hi everybody and welcome back today we are going to be doing gametogenesis and specifically we're going to focus on spermatogenesis which is the creation of sperm cells now it's really important that you have familiarized yourself with all of the structures in the male reproductive system but i'm going to go over some really important structures you need to know and along with their functions starting in the testes now there are some key features that we need to look at so in front of us in the diagram here we have the testis and then sitting inside the testers is these seminiferous tubules and these are the tubes where sperm cells are actually created then sitting just behind that where all the tubes drain into is something called the epididymis the epididymis is where we mature our sperm cells and they're stored until they are needed and finally we have what we call the ductus vas deferens or i just call it the vas deferens and you can do the same it's the tube that leaves the testes and takes the sperm cells with it now it's important to keep a couple of the following things in mind now it's important to remember that the testes are outside of the body because sperm cells are made out of protein and they can denature and they're very sensitive and so they need to be a slightly cooler temperature than the human body itself so we find the testes on the outside and that is the function of the scrotum which we can't see in this picture here considering that we are only looking at the internal structures of the testes themselves now let's take a look inside the seminiferous tubules themselves the site essentially where we actually make these sperm cells so in the diagram that you can see in front of you what they've done is that they have cross-sectioned a whole bunch of seminiferous tubules so we can see inside them and what we're going to do is we're going to look at the specific structures that you can see so we're going to zoom in even closer so we can see more specifics and starting on the outside sitting around our seminiferous tubules we have the lydic cell sitting a little further in and physically now inside the actual seminiferous tubule is something called a setoli cell and a sertone cell is essentially like a nutritive cell it's a cell whose main responsibility is to look after the developing sperm cells to provide them a place to mature and to grow bigger because when we first make sperm cells they're very small and they're underdeveloped which we'll see in the next slide as we go through their maturation and development and then you see something called germ cells and you'll see that it starts off with the baseline or this is what we also call the basement membrane the furthest out layer and you'll see that the germinal cells progress and essentially they are moving from the wall inwards and as they do so they develop and they go through stages of mitosis and meiosis which i'll do in the next slide so that you can see that but essentially a germ cell is a cell that is able to grow into a limited variety of cells in particular these germ cells are going to be turning into sperm cells and please don't confuse germ cells with stem cells their origins are not the same and their products are not the same either so let's take a look at the growth and maturation of these sperm cells and our sperm cells go through some major developments through the course of their existence starting off with what we call spermatogonia which is essentially a undeveloped undivided still diploid cell and this cell hasn't completed any of the growth or changes that we needed to do so generally in this first section over here our cell is going through mitosis it is moving through general growth and getting bigger now once the cell has reached a big enough size and it's gone through mitosis it now needs to enter into meiosis which we've already learned is when you take a full set of chromosomes and you want to half it and you want to introduce genetic variation and this takes place in this central area here and so when we go through our two separate stages of meiosis 1 and meiosis 2 we ultimately want to half the chromosomes keeping in mind that in the very beginning we were 2 n which represents a diploid structure and now we want to make cells that are just n which means that they have half the number of chromosomes remember meiosis one is where we half the chromosome number meiosis ii is when we separate the chromatids from one another and then at the very end of asthmatogenesis and growing we end up with our matured sperm cells it's also important to know that mitosis takes place here as well because at the end of meiosis ii we don't actually have a sperm cell yet we still need to go through mitosis and essentially we're not making more cells what we're actually doing is we're growing the cell we're going to allow the cell to grow bigger it's going to mature it's going to get a tail it's going to develop its mitochondria and if we have a look alongside the major events we also need to make sure that our sperm cells that we produce have certain structures they need to have a head a midpiece and a tail now the lifespan of spermatozoa which is just the formal word for sperm is that um they're made every day and millions are made every day however there is a turnover rate of around several months in other words you can store sperm cells for up to seven months but they're replaced on a daily basis slowly but surely now what governs this entire growth and maturation process well that is hormones and these hormones are secreted just before and during puberty and that's when spermatogenesis actually begins in males now the two hormones that we need to be familiar with are icsh or interstitial cell stimulating hormone and yes you can use the abbreviation and essentially icsh stimulates the testes to produce testosterone now testosterone is then secreted and one of the functions of testosterone is to produce sperm cells and so that's what starts this entire growth and maturation point when males go into puberty and you will need to know the names of these hormones and what they do lastly we need to look at a sperm cell structure and you should be able to draw or label this in a test and exam so let's go through the structures and just recap what each of these do so the acrosome is an organelle that contains digestive enzymes and the reason for the digestive enzymes is because we need to break down the eggs membrane when the sperm cells are burring into the egg they need to be able to get into the nucleus of the egg itself and introduce its dna and so that's what the acrosome does then that brings me on to the nucleus now of course we know the nucleus is where we find all of our genetic information and let's remember that this nucleus is in which means that it is haploid it has half the set of chromosomes that you would normally find in a cell we then have our centrioles which are left over from our meiotic and meiosis processes of separating cells and then we have lots and lots and lots of mitochondria we need this many mitochondria because they provide energy for the sperm cell to move now what's interesting about our mitochondria that we find in sperm cells is that they are there to provide energy for locomotion as we know sperm cells swim but the mitochondria never enters the egg cell even though the sperm cell burrows in to the egg cell in actual fact the only part of the sperm cell that actually manages to make it into the egg itself is the head of the sperm cell which contains the nucleus and this is actually proof and evidence of our evolution particularly where and from what region we have evolved from and all of us today have the same mitochondria we call it um mitochondrial descent and essentially what it means is that every single human on this planet has the same mitochondrial information that we've all inherited from an individual we call mitochondrial eve and finally we have the axial filament also known as our tail and it propels our sperm cell in a propeller-like fashion which means that the sperm cell doesn't actually wiggle from left to right in actual fact if you look at the sperm's tail when it moves it's like a propeller and it does a twisting action forwards all right to end our lesson let's do a terminology recap so we looked at spermatogenesis today which is the generation of sperm cells and sperm cells are made in the seminiferous tubules inside of the testes now in order to start this whole process an individual must be going through puberty and to start a hormone called icsh is secreted to the testes once the testes receive this hormonal message they start to produce the hormone testosterone and testosterone is vital in production of sperm and the maturation of sperm so in other words we can't actually do somatogenesis without icsh starting the process at the beginning of puberty and testosterone actually allowing us to grow the sperm cells we then have the lydex cell and the cells of setoli which are both sets of cells are used to grow and mature and look after our little baby sperm cells before they are fully grown we also looked at the words diploid and haploid which if you remember refers to the amount of chromosomes the cell has remember at the beginning of spermatogenesis the cell will have a diploid number of chromosomes in other words a full set at the end of meiosis ii we will have a haploid set of chromosomes which is what we want because remember we want to half the chromosome number because eventually we're going to take a sperm cell and an egg cell put them together and we want a full set of chromosomes not too many not too few we also learned the word spermatozoa which is the more biological word for sperm and we often shorten it down to just the word sperm and last but not least the new word we learned today was the acrosome the acrosome is a organelle that contains digestive enzymes that allows us to break down into the egg cell so that fertilization can take place yet again i hope that this video has helped you to understand and unpack the ideas please use it as a way to revise and i'm going to be making another video that will be coming up next on ogenesis and then a separate video on the menstrual cycle because both of these things need to be explained in a lot of detail and i will see you all again soon bye