Prenatal Development - From Conception to Birth - Germinal Stage, Embryonic Stage, Fetal Stage

this is my son the first time we met he was no bigger than a raisin yet today he has a full body functioning organs and nervous system and consciousness so the question we're going to answer in this psych explaining video is how does a single cell turn into a human life [Music] alright guys welcome to psych explained in this video we're going to talk about the amazing nine-month journey of life or more specifically the three stages of prenatal development now before we get to the stages what i want to first cover are the major structures and cells that make life possible in the first place we're going to start with this diagram here it's probably something you've seen a thousand times online in textbooks and this is the female reproductive system so let's just make sure we are understanding what we are looking at so a couple structures i do want to point out the bottom structure right here is what we're going to label as the vagina and this would be the birth canal right sitting right above it is what we call the cervix okay when a woman is about to give birth and doctors say she's three centimeters dilated five centimeters dilated what they're referring to is the opening of the cervix which remains closed during pregnancy and then we have this entire body that's the womb that's going to house the entire uh embryo is what we call the uterus right or the wound the uterus okay there we go so the vagina the cervix and the uterus now all the really important structures we have this structure right here we're going to zoom in in a second this would be the fallopian tubes okay or the uterine tubes and what houses all the eggs that have potential to become a human being in an area called the ovary and this would be the female gonads while the testes would be the male gonads so we had a vagina cervix uterus lobin tubes and ovaries and what we're looking at here is a zoomed in version of this cross section so we have the uterus or womb this would be the uterine cavity the wall or lining of the uterus the fallopian tube we'll talk about the purpose of that and we have the ovary sitting right here so those are the major structures now what about the major cells or reproductive cells that are vital to create life in the first place and that's what we have right over here and we'll talk about why it's sitting over here in a moment now there are two main reproductive sex cells needed to create life now what's important to know is that these structures together have a name do we know the name any reproductive sex cells is something that we call gametes okay gametes and they are different depending on if you are male or female so for example the male gamete would be we call a sperm cell sperm cell and in the female this would be called an egg okay or ovum put that in parentheses all right so that's the gametes that are going to be needed to create life now what's really important to know we'll talk about this later on as well is that within each gamete is a nucleus so we have one nucleus inside the eggs and we have one sitting inside the sperm cell now why is that important because with inside the nucleus is all the genetic material that's going to make you you determine the color of your skin the texture of your hair um how tall you might be your weight predisposition to diseases so this is gonna take could date all of our genetic material now what structure is uh houses that genetic material we call that chromosomes right now you might be thinking is there 46 well not in gametes in gametes they only have one pair because they have infused together so and so instead we have 23 chromosomes in the sperm cell and we have 23 chromosomes in the nucleus of the egg cell okay so that's just important to know and we'll come back to that later on all right so there we go we have our major structures and we have our our reproductive cells to create life all right so let's start with the first stage of prenatal development we're going to come over here the first stage that we need to know and this is where it's really going to start and this is considered well i'll get to the dates in a moment is called the germinal stage say with me what is it called the germinal stage and how we're going to remember it's called the germinal stage well everything at this moment is pretty microscopic it's almost the size of a germ right that's a really nice memory technique and in terms of dates this is considered pretty much the first two weeks after fertilization and we'll talk about what fertilization means as well so let's say day zero to day 14 right the first two weeks of life okay so what is actually happening now we're going to talk about this in a moment which is the fact that we're going to think about the journal stage as a sequence of events and we'll talk about what the first uh what the first stage is but let's start over here okay now in order to actually have life you have to have an egg okay so where are the eggs stored well the eggs are stored and we'll come back over here in this structure right here called the ovary and i've already mentioned this is just kind of a zoomed in version of the ovary okay and you have all these little tiny eggs okay now at the moment they're not actually mature eggs okay they're like teenagers they're not right they got some issues they get they need some time to to become an adult in fact an immature egg is what we call an oocyte what's it called an osi so we have tons hundreds of thousands of oocytes within the ovary now how are we going to get the ovary out of the ovary or the the oocyte out of the ovary to get ready to be fertilized well it begins with what we call the menstrual cycle okay the phrase menstrual cycle basically means the body of a woman is preparing itself to get pregnant so what happens well one thing that happens during a menstrual cycle is the thickening of the uterine wall so the uterine wall actually gets thicker why is that so when the egg comes out of the fallopian tubes okay all here it's going to implant itself embed itself in the uterine wall it's kind of like a cushioning okay so that's kind of one part of the menstrual cycle the other part is what we call and we'll write this in in a different color is what we call ovulation uh viewlation okay so what is ovulation ovulation is the release of an egg okay so eventually these oocytes have to pop out into the fallopian tube well how's that gonna happen well the first thing that's gonna happen is this ovary is gonna release a lot of hormones can you think of any hormones that might be released by the ovary well if you're thinking estrogen or progesterone is another one you're correct estrogen okay so we have this kind of a surge in estrogen now we cannot talk about anything in the body without talking about the brain so here's what we have the ovary is going to communicate to the brain how's this going to work well let's draw it here as the estrogen floods our blood okay this information and i'll move it over here is going to head up to the brain okay now what part of the brain would this go to all right let's think about all of our our biology knowledge what part of the brain controls the entire endocrine system right it's the executive command center that kind of regulates the hormones in the body well if you're thinking i think that's the hypothalamus you are correct hypothalamus okay let's do something like this hypothalamus okay and the hypothalamus is going to trigger another gland we call this the master gland this is the pituitary gland okay that kind of sits right below it okay so hypothalamus is going to talk to the pituitary gland and what this is going to do i'll just write pg pituitary gland right here is it's going to release tons of hormones into the blood in reaction to the ovary right the ovaries communicate with the brain and the brain is going to communicate back and it's going to release a lot of different hormones that are going to make its way back to the ovary now this is more technical than we need to know but things like you know follicle stimulating hormone or luteinizing hormone and the reason called follicle stimulate follicle stimulating hormone is because all these oocytes are surrounded by follicles okay like the the house for the egg or house for the oocyte okay those are follicles okay once this information gets back to the ovary okay as we kind of have this you know feedback loop what's going to happen this egg is going to pop out okay and there we go with the egg and what are we missing the nucleus right the 23 chromosomes we have the nucleus okay this is essentially ovulation right this is part of the menstrual cycle and what's going to happen is this egg okay is going to start moving [Music] down the fallopian tube okay and by the way these hands little hair this called fimbriae they kind of grab the egg and then there's kind of little you know like hair cells down here that are kind of grabbing and pushing the egg it's very philosophical i just imagine like hands taking the egg ready to you know be fertilized for birth it's a very philosophical kind of moment here but here we go we have the egg going up here and we'll actually have the egg continue to travel to about right here now what has to happen well the egg has to have another gamete a male gamete to become a human being so what do we have we need sperm cells okay so let's have our sperm cells down here upon ejaculation and here's my sperm cells okay and of course what do we need we need our little nucleus this is very important okay around two to three hundred million sperm cells are released at one point i want you to think about that two to three hundred million but only one is going to fertilize the sec which begs the question if it was a different sperm cell would you be you would you have the same consciousness or to be an entire different person right those are the questions i want you to be thinking about and these sperm cells are going to be making up their way up the vagina through the cervix opening to the uterine cavity right and they're going to make their way now some are going to die some are going to get lost right someone go to the wrong fallopian tube and like where am i you're in the wrong fallopian tube but the sperm cells that go are going to make their way down the fallopian tube and there's one just one that is going to touch the egg okay it's going to touch the egg it's going to release specific enzymes and what's it going to do it's going to penetrate or burrow itself into the egg okay and what's going to happen is going to release its nucleus into the oocyte okay into the egg the moment that happens these two nuclei are going to fuse together okay how cool is that the moment this occurs what would happen this is called we're right over here together this is the beginning of our of our journey this is called fertilization fertilization okay so fertilization is the union or mixing together of a sperm cell and egg cell uh and our two nuclei now remember our chromosomes we have 23 and 23. now what do you think we have if you're thinking 46 you are correct okay so we now have 46 chromosomes now this egg is still going to continue down this track right it's almost like the sperm go this way and then the eggs going this way and by day one and we'll write this in two by day one we now have essentially a new human being okay with dna from the mom maternal and dna from the dead paternal and this single cell do you know what the cell's called this is called a zygote okay a zygote and this is going to be kind of next on our list of sequences we go from ovulation to fertilization we've created a zygote okay right here and this zygote is going to continue on the journey now what's important though also i think this is just kind of interesting is this egg really had two destinies it either a is going to continue to remain unfertilized and just go down the fallopian tube and bypass the you know the uterine wall and just come out through a menstrual cycle that's called a menstrual period right along with the uterine lining that's what a period is the other destiny is fertilization right so those are the two destinies of this now what happens after we have a zygote what we're going to have is rapid cell division this zygote is going to replicate itself over and over and over and over again right so we have fertilization zygote and then we are going to have cellular cellular division now another name for cellular division at least in this process is what we call cleavage okay so cleavage is when we have the replicating of these cells so what would that look like well we have one cell which by day two i'll need a bigger egg here now isn't right it's not an oocyte anymore it's actually an oval it's an egg is going to start dividing into and now we have two nuclei right so this would be the two cell stage what do we have to that after that we're gonna turn into four okay remember it's keep it's this this this o side this egg is is continue moving this way and then we go to well just keep adding it right now go to the eight cell stage and i'll see if i can get some sort of you know eight cells one two three four five six i'll do seven eight there we go there's my weird eight cell stage eight cell okay and then we have we'll go to the 16 cell stage and i know i'm not going to have exactly 16 but you get the point right 16. now at this point this is actually called the marula okay i could actually write that in the marula and it's named after that it looks like a berry right like a raspberry and this is kind of a clump of cells okay a clump of cell now what's really important to know is this structure is the same size as the original zygote it's not a giant structure it's just the the cells are just really compact all right so that's really important though this is not bigger it's just you know clumped together okay all right now here's what's important the last big structure to evolve after the marula right before implantation okay and this is going to be tons of of cells is what we call and i'll write it right above it as well [Music] is called the blastocyst blastocyst okay and what's amazing about the blastocyst is that it's actually hollow there's nothing on the inside except for fluid on one side and a couple cells on the other side so we can actually draw that together right all the cells are on the outside now you can get very technical you can watch you know hours of youtube videos just on the marula just on the blasters we're not going to get that technical but there is a name for the outside cells okay and you have a little clump of cells on the side right here okay and the reason that's important at least the blastocyst is before is because the cells are starting to differentiate right everything has a purpose the outer cells are going to develop into something we'll talk about that in a moment and the inner cells are about to develop into something okay so actually write that in right over here the blastocyst is gonna be one of our major structures blastocyst and then finally what do we have we have implantation okay this big blastocyst is going to embed itself into the uterine wall okay and also you can watch hours and hours and read tons and tons just on implantation but we're not going to get that technical okay so it's going to implant itself there a little after a week and it's going to be there hopefully for nine months okay so there we go let's recap oh by the way let's write implantation down here that's our last stage so here's what i was meaning about the german stage think about it like a sequence of events we start with ovulation the release of an egg we have fertilization the fusion of our two gametes we create a single cell called a zygote we have rapid cell division or cleavage we create a blastocyst and finally that blastocyst implants itself in to the uterine wall all right so there's our first stage let's talk about stage number two stage number two which is a big stage is what we call the embryonic stage embryonic stage okay or embryogenesis is like whatever happens during that stage instead of the first two weeks this stage is considered week two to about week eight okay now the embryonic stage is really important if you take a look at all the structures here it starts to actually resemble a human being we have little buds little arm buds and we have leg buds you know eventually this is going to look like an alien you you'll you'll actually have an eye right you'll actually see it won't be open you'll have an eye so you start creating real life now to come back to the embryonic stage i want to come back to the blastocyst let's actually draw that together and i'll draw almost identical to what we had right we have cells on the outside eventually this outside membrane is going to you know detach itself okay we have the cells on the inside on one corner all right now the reason this is important because during the stage things are going to change everything has a purpose what we find is that the outer cells and we call this the outer cell mass is going to develop into we call the placenta right everything everything's differentiated everything has a purpose now okay we'll talk about the percent in a moment and what do you think about the inner cells well the inner cells the green are gonna develo well instead of outer cell mass is the inner cell mass inner cell mass is going to develop into the actual embryo with a head and a body this is gonna become the baby the embryo okay so that's why this is really important the cells start to differentiate now what is the placenta just very quickly the placenta is down here okay uh i'll actually label it it's this structure right here the placenta and what the placenta is is that's a it's an organ and it helps nourish the baby it gives nutrients and oxygen to the growing embryo and also removes waste from the embryo's blood it's essentially the lifeline between the mom and the baby so whatever the mom consumes so does the baby through the umbilical cord right attach the belly button and that's how the baby receives nutrients or removes waste so mothers remember whatever you eat so does the baby whatever you drink so does the baby okay there's the placenta and the umbilical cord all right so what happens next well what we're going to write i think i'll use this marker is is the actual development of the baby i mean we have so much information right here so what we're referring to instead of cell division right instead of cellular division what we're going to have is cell differentiation different okay i'll use red so division of differentiation which means that all these cells now have a purpose and they're going to develop into something what are they going to develop into well we're going to start having all the systems of the body develop everything you need to live and be a human being so we have things like you know the nervous system is going to develop now not entirely right it's actually a neural tube you know we don't actually have a functioning brain but the cells that will create a nervous system will be there uh the urinary system the bladder right the urinary system and by the way as i'm writing this just start thinking about other systems that i'm going to write down right we have the uh circulatory system right heart system okay what else do we need we need to breathe right so we have the respiratory system system and maybe just one more right there's many of them the digestive system [Music] right so the majority almost everything that a baby needs to live from heart lungs kid needs gonads is going to well gone later is going to start creating uh during the embryonic stage now you'll notice i have a little graph down here okay why is this important well because so many things are developing during the embryonic stage it is most vulnerable and susceptible to bad things so what do i mean by that well this little asterisk right here is what i was going to write down something called teratogens okay what is a teratogen a teratogen is any substance a mom consumes that or exposed to that could affect the growing embryo so it could be alcohol it could be um nicotine it could be radiation it could be mercury anything that they should not be exposed to that can cause birth defects um language delay intellectual disabilities all those things right there we can even look at it on a graph what this would look like so we have stage one two three right this is the germinal stage and the embryonic stage and this is the risk right the risk of something bad happening to the embryo or or baby growing baby and if we take a look at this graph i'll use this marker what you can see something like this is that the greatest risk is during stage two the embryonic stage right all of this are things that could happen because of all the systems that are developing okay so make sure mothers that we take care of ourselves especially during weeks to date now this is not to say that you know in week 27 you can just start smoking cigarettes that's not what i'm saying but the baby's less likely to be impacted than during this stage okay so here's the embryonic stage and we'll come back to stratagems at the end we come back to factors influencing development all right what is the last stage we go to germinal embryonic and finally we have the fetus the fetal stage okay the fetal stage and as you see we have a lovely you know full baby and this is considered the kind of final stages so we'll say week 9 to about 38 38 weeks to 40 is considered a full term baby now at this point everything is pretty much developed right it just needs a little more time in the oven right so to speak so what we're really referring to is the kind of the final you know the final growth growth and development okay and this could be right we have the brain so if we look up here we during the fetal stage we're going to start having right our brain and we'll have our spinal cord develop it's no longer a neural tube but it's actually a spinal cord um the kidneys are going to start to function um the liver right all the things the organs everything we need to live outside the womb is going to finally complete whether something like the gonads right the female male genitalia that's about week 13 14 on ultrasound you can see whether you're having a boy um or a girl now other things that might develop during the stage is human features in other words the things that make us look human right besides just a final growth and development like skin is gonna develop and and hair okay and nails right so everything that's going to make us look human is going to develop as well and the final thing i'm going to write down is the baby is actually very active we don't see this in the other stages so we have activity and uh coordinated reflexes reflexes so the baby might have a grasping reflex they might suck their thumb um they're gonna kick um they they can hear the mom's voice or hear the outside world so they start responding to environmental stimuli the baby is ready for the outside world now before we finish it's important to know what are the factors that are going to influence this whole process now you'll notice i divide into nature and nurture do we remember what the difference is all right nature is anything genetic right inherited and nurture represents things in the environment so let's start with terogenes where do you think teratogens would go on the spectrum of nature nurture if you're thinking maybe around here you would be right right teratogens are from the environment dorado genes okay as i said before alcohol nicotine those type of things right if somebody drinks too much alcohol that can cause fetal alcohol syndrome fas that can cause intellectual disabilities we also have things like the health of the mother right um obesity diabetes those things can can affect um and even things like stress right stress can uh maternal stress can have a big impact on the baby right these are things from the environment so we'll go on the nature side well there could be genetic abnormalities right things that are passed down from the mother or father uh things like huntington's disease or sickle cell sickle cell anemia right these are things that are part of the genetic code or issues with the chromosomes chromosomes uh like down syndrome which is an extra chromosome on the 21st pair or partial chromosome um or klinefelter syndrome so you do have genetic and chromosomal as well now we used to say in psychology nature and verse nurture we don't say that anymore we say nature and nurture okay nature and why because these can influence one ano one another there's a great term in psychology that's starting in a lot of publicity that's called epigenetics okay what this means is that whatever you're exposed to in your environment can have an effect on gene expression right so if you grow up in a really healthy environment you might have a gene for a mental illness but it's not going to show because you grow up in a good environment but if you grow up in poverty or an impoverished environment that gene might express itself and then you develop a mental illness so epigenetics is explaining the idea that there is a connection between nature and nurture all right guys thanks for watching i really hope you learn about the journey of life it is truly amazing and it's still shocking to me how a single cell turns into a human being don't forget to like the video subscribe see you next time

Channel: Psych Explained

Views: 47,927

Keywords: prenatal development, embryo, fetus, teratogens, blastocyst, oocyte, morula, cells, gametes, zygote, fertilization, conception, implantation, uterus, fetal alcohol syndome, cleavage

Id: wdrtD9cEQwo

Length: 28min 53sec (1733 seconds)

Published: Fri Aug 19 2022