welcome to this short lecture on spermatogenesis this lecture will essentially cover the process of how we go from a stem cell into a mature sperm and also we'll understand the terms spermatogonia spermatocytes permitted spermatozoa swimming Genesis thermogenesis so for this lecture we're going to focus on three major images we've got this one over here which is a flow diagram which is just illustrates how the cells moves through the different stages of meiosis we've got starting from the stem cell moving all the way through it down to the samaritans over here we've got an image here of the testes more focusing on the seminiferous tubules which we'll go through in a second and then finally over here this is focusing on the embryology so how does the cells all begin with so let's begin with embryology now in this particular case the starting of the cells to produce sperm come from a type of cell called the primordial germ cell so going back to 12 going back to two weeks fertilization there is two blankets of cells two layers of cell known as the bilaminar disk on the top layer we have these cells called epi blasts so there's a group of cells coming from the EPI blasts that migrate into an area known as the yolk sac now this is so this would be the head of the embryo this is the tail end of the embryo this is the amniotic sac this is the yolk sac which is going to help develop some of the intestines so a group of cells in this region here known as the primordial germ cells so they migrate and start to cluster in this area now these cells will start at about the fourth the fifth week will start to move back into the embryo now they'll go into an area around the level of t10 so thoracic 10 region and they will go into a group of cells like a mess final group of cells known as the genital Ridge these this bundle of cells the genital Ridge essentially is just on the side kind of medial to where the kidneys are developing which is the pro and Mesonet raus so this genital Ridge is where these cluster of cells called the prime model germ cells will migrate into they kind of migrate through like this cytoplasm membrane action where they kind of crawl their way into that particular area and as they integrate that genital Ridge will start to differentiate into something more similar to the gonads so when we go now this is about the fourth fifth week as it's doing this migration as it starts to integrate into the maze and crime will start to have further differentiation into the stem cell which will make the gametes so for the female it's going to be the over Gonia for the male it's going to be this format Agana and then we have the support cells so as it goes into this bundle of the ridge of the genital Ridge these cells will start to differentiate slightly different depending on the hormonal situation and other signaling so if you could imagine this part which is going to be the testes this is the genital Ridge and the germ cells or the primordial germ cells will go into it if this bundle of Ridge is going to develop into two parts which is the the medulla cords or the medullary sex cords or the cortical sex cords now if biologically it's going to go down the female line it's going to differentiate more into the cortical cell lines so this is going to develop the OA Gonia and the follicular cells but for them for the males this is going to go down the medullary sex cord lines which is going to develop into these lobules okay so these lobules in the testes so this gonad is now going to differentiate into a male phenotype so these sex cords medullary sex cords are going to develop these things called a lot so as we move towards birth these lobules are going to number about 250 now in each one of these sex call sex cords we're gonna have two major types of cells now if I was to have a look through this kind of convoluted tubules called the seminiferous tubule in the whole lobule itself so as I was saying there's 250 lobules within at-st and this will give you a significant volume of the testing within each lobule you have approximately one to four seminiferous tubules which you can see these squiggly lines here a big long tube convoluted tube that will go up towards this end now with the testes being developed you have another duct system that comes into it so this comes from a different system not the genital Ridge I will explain this process in a separate video when we go through the development of the genitourinary system but the ductal system from a separate system comes in to the developing Ridge and that grows together so this is going to be the duct or the vas deferens with the epididymis and then the communication will come down with a developing genital Ridge which is the lobules going into the reti testes into the epididymis now in each lobule you'll have one to four seminiferous tubules which is gonna be this long convoluted tubules if I cut through this and look here so in so now we've been born so the baby's been born and we're going up to a point of pre puberty so if I was to look and focus in on here it would have this outer basal lamina okay and inside this tibial you will have this blue cell which is the stem cell and these green cells called the sertoli cells these are probably homologs to the follicular cells in the female so these are supporting cells but as you can see this whole the seminiferous tubules is completely filled with these cells there's no canal's so they have to be further hollowed-out a bit later on when we go into puberty but just full completion remember there's gonna be a whole lot of these all around each other so all of these areas just filled with tubules because they are convoluted and in between the tubules is the interstitial which the cells that mostly accumulate in the interstitial are going to be things like Leydig cells and my outsider mired cells which is important for contraction okay so when when we move towards puberty the majority 80% of the testee is essentially filled with seminiferous tubules in these lobules so a significant part of the testee volume is going to be in these tubules okay and if you were to quantify it add up all the lengths of these tubules you will essentially probably have 250 to 300 meters worth of seminiferous tubules now before we go into the actual development of the cell I'll bring you across to this particular flow diagram to show you how it actually occurs from a very simplistic point of view so this whole process from a stem cell all the way through to a spermatid okay which is kind of an immature sperm to the point where we have sperm that's now mature this whole process is known as the matter Genesis however the last part of it where we go from a spermatid to a mature sperm this is known as sperma Genesis so let's start at the beginning so here we have a stem cell which essentially started off from the primarily germ cell so this stem cell is sitting at the basal lamina the most lowest part within the sertoli cell which I'll get to in a second this is the stem cell that makes all the sperm okay so it essentially will replicate into what we call a dark type a spermatogonia so okay so the reason why it's called is because the way the chromatin so that the way the nuclear material is arranged it looks dark in histology now this cell will essentially do two things it will just go through mitosis and then just go back on itself to continually create a pool of cells that will always be there full for the production of sperm through the whole age the whole life of the male so we do have a population of the type a cells that just keep going in this circle but there is a group of Taipei's that will differentiate into what we call a pale type a into a type B cell so these are now essentially going into a type b spermatogonia which has 46 number of chrome of the DNA chromosomes with an XY so it's got double the material essentially as a normal somatic cell now this particular cell will then migrate into what we call a primary spermatocytes so we're now ready to essentially go through the first stage of meiosis one so this is going to be myiasis one from the primary so that's meta site into the secondary spermatocytes so this is the largest cell out of the whole lot so through this whole flow process the primary spermatocyte is the largest out of a lot now the primary spermatocyte will break into two secondaries through meiosis one and so you're basically half in the amount of genetic material so with the secondary spermatocyte essentially what we do now is have it again and so we split it through meiosis two and now we let so now we're gums from diploid into a haploid and then we split again into another by simple form and these are what we call sperm attitudes okay so essentially from one cell we go into for sperm attitudes so that's essentially the the process the flow process of how we go from a stem cell into spermatids and then we're going to go into a maturing but what we're gonna do here is now jump into the actual testes to see the process actually occurring so as I said if you were to look at this in the pre-pubertal stage this the seminal never of tribulus will be all filled with these types of cells the most abundant cell will be the sertoli cell and you're going to have the other type of cell within the tube you'll being the the germ cell which is going to be that one but as we hit puberty and the hormones start to change things like follicular stimulating hormone and luteinizing hormone which is going to come up from the church' glen come down from the tree clam it's going to have an influence on two major cells one being the green cell which is the sertoli cell and one being outside here which is in between here so it's going to be sitting out here being a laid egg cell so here gonna have a change in testosterone and the way that the sertoli cell which you can see is arranged here it's going to now arrange itself like so so if you could imagine this basal lamina is going out around like this so i couldn't draw at all but you could probably imagine that this would continue around in a big circle and in here in the middle is the loop the lumina which is the canal where it's going the sperm is going to move through okay so the sertoli cell kind of as it because into its adult form will start to look more like a column columnar or more like a cuboidal shaped cell but a lot of this is this is the nucleus and the the way that the cell arranges this is kind of like a plasma recess so this is a whole lot of tissue or whole lot of cytoplasmic tissue that the developing sperm is going to be nourished within so one of the primary functions of the sertoli cells is to actually nourish the cell as it moves through into its mature form it's also going to play around with some hormones particularly the hormone or called a BP which is antigen binding protein but it's also going to another hormone cord inhibin okay which is probably going to feed back up into the pitcher gland and change the speed or the way that this spermatogenesis occurs and also it's going to produce a fluid to help move the sperm along the the tube you'll up into towards the epididymis so now we're going to focus on the process of how we go from a stem cell and go and produce a mature sperm so down here we've got the stem cell so this is the stem cell spermatogonia cell which is this one it's going to replicate like so and it's going to produce a dark-type a cell like that like this one this will essentially feedback and this process will just continue to maintain that pool of cells but some of these type-a cells will much more differentiate into a type b cell which is going to be here this will further through mitosis copy itself okay and then go into a primary spermatocyte now it's important to note here that the sertoli cell has kind of two parts to it it has a basal apartment has an ad luminal part now there is kind of like a tight junction between the two which is kind of like a blood test ease barrier which is important for immune function to stop the immune system essentially attacking or possibly interfering with this process and the important point here is as we move from the primary into the secondary you'll have to kind of move through that tight Junction or that that area where it it kind of inhibiting the communication between the two also the Satomi's neighboring each other have other tight junctions which seal them off which all that also allows that blood testis barrier from the primary it's the motor site which were here as we said we go through meiosis one which produces two secondary spermatocytes so gone from van Agana now to the medicines from here we then have again and we go into the spermatids as we move towards the Lumina of the luminal region so the the canal of the seminiferous tubules so this is going to be in the middle part to be transported up into the epididymis so we're really in this point here which is now sperma Genesis so the process that I'll go through quickly is now how do we go from our immature ass permitted which is this particular cell here which would be these ones into a mature sperm so there's a few steps that occur here so as we've copied into the spermatid which is here we have to do a few phenotypical changes to the cell to make it ready to be a active sperm one of the first things that we'll do is we'll the at the Golgi body will produce these kind of lysosome in all bodies which are enzymes and these enzymes is going to be the acrosome this will start to arrange itself kind of in the front end of the nucleus so the front end of the nucleus which is important to be the head end of the sperm now what further happens is the cytoplasm starts to pinch off which gives you the appearance of the acrosome will sit at the front end of the sperm with the nucleus behind it at the same time we start to have these approach protein like contractile units that will start to come off the back end of the the nucleus and go towards the tail end these are going to be now the the membrane itself starts to pinch off and go dorsally and this is like cilia but it will eventually go into a flagella these protein like contractile elements which there are nine in number start to go parallel in that part of the the cell and we also have mitochondria that start to increase in number and accumulate just behind the nucleus which is going to be the mid piece of the sperm and the mitochondria is going to be important for producing the energy to propel the flagella and move the sperm along finally what we see happen is the excessive part of the cytoplasm which is this part here will get phagocytosis and taken up back by the sertoli cell and then the sperm itself or the somatic Gonia is but spent a sudden that Izawa will detach from the sertoli cell and now sits in the lumen from here the fluid that sertoli cells make which is a protein-rich fluid will start to excrete and push the sperm along the seminiferous tubules as it moves up towards the reti testes the cell type starts to change into more of a cilia type and this can propel it along into the epididymis at the same time as we move kind of in this region all that fluid is reabsorbed back in back into the testes and the actual ducts itself is very high and rich now with spermatozoa so this will now not so much mature with the sperm but actually not now make it motile so as we move into the epididymis what the change is in from this part into the into the more proximal part is going to be essentially the that the sperm become more motile and then when ejaculation occurs that goes up the ductus deferens up into the abdomen for ejaculation so hopefully now what you've seen is how we go from a stem cell in the embryo okay we produce the testes with the seminiferous tubules in the lobules which give you the the vast amount of volume in the in the actual testes how we go from a more of a primitive structure of the seminiferous tubules more the adult structure with particularly a strong focus on us atole cells that's supporting the suit oles are also called Sesenta killer cells which as i said it's probably the hama - the follicular cells which helps to support the germ cell and we've seen how this germ cell changes from a spermatogonia into a spermicide into a spermatid into its the Metazoa and that process all our processes for managed Ennis's but the latter process is called sperm and Genesis