening here uh in the wall of the the i'm sorry the interatrial septum between the two uh atria that starts to close up becoming uh literally uh like a depression in the entire atrial septum called the fossa obvious the shunt here between the pulmonary trunk that shunted blood directly into the aorta bypassing the lungs uh no longer exists that needs to also close back up becoming the ligamentum arteriosum i'll talk about this a little later on uh all of the ligaments um most of them they typically they they they get transformed pretty quickly uh like a few minutes or so after um the newborn um is delivered uh the um the foreign takes a little longer it could take a few months maybe even up to a year after birth to fully close back up you know this comes up a little later on in our discussion as well okay so now i'm going to quickly go over all of the changes that are occurring in fetal development remember this is period from between nine weeks all the way to the birth of the baby so i want to very quickly highlight certain changes occurring in the developing fetus not going into too much detail though so so this is basically at the end of eight weeks so starting week nine all the way to birth so that's the fetal period so at the end of eight weeks you're seeing that uh we've got a developing uh almost an alien looking um fetus right here the head and the body are very disproportionate to each other the head is almost as large as the body um all of the different like brain development is occurring brain regions are starting to be formed of course this is really when um ossification of the formation of bones start to occur we talked about this in a mp1 endochondral and um intra membranous ossification needs to occur uh the only organ system that's fully functional at this point remember there's a fully functioning heart and heartbeat can be detected as early as three and a half to four weeks so by this time at eight weeks you have a fully functional cardiovascular system uh moving a little further on month three or so so this is 12 weeks head is still fairly large but kind of becoming more proportionate with the rest of the body the skin epidermis and the dermis is uh is formed uh rather the eye is is formed uh you're going to see more development of the spinal cord the cervical and the lumbar enlargements blood cell formation all of the hematopoietic stem cells forming the different lineages of blood cells that's all starting to happen uh in the bone marrow um at this point sex uh male versus female genitalia can be very easily identified and this is again end of the third month fourth month okay so this is really where a lot of the sensory organs are starting to differentiate and develop blinking of eyes sucking motions uh all of that is visible um in an ultrasound okay the face is starting to look a little bit more human and starting to become a little bit more the head is becoming more proportionate to the rest of the body meconium is starting to collect in the gi tract which is basically waste material that will be released after the newborn is formed can also start to be released [Music] later on in the pregnancy as well at at five months uh wernick's caseyosa is uh is being secreted this is basically the sebaceous glands uh resulting uh releasing a fatty secretion there's also very very very fine hair like um structures called lanuga covering the skin at this point um at about month five there's not much room in in the for the fetus in the divi in the uterus as it kind of stuck as as it swells so the baby assumes a fetal position quickening very exciting month for mom mom's able to feel those spontaneous movements of the fetus so this is what we call quickening um one six and seven a lot of different things happening here mostly um [Music] substantial increase in weight uh body temperature is still not very easily regulated the hypothalamus is starting to regulate body temperature and then the lungs are starting to produce surfactant but none of this is still adequate at this point uh myelination forming of those myelin sheaths uh in those axon processes of neurons is is is occurring here the eyes can be open at this point um in the case of the male this is when you see a descent of the testes into the skranam this last couple of months uh last 10 weeks or so is really when most of the fat depositions occurring in the hypodermis of the of the skin so this is in the subcutaneous tissue so that kind of wraps up the main developments or the main changes occurring in the fetus um all the way from week nine to the time of birth okay here are some of the changes that are occurring in mom we'll talk about anatomical changes and then of course metabolic changes as well uh so anatomically okay well of course you're gonna start to see breast enlargement um you're gonna see pigmentation kind of uh differences occurring especially the areola uh in the breast tissue starting to darken the uterus will start to uh expand um ribs will start to flare out uh lower doses so this is where the uh swelling uterus uh causes um [Music] a curvature in the in the lumbar region of this of the uh were kind of like an abnormal curvature in the lumbar region this is called lordosis to to kind of compensate for a change in the center of gravity relaxing is very important this is being released this is gonna allow for um kind of uh expansion of the pelvic area um and up the pubics and pieces between the two coxal bones to allow for again widening of the pelvic space to allow for easier passage of the baby during labor and delivery should um should a vaginal delivery occur anatomically a lot of different changes occurring if you look at the the size of the uh uterus about the size of a fist um early on like prior to uh conception and then you notice how there's a dramatic changes occurring and but we're looking at um about let's say the seven months this is really where the fundus of the uterus is well above the umbilicus and then as you um get to the end of the pregnancy it's all it's pushing up on the xiphoid process which obviously can make um heartburn an issue can also cause uh difficulty with breathing uh kind of getting very um large and the entire the of course fetal position is already assumed uh much earlier on so in terms of nutritional goals you want to add about 300 or so additional calories they have to have nutritional value not necessarily any calories but anything with anything that enhances vitamin content and of course folic acid that's going to be really important in terms of nutritional value for a pregnant female folic acid is going to reduce the risk risk of many neurological problems like spina bifida and of course it's going to reduce also the occurrence of spontaneous preterm birth several different uh hormones being released by the by the placenta human placental lactogen is one of them we'll talk a little bit about this as we uh uh discuss this in relation to um lactation and and things like that as we get close to the end of the pregnancy physiological changes many different changes occurring in mom or as as she goes through the pregnancy there okay let's start with uh let's say the gi tract okay so elevated levels of hcg is going to cause uh that classic morning sickness that a lot of females experience um this is also due to elevated levels of estrogen and progesterone which of course can cause um other other gi tract problems like of course heartburn and constipation um especially as the uterus starts to uh expand uh well a lot of the other intestinal organs like the small large intestine they get cramped which can really cause constipation issues as a result as a result of poor motility of the food as it passes through the gi tract um elevated levels of the uh any of these hormones can also kind of cause heartburn of course this is uh later on as we go towards the end of the pregnancy pushing up against the xiphoid process that can also cause problems with respiration can cause dyspnea which is difficulty breathing that can occur our tidal volume increases very very dramatically throughout the pregnancy edema and congestion that is experienced by some females is because of increasing levels of estrogen now one of the most profound changes that occurs during pregnancy in a female is the changes occurring with the cardiovascular system so blood volume can increase this is pretty dramatic up to about 40 or so cardiac output also increases 35 to 40 so therefore there's a there's a lot more blood being circulated throughout the body of course this is to also allow for um delivery of nutrients to the development fetus through the placenta but of course as cardiac output increases venous return would also have to increase and and the weight of the developing uh uterus or the expanding uterus uh applies puts a lot of pressure on the lower the veins of of the lower extremities so resulting in varicose veins which is where you have leaky valves uh makes it much harder to return that blood back to the uh the right atrium um and then of course uh in car in relation to increases in blood volume you're also going to see increases in urine output uh and to compensate or to to kind of adapt for increased maternal metabolism and of course elimination of those fetal bases well of course as um the uterus expands that's going to uh kind of push up on push up against the bladder making it harder to store urine in the bladder for um for long periods of time therefore you see more frequent urination sometimes even incontinence problems that occur especially towards the end of the pregnancy okay uh one homostatic imbalance related to pregnancy is preeclampsia which is basically um where you have problems with uh with the blood supply through the through the placenta and therefore the fetus can get starved with nutrients and and oxygen supply so that can be a problem um so now that we talked about all of the changes occurring in the fetus and of course changes occurring in the in pregnant mom as she goes through the pregnancy uh the last few concepts i want to discuss is as we get to the end of the pregnancy what are some of the changes happening how does the female body prepare for labor and delivery what are some of the hormonal regulatory features that actually controls this process so labor is basically uh giving birth to the baby these are expelling the infant expelling the the fetus from the uterus um allowing for the birth of the baby a lot of this is actually uh caused by many different uh hormones but okay during the last few weeks of the pregnancy um the lungs is is really the the last organ to complete um maturation and becoming kind of starting to become functional and to prepare for to birth so the the lungs um within the alveoli the wall of the alveoli i have certain cells that produce surfactant protein and this is what this kind of helped keep the the air is open we talked about this with the respiratory system um so increased levels of spa that occurs during the final weeks right before delivery it kind of signals uh to the body okay uh to the uterus that it may be time to start making changes uh in preparation for uh labor and delivery so what some of the changes that occurs in the spa can prompt an inflammatory response in the cervix of the uterus causing it to to efface or to kind of soften and to kind of thin out um effacement which is an important aspect of preparing for labor some of the other things that are happening many different things really like i explained just a while ago a few slides ago i said progesterone is really important estrogen as well but progesterone is important in its calming effects very important to keep the developing fetus inside of the uterus and to prevent it from being expelled to prevent any pre-term labor progesterone is is an important hormone that sustains the health and the viability of a pregnancy but towards the end of the pregnancy uh as um let me back up i'm sorry um as the cervix starts to soften and then you've got changes occurring here um as all of that starts to occur then there are other hormones that are released like oxytocin oxytocin is uh being released um from the pituitary um which kind of serves as an antagonist it serves uh it serves to kind of ruffle up uh the progesterone so therefore it inhibits the calming effects of of progesterone and therefore kind of starts to induce labor contractions which of course will ramp up in intensity and duration as you go into full-blown labor uh allowing for the delivery of the baby so there's a few other things that are also occurring here uh braxton hits the when oxytocin levels start to increase and you start to antagonize the progesterone initially you see what we call false labor or kind of practice sessions leading up to actual true labor and so that braxton hicks contractions can occur less frequently and much less intense and then of course as all of these changes occur in the last few weeks of pregnancy you also start to see the fetus signaling that it's time for delivery of that of that baby and so feel oxygen starts to increase which then cooperates uh kind of produces these inflammatory chemicals called prostaglandins so the oxytocin and the prostaglandins together are very very important in promoting uh labor contractions or uterine uh contractions so by antagonizing progesterone okay so we'll talk a little bit about this um as labor progresses as you go into full-blown labor uh the intensity of the contractions becomes much stronger and they also come closer together and that is true labor and during this entire process where contractions are occurring the myometrium of the the smooth muscle of the uterus this is going to cause changes in the cervix as well causing it to basically distend kind of thinning it out we'll talk about effacement and also starts to open up the cervix um so that's called dilation and has more of the oxytocin and the prostaglandins are released that causes more changes to the cervix and so you have a positive feedback mechanism as the cell exchange is more that prompts more and more release of oxytocin and prostaglandins and so you have a feed forward kind of a cycle a positive feed for a feedback cycle that allows for progression of labor so let's kind of add a little bit more detail to this um and kind of then discuss the different stages of labor okay so okay so um estrogen levels uh start to increase um and this is going to promote kind of the the release of uh well it's going to prepare the uterus uh by upregulating the oxytocin receptors okay and as oxytocin gets released from the mom's uh posterior producer initially it's from the fetus but then later on it's also a cooperative effect of oxytocin being produced even from mom's pituitary so let's just say from both mom and fetus oxytocin is going to this is the stimulant that causes the myometrium of the uterus to contract so the smooth muscle starts to contract uh oxytocin also does one more thing it allows the placenta to release prostaglandins the two together the prostaglandins and the oxytocin together allows for stronger and stronger contractions of the uterus and you can see that this is a feed forward cycle as there's more prostaglandins that causes more oxytocin to be released and the two together causes stronger more vigorous more intense uh [Music] contractions uh occurring in the uterus okay okay so what are the different stages of labor um the dilation phase or the dilation stage is the longest stage of labor um this is a modest number of six to 12 hours kind of depends um this can this can depending on i guess which pregnancy so if it's if it's the first pregnancy this can this can actually be uh even longer than 12 hours or it can be a much faster process if if it is a second third or any kind of subsequent pregnancy because your your body is primed and has been through it once before so it's typically much easier and kind of faster um in a subsequent pregnancy in relation to the first pregnancy so what do i mean by dilation so this is where the cervix goes from a fully closed uh stage where it's zero centimeters to a fully dilated cervix this is ten centimeters going from zero to ten centimeters could take six to twelve hours typically and we're going to even further break this down into an early and a late dilation phase so during this during this stage let me back up remember the oxytocin and the prostaglandins are being released and what this does is this increases the contractions in the wall of the uterus right and so you basically have uh you know the contractions urinal contractions occurring as very weak contractions about 15 to 30 minutes apart and every time there's a contraction it's about 10 seconds or 10 to 30 seconds long but as more and more oxytocin more and more prostaglandins are are released oxytocin is going to ramp up these contractions and as this is occurring uh there's uh there's changes occurring and the head of the baby has is is starting to make uh contact you know with the cervix causing the pressure of the of the head pushing down the cervix causes the cervix to thin out and this is called effacement and then as it thins out it also starts to open up and this is dilation it opens up from zero to all the way fully dilated uh at 10 centimeters somewhere in this process during the dilation phase or during the during the dilation stage in most women the amniotic the amnion can rupture resulting in release of expulsion of the amniotic fluid which typically um again this could happen in in the late dilation phase uh sometimes in the early dilation phase and sometimes it does not happen uh and the the the obstetrician may have to actually rupture or break the amniotic sac by themselves so it kind of just really depends from pregnancy to pregnancy but typically this is what you expect to see all that pressure and all of that increased urine contractions and as the baby undergoes some changes in terms of its position and as it pushes down in the cervix this typically uh causes the amniotic fluid to to rupture engagement is really where we talk about the babies and the the fetus's head uh entering the the pelvic region and again causing a lot of those changes occurring in preparation for delivery of the of the infant so i want to talk about a few more things here um before i go into a schematic showing you the different stages again uh dilation that's the longest stage of labor expulsion is really where uh you go from fully dilated cervix to the delivery of the baby contractions are very strong at this point um coming every two three minutes apart typically and each contraction lasting about a minute probably even longer uh so to to where they are pretty intense where you don't really um get a chance to to kind of take a break between contractions and that's important is is to to maintain the intensity of the contractions to allow for this expulsion stage to actually occur and to be accomplished crowning crowning occurs when you see the largest diameter of the dimension of the of the head the the head of the fetus start to to distend the the vulva episiotomy may be required at this point uh to kind of reduce tearing um to allow for opening of that region now the baby can present in in different forms i guess uh positions and the head first is the head first presentation is called the vertex position this is um where the skull the as it pushes downwards it helps to complete the dilation of the cervix and also as the baby is delivered through the birth canal and this can allow for suctioning of the nasal passages to to suction out all of that amniotic fluid and to allow for to facilitate easier breathing when the baby is born now as opposed to the head coming out first if it was the the bottom then this is called the breach position this oftentimes is much more labor intensive much more difficult may require forceps for this and may even cause complications to the point of needing or requiring a c-section okay the last stage is the placental stage after the delivery of the baby after the birth of the newborn well then the delivery of the placenta and all the membranes also needs to happen and this is called delivery of the after birth which occurs during the placental stage so here are the three um three main phases the early dilation phase the late dilation phase and of course expulsion and placental stage uh dilation showing um the head of the fetus pushing down on the cervix causing it to um to thin out a placement and then starting to see dilation right there typically going from zero to six centimeters is considered early dilation um and then of course late dilation would be going from six to about to fully dilated which is 10 centimeters and this is again where you're going to see the baby's head rotating um kind of in the the anteroposterior axis where the the face kind of faces um the sacrum and the coccyx region kind of in that region there and then the this allows for the easiest delivery of the of the fetus as it goes through the vaginal or the birth canal once the cervix is fully dilated at 10 centimeters this is really where the you you see the the most intense um contractions and then of course resulting in the expulsion of the of the fetus now the expansion stage can be anywhere from [Music] 10 to 15 minutes um to maybe as long as 45 to 15 minutes maybe an hour but that's the expulsion phase where um the contractions are will help with the delivery of the of the of the entire fetus and then typically within about 30 minutes after the the baby is born on the delivery of the newborn has occurred then the placenta and all of the um other embryonic tissues will then need to be expelled as well and this is the delivery of the after birth which occurs during the placental stage okay just a few more uh concepts here before we wrap up this uh this chapter so after the infant is born uh there's um we go through a transitional period uh but the the most important thing that occurs within the first five minutes after the birth of the infant is that is uh assessing something called the apgar score uh this is based on five different parameters the heart rate respiration muscle tone reflexes in color uh each worth a maximum of two points so it's a zero to two point uh range so um i did kind of adding together scores for each of those parameters a total score about eight to ten is considered healthy uh of course there might be intervention required here if there's respiratory problems or if there's anything related to color which is oxygenation problems heart rate related issues or reflexes so the intervention may be required at this point but generally 8 to 10 is considered a healthy newborn what are some of the changes occurring in a newborn as soon as delivery has has occurred well the first thing that needs to happen remember all those shunts that we talked about the the liver shunt the doctor's venosus the ductus arteriosus which kind of helped the shunt in the pulmonary circulation all of the umbilical vessels the arteries the vein all of that needs to kind of revert back to uh what it should look like after birth but one of the most profound changes that the newborn is uh um having to adjust to is of course respiratory function baby taking its first breath requires a lot of effort because again those bronchioles those airways are very tiny and the lungs have collapsed at this point so you've got to literally open out all of those alveolar air sacs and this is where surfactant being produced in those last few weeks right before our delivery and birth is really important because the surfactant will reduce the surface tension and allows it a better chance to keep those alveolar spaces open so what prompts babies first breath well without the placenta without mom taking care of elimination of waste materials co2 levels start to increase inside of the the newborn and resulting in acidosis and that's what's going to stimulate respiratory control centers to bring about the first breath which is inspiration typically respiratory rate is is kind of elevated during the first few weeks and then it starts to decline to much more normal uh breathing rates um and again it's really important to have that is that an adequate amount of surfactant being produced which helps with respiratory function in the newborn so transitional period is the first six to eight hours or so after birth where you're going to see um vital signs being checked pretty um regularly to make sure that heart rate breathing rhythm oxygen saturation levels all of that is fairly normal uh in the in the newborn of course uh the the fetus have been developing throughout pregnancy uh surrounded in amniotic fluid so there could still be fluid um within the newborn that oftentimes the newborn may gag on it and regurgitate a lot of the mucus and the fluid uh and we sleep wake cycles at this point are not obviously regulated very well so there's a lot of waking periods that are occurring every three to four hours or so and uh going back to the fetal circulation and the changes that occur after the newborn is uh is delivered um remember we talked about the umbilical arteries becoming the medial umbilical ligaments and then the main becoming the ligamentum terrace uh all of this can happens within a few minutes or so after birth the ductus venosus this is the the liver shunt this could take uh transforming it into the ligament aminos and could take about 30 minutes or so and the the ductus arteriosus also becomes a ligamentum arteriosus again about 30 minutes or so the foramina valley which is the opening in the into atrial septum may take a little longer to completely close up where it transforms them the fossil values typically a few months or so after birth and could even take up to a year okay all right and the last few concepts i want to discuss here is lactation okay so as you approach the last few weeks of the pregnancy there's a lot of different uh changes occurring to the mammary glands in preparation for lactation which is a production of milk um so as the placenta ramps up um production of estrogen progesterone and of course placental lactogen these are the three hormones that are kind of important to stimulate the hypothalamus a hypothalamus is going to release prolactin releasing factor which then targets the anterior pituitary allows it to release prolactin prolactin is important for production of milk this is only going to start producing um a very different uh kind of milk initially but it takes about a few days to actually bring in true milk productions but prolactin is important for this process we'll talk about oxytocin that's also important for the letdown reflex but what triggers the lactation process is basically a combination of placental estrogen progesterone and placental lactogen as well that prompts the release of prolactin from the anterior pituitary so um the first milk that is released um by a lactating mom after the delivery of the baby this is colostrum this is very different from true milk this is less milk sugar less lactose much more protein content almost no fat content very high in rich in antibodies such as iga so provides protection against infections uh this the colostrum is what's released the first couple of days and this is then followed by true milk production so what allows for sustained milk production this is really um kind of like a stimulation effect so the more the need for milk production because of the the need for um feeding the baby so the the suckling of of a baby uh kind of triggers more and more milk being produced in inma okay and so prolactin is a hormone that actually produces the milk and prepares the um the breast tissue to store milk that is required for the next feeding so prolactin produces the milk but then the actual release of that stored milk from the mammary gland is brought about by oxytocin oxytocin remember was important for uterine contractions well the oxytocin also brings about contractions of specialized kind of epithelial cells in the breast tissue allowing for the release of stone milk from the breast tissue and this is called the left down reflex i'm going to show you what goes on here this is the last concept i want to discuss here so the more um the knee the more uh a female nurses or breastfeeds the more the stimulation from a suckling infant and that's what's going to basically uh trigger the hypothalamus to release oxytocin remember that oxytocin was stored in the posterior pituitary when the oxytocin is released this is going to stimulate the myoepithelial cells kind of like your muscle-like cells within the mammary glands causing these cells to contract and therefore the stored milk within the mammary glands uh is then released from the mammary glands um via the via the nipples and this is basically what we call the let down reflex so the oxytocin is important for the let down reflex the more um the mammary glands are going to release milk in other words the more there is need for it to be released for the infant that's in in effect going to sustain increased um production of milk within the breast tissue so the more that you have a let down reflux that that kind of informs the brain and then of course the the the breast tissue to to keep producing prolactin levels so the the more nursing that occurs or the more breastfeeding that occurs the more need for the hypothalamus to release um prolactin releasing factor which then allows the anterior pituitary to secrete the prolactin and the prolactin then targets the breast tissue allowing for more milk to be produced and be stored inside the breast tissue so prolactin from the anterior pituitary is important for production of milk which is stored inside the breast tissue but then the release of that stored milk is brought about by the oxytocin which is released by the uh posterior pituitary resulting in the letdown reflex and so there therefore there's a kind of a cooperative effect here uh the more there is a letter and reflex in other words you're releasing all of that uh stored milk from the breast tissue the more the need to actually produce more milk and therefore those prolactin levels go up that in essence is um how lactation is brought about after birth and the and the hormonal control from both the oxytocin and the prolactin in regulating that process i think that wraps up our discussion of this chapter so we discussed quite a few things here so we started with the fertilization event leading to implantation uh the role of hcg in keeping the corpus luteum viable during the early months of the pregnancy all the changes that are occurring in the developing embryo early on formation of the i mean how the the sensitive tropogloss allows for the whole implantation event to occur and then the transformation into the violated embryonic disc resulting in three germ layers forming which is grass relation you will need to know all the main derivatives of the ectoderm the mesoderm and the endoderm and then we talked about how all those organs are formed we talked about new relation and all of the changes occurring there and then we definitely talked about the formation of the placenta which is placentation and then you know the the the roles of the maternal and the embryonic tissues in the formation of the placenta uh we discussed a little bit about fetal developmental changes that occurs and then of course changes occurring in mom throughout the pregnancy then the final stages of pregnancy preparing for labor and delivery all the different stages of labor the role of oxytocin in antagonizing progesterone um the whole labor and delivery process and ultimately the the last thing that we discussed here was lactation so i think that pretty much wraps up our discussion of this chapter with pregnancy and base the basic developmental processes that occur in during embryonic and fetal development i hope this made sense to you and i hope you found this useful thank you