Oogenesis, Folliculogenesis, and Spermatogenesis

hi Ron Dr mikee here in this video we're taking a look at a process termed UAG Genesis and folicular Genesis and hopefully makes sense of these two important processes associated with the female reproductive system now to begin you need to understand that U Genesis simply refers to the uite also known as the ovam also known as the egg so this is any important gamet or sex cell associated with the female reproductive system now its job is to make sure that it has the right genetic material so that when it gets fertilized by a sperm it

can produce viable Offspring now the process of follicular Genesis is referring to the development of follicles that are these different cell types that can surround the ovam or egg and help nourish it protect it but also produce certain hormones that can facilitate this process of not just fertilization but also implantation of the fertilized uite so I want to begin not with UAG Genesis not with follicular Genesis but with spermatogenesis and you might be thinking this isn't why I turn this video on not to talk about sperm but to talk about the female reproductive cycle talking

about spermatogenesis first is a great launching off point it makes so much more sense I tell you why because the process of spermatogenesis which is to create viable sperm which is the equivalent of the viable egg is a much simpler process and so I can draw it out nice and easily and then you can compare o Genesis to it and see how it's different where and how so to begin with spermatogenesis we need to produce viable sperm and we do this because uh we do this by starting with a stem cell called a uh spermatogonia

right and if we have a look at this cell let's just take this C what we know about this cell is just like every other cell in our body it contains our genetic material specifically it contains 23 pairs of chromosomes so remember I were to pluck a cell out of my body and have a look there's 23 pairs of chromosomes a pair of chromosome one a pair of chromosome 2 a pair of chromosome 3 and so forth now it's a pair because I got one chromosome one from Mom one chromosome one from Dad one chromosome

2 from Mom one chromosome 2 from Dad hopefully that makes sense cuz it's very important because when it comes to sex cells like sperm like the ovom right or the Egg we don't want two copies we only want one from here and one from here because when they combine that's how we got the pair the one from Mom the one from Dad right so let's begin we've got our 23 pairs of chromosomes in this spermatogonia in this stem cell so let's just say let's just look at chromosome one so I've got got one chromosome one

here that's the one I got from Mom for example and one chromosome one here this is the one I got from Dad so we're just using that as an example now the very first thing that needs to happen in this process now this process begins at puberty this is important when it comes to spermatogenesis this begins at puberty now this what happens to this spermatogonia is first thing it needs to do is it needs to replicate so it needs to increase the amount of genetic material it has so it can undergo mitosis and it can

replicate now when it replicates what we have now is not just two copies of every chromosome right 23 pairs but we've got 23 pairs of chromosomes doubled up so I'm going to have that doubled up and I'm going to have this doubled up cuz we've repli replicated the DNA now what we need to do is we need to undergo a process called recombination so Rec combination is swapping some genetic material so chromosome 1 and chromosome 1 should be nearly identical there's going to be some differences but they're virtually identical and one arm from chromosome 1

and the other arm of chromosome one they can recombine they can swap Al swap genes right that's recombination so if we were to draw this recombination up we can draw it up like this these arms are crossing over for example and that's going to combine so this is recombination all right makes sense recombination now the next thing that happens in this process is we need to undergo meiosis so we've undergone mitosis which is simply uh doubling up the genetic material so we can split it apart into equal daughter cells we've undergone replication to double up

that DNA we need to undergo meiosis where we actually have the genetic material material into two cells so we take this and what this needs to do is it needs to undergo like I said meiosis and it does this because there's certain cytoskeletal structures which can help pull these chromosomes apart and so they start to hold on to these chromosomes and they start to pull them apart and so what you get is the splitting off right so you're going to have one daughter cell here and one daughter cell here now this one is going to

have remember it recombined right so this one's like this and this one is going to be like this okay we just underwent the process of meiosis how's that for rhyming we just underwent the process of meiosis so I'll draw it across like this so we just underwent what's called meiosis one but the thing is we need to undergo two types of meosis or two stages of meiosis because remember we only want one chromosome one because I want to mix it with one chromosome one from Mom right but here we've got doubled up chromosome we've replicated

chromosome one we've replicated chromosome one we don't want that so we need to undergo meiosis again so we undergo meiosis again and what we're left with now is if we draw up these four cells we're going to have that one we're going to have this one we're going to have this one and this one now what can you see here that's really important these four daughter cells which originally came from this have different chromosome one that chromosome one is different to that one which is different to that one which is different to that one we

call these because it's spermatogenesis spermatids they're immature sperm cell but what they develop over time in the test or testes is that little tail and now what we've ultimately developed is sperm ultimately now this is that second process of meiosis process of meiosis again so this is meiosis 2 all right perfect as you can see we hit the end point that we wanted a single chromosome because this one can mix with the equivalent chromosome from Mom this is what's happening now remember this begins at puberty and this will continue all the way to old age

basically to the end of life for a male right puberty all the way to end of life now I want to compare this with u Genesis which is a similar process but there's some important differences first thing I want to highlight here is we have that stem cell that begins it's not a spermatogonium right it's an UAG gonium and this is an early egg and again it's going to contain just like that chromosome one chromosome one right and it's the pairs 23 pairs of chromosones and it does the same thing it replicates right so it

replicates and we double it up and just like we had for the male reproductive system it's all pretty much the same so far including the recombination so we even undergo this process of recombination let's write this up recombination so that genetic material starts to swap over great and then what happens is it wants to start the process of meiosis so those important cytoskeletal structures come out to bind and try and start pulling it apart but here's an important Point here that's different for the female reproductive system compared to the male is that it freezes at

this point it stops now I said that for the male reproductive system this began at puberty right so what 10 11 12 years of age and goes to end of life for females this begins at prebirth fetal life gestation so when a female is in utero within their own Mother's uterus this process begins and this process goes from fetal life from fetal life this occurs it also from birth and puberty and in actual fact while this may begin at fetal life it doesn't go any further until puberty until puberty so it's frozen at this point

now this point is meiosis one right we've drawn it up here this is actually the beginning of meiosis 1 which is called prophase 1 so here we're in prophase of meiosis 1 and we're stuck at that point until puberty all right important thing to highlight here this is the egg right the egg contains the genetic material it needs to be viable so that when fertilization occurs from one of these viable sperm the genetic material can mix and you can undergo the whole process not just of fertilization but of the development of the embryo we need

to understand follicular Genesis because in the ovary where this is occurring this cell or I should say this uite needs to be nurtured protected fed nourished and so forth and this is what folicular Genesis is so inside of the ovary you have this uite right now if I were to draw the uite up like this let's just say that this thing here is that thing here what what we've got here is something that we call a primary uite so this is a primary uite and what you're going to find again during fetal development during fetal

development is it's surrounded by these relatively flat looking cells which are called pre granulosa cells pregranulosa cells and what we call this with the uite and the pregranulosa cells is a primordial follicle so this is called a primordial follicle so we' got a primordial follicle now the thing is that this primordial follicle doesn't stay as a primordial follicle it undergoes multiple processes of maturation and development this primordial follicle will turn into what we call a primary follicle so there's the uide again now the primary follicle these pregranulosa cells will turn into more cuboidal looking cells

that we don't turn pregranulosa cells now we just term granulosa cells granulosa cells but surrounding the uite we also have another structure called the Zona paluca here we've got the Zona palucci now I haven't told you anything about the granulosa cells or the zone of paluca simply put right now the granulosa cells help nourish that uite keep it alive make sure everything's okay the zone of paluca is a structure that surrounds the uite and is important when during ovulation when one of these sperm cells want to get into the o site and it penetrates the

zone of paluca it acts like a security system once one sperm cell has entered the zone of paluca sets down a cascading series of events which close that uide off so no more sperm can enter so this is not a primordial follicle anymore this is what we call a primary follicle now a primary follicle will also mature into a secondary follicle and the difference here is the oite gets slightly bigger the zone of paluca is still there the granulosa cells start to get a few more layers associated with them so you start to get around

about two layers of granulosa cells now but in addition to that you start to develop another cell type and this cell type are called ther cells so you now start to get these ther cells on the outside so we've got Thea cells we've got the Zona paluca and we've got the granulosa cells now what we've got here is not a primary follicle probably know what it's called now it's called a secondary follicle now let's just compare follicular Genesis with u Genesis right inside the primordial follicle the primary follicle the secondary follicle we've got this primary

oite this primary uite goes all the way here I told you this process here to prophase uh one of meiosis happens during fetal development during fetal development and it stays like that throughout birth it stays like that up until puberty however from fetal development through to birth through of puberty this process going from primordial follicle to primary follicle to secondary follicle continually occurs so we keep taking this cell and in here it undergoes this process from fetal development up until puberty right now up until this point what happens well this secondary follicle generally will undergo

a process called at treia which is death now I want you to think about this every single month what's going to happen is that 10 to 30 of these primordial follicles will undergo this process from fetal development all the way to puberty and they will all undergo a treia up until puberty which means that if we have a look at this this particular oite this primary oite if we were to have a look at that during around about 20 weeks gestation now what does that mean you're halfway through pregnancy basically so you're developing fetus halfway

through right how many of these do you have in your ovaries you've got around about 7 million but remember these get taken and undergo this process and continually die every single month 10 to 30 and what we end up getting in actual fact happens more than every month but we'll get to that point what happens is at by birth we've gone from 7 million to 1 million at Birth and then by the time we hit puberty we've got 300,000 now your question might be it makes no sense I don't understand why we would take this

prophase one cell that we've gone all the way to this point and just continually kill them off we don't know why this happens but it does happen until puberty occurs now what happens at puberty that's the important question generally speaking what happens at puberty is that this prophase 1 or meiosis 1 will complete now when it completes remember have a look we need to undergo this splitting stage right so puberty hits we need to complete this process so what happens is just like with spermatogenesis splits in two but what you get is this you get

a small cell and a big cell this small cell will contain half of the chromosomes that are replicated so this one's going to contain this for example and we call this a polar body throwing pens as usual this is called a polar body now that polar body can undergo the second stage of meiosis or not it depends sometimes it does sometimes it doesn't but this bigger one here which now contains this right here this is the main ovam or over uh oite that we're referring to this oite is no longer a primary uite now it's

a secondary uite all right now another important point to understand here primary oite secondary uite and then we have primordial follicle primary follicle secondary follicle don't mix the follicle stages up with the uite stages up because the uite to here is present to here that's important all right so we got this secondary uite now because we've undergone we've now completed the first stage of meiosis so meiosis has finally happened when pubid sets in so meiosis 1 is now finally complete compare that to the male reproductive system the whole thing started at puberty and goes all

the way through continues here puberty puberty hits mosis one completes all right that's important we've now got this secondary uite what now happens with this secondary us okay firstly what is it about puberty that stimulates this process well when puberty hits certain hormones are released so what you need to remember is that you've got your brain so here's the brain and at the base of the brain you've got your hypothalmus and you've got your pituitary gland like that now I know that mainly looks probably like a chicken more than anything else but here we've got

our hypothalmus and hypothalamus I can't read and write at the same talk and write at the same time Thalamus Thalamus Y and underneath you got the pituitary gland now the pituitary gland has two P see on you I shouldn't have pit my gosh not great today there's an anterior posterior it's the anterior that we're after here the anterior aspect of the pituitary gland because the hypothalmus once pubity hits the hypothalmus will release a hormone called gonadotropin releasing hormone and it travels down the blood supply to the anterior pituitary gland and the anterior pituitary gland will

release two more hormones it will release and I'll put them in red and black it will release what we call the gonat tropins now what are these gonat tropins these gonat tropins there's two types there's what we call lutenizing hormone and there's what we call follicle stimulating hormone now once puberty hits this process happens gonadotropin releasing hormone is released travels down this blood vessel that goes from the hypos to the anterior pituitary stimulates the release of the two gonadotropins lutenizing hormon follicle stimulating hormone and in actual fact they get released in a pulsatile fashion every

90 minutes throughout all of reproductive life so from around about 11 years of age all the way up until around about late 40s you get this pulsatile release and not only is it puls to every 90 minutes but it changes over 28 days which we call the menstrual cycle the uterine cycle the ovarian cycle so hip puberty these hormones are now released what happens is something important the luteinizing hormone follicle stimulating hormone that gets released they combine to receptors on these cells now some of these cells not every single one will undergo a treasure some

will mature a little bit more right some will turn what's uh turn into what's called um pre-ovulatory follicles or preanal follicles but in actual fact what they are is like this right you've still got the uite you've still got the Zona paluca you've still got the granulosa cells that are present so let's draw these granulosa cells we drawing it really rough here right they're usually relatively cuboidal in shape you have a whole bunch right and then you have these ther cells as well that surround and there's usually two layers of ther cells by this point

an internal and external and you end up getting this space that's present so see this space here this starts to get filled with fluid and this is called the antrum right so this starts to develop now what I'm saying is that once puberty hits there are receptors right so you're going to have from uh now this is called let's call this a preanal folle or preg graian follicle right there are receptors for lutenizing hormone and follicle stimulating hormone now the th cells have receptors for lutenizing hormone and the granulosis cells have receptors for follicle stimulating

hormone now I want you to think about this throughout this process right we hit puberty every month the menstrual cycle occurs what you're going to find is that there's going to be follicles at different stages so you're not just if I were to take let's just say day seven of the menstrual cycle and had a look in the ovary I'm not just going to see 10 to 30 secondary follicles right I'm going to see 10 to 30 follicles some are primordial some are primary some are secondary some of these preantral follicles right but then once

we hit a particular point in which in in this cycle follicle stimulating hormone luteinizing hormone starts to rise up right so it starts to go up day five day six it's starting to rise right they're going to bind to receptors now these receptors are located on all the different types of uh the primary follicles of granulosa cells and theer cells and so that includes here right so let's just say on the secondary and let's compare it now to this one so they're going to bind to luteinizing hormone and follicle stimulating hormone so luteinizing hormone at

the Thea and follicle stimulating hormone at the granulosa all right when they bind they stimulate both because I haven't really told you what they do the granulosa cells and the ther cells together they produce estrogens now specifically the estrogens that they produce are estral estral so they produce together estral so let's do an arrow here and write let's just write estrogen and because I'm in Australia let's spell it properly estrogen so together they do this now they actually do this because they need they rely on each other right so the ther cells can help produce

androgens like testosterone and then hands those androgens off to the granulosa cells that can turn the androgens into estrogens like estral so the estrogen's now released now what this estrogen does is it travels to the uterus remember the whole point of this whole process is we want to ovulate an uite that can be fertilized and then embed in the uterus specifically the endometrium so the release of estrogen during this phase stimulates the uterus to thicken and become more vascular right preparing for implantation but because of negative feedback that estrogen will travel back to the brain

and specifically tell the gonat tropins to stop releasing and the anterior p AR gland to uh the Gat tropin releasing hormone to stop being released and the g Gat tropins to stop being released that's negative feedback which means luteinizing hormone stops getting released follicle stimulating hormone stops getting released okay this is weird what's going on all right when pubity hit and those hormones were released and bound to those cells specifically FSH stopped some cells from under going a treas you remember 10 to 30 prepuberty went through this process and just died off right they just

went through this process and died 10 to 30 every single time but puberty hit these hormones are released The Binding of these two specifically follicle stimulating hormone it's all in the name right would stimulate or save some follicles from a treasure to move on to the next stage right a subset of this 10 to 30 and as they continue to grow and divide they start to release estrogen of the surviving ones start to release estrogen this estrogen inhibited the release of more FSH and LH that's important because then it stops any more follicles from moving

forward and of the follicles that have move forward you're going to have one out of all of them that's going to be the most mature this one like this one here because it has more granulosa cells and more thicker cells it's just going to have more receptors for H and FSH and even though they've been blocked and stopped whatever's remaining are going to stimulate these ones cuz there's just more receptors for the very little remaining and all the rest will die off all the earlier ones will die off because they don't have enough receptors to

bind to the very little FSH and LH remaining so they're not selected for they die and then the one that's remaining is the one that's selected for and this preanal or graphium follicle it will turn into a graffian follicle or a mature follicle now this graphion or mature follicle let's just say it's now turned into that right this graphin or mature follicle has so many Granulos and Thea cells that it starts to produce huge amounts of estrogen right huge amounts of estrogen so the estrogen levels really go up now I said that here when these

cells produce you know a little bit of estrogen it results in negative feedback so little bits little amounts of estrogen results in negative feedback but if you pump that estrogen really high it actually and we don't know why it results in positive feedback so now it goes back to the gonadotropin releasing hormone and says pump some more out which then goes to the gadat tropin and says pump more out and now we pump out a bunch of luteinizing hormone and follicle stimulating hormone in this case now it's the luteinizing hormone that we're after and what

happens is the lutenizing hormone tells these Thea cells for example to start releasing releasing enzymes that start breaking down the Walls here and what ends up happening is you with from the release of LH right luteinizing hormone now what it does is it results in ovulation here are the ther cells here are the granulosa cells and the Egg the uite ovulates and it's going to be surrounded by just a couple of granulosa cells so what we have here because of that luteinizing hormone we have ovulation now this happens at day4 of the menstrual cycle now

let's just compare this uite where is it what's happening all right let's think about this so This secondary oite the one here this is actually the one that gets ovulated this uite is that oite it's the one that gets off so that's a secondary oite now right it was a primary uite up until around about this point now it's a secondary uite which means it's turned up to this phase now once ovulation has a occurred what we need to undergo is a second phase of meiosis so it starts the second phase of meiosis but freezes

again and waits now what's it waiting for well in actual fact it's waiting for one of these sperm because this is now ovulated it's ovulated into the fimbr right of the uterine tube and moves its way down into the Ampla like the neck of it right and here it waits for any sperm to come up to fertilize it so if one of these sperm let's just say this one here so remember this uite has that genetic material inside right and it's waiting for a sperm to come along now if a sperm comes along and fertilizes

it now remember this sperm is going to contain its genetic material which is just that one ch so it's this one that got selected right that's the lucky sperm once it has fertilized that secondary uite it now stimulate it to finish meiosis 2 remember meiosis 2 is happening here very simply with spermatogenesis we can't finish uh meiosis 2 unless the sperm fertilizes the egg and so in this process you get what's happening again and you get another polar body right because we need to pull one of these replicated DNA off so we get one polar

body right and then what we're left with is a fertilized egg that's going to have that chromosome from the sperm and then this chromosone from the uite and now what we've just completed is not just the first meiosis but the second meiosis and what we've now left with here is what we call a mature uite a mature oite and so as you can see this mature uite occurs after feralization so have a look right start off with a primary uite it begins at fetal development in utero it replicates recombines and freezes at prophase one of

meiosis one Freez there up until puberty but throughout that process this is undergoing primordial follicle development to primary to secondary maybe a little bit further but because there's no FSH and LH prepuberty at least not at the level that it requires it just undergoes a treasure and dies so the number of these uyes diminish from halfway through gestation you got 7 million at Birth you got 1 million and at puberty you got 300,000 left then once puberty you undergo a more regular cycle of 30 of 28 days and every 28 days 10 to 30 of

these continue to go through this process but now we've got LH and FSH available which saves some from at treia to become more mature the most mature one gets selected for produces huge amounts of estrogen which boost out luteinizing hormone that stimulates ovulation once ovulation has occurred right so this is the one that gets ovulated it is in the uterine tube and the sperm can come along and fertilize it and then it under goes the second meiosis or completion of second meiosis and now we've got the mature uite that contains the complement of paired chromosomes

one from Mom one from Dad it's this that can develop in utero implant and develop into an embryo and so hopefully this is a simplish overview of U Genesis and folicular Genesis hi everyone Dr Mike here if you enjoyed this video please hit like And subscribe we've got hundreds of others just like this if you want to contact us please do so on social media we are on Instagram Twitter and Tik Tok at Dr Mike todorovich drr m i k e t o d o r o v i c speak to you soon