8 lecture 6 is on the ovaries and oogenesis in the ovaries there are several different layers in there the very outside is the germinal epithelium and then beneath that we have the tunica albigenia just like we did with the testes and the penis then there's the cortex and the medulla remember cortex is always external medulla is always internal the cortex is where we find the ovarian follicles and the medulla is where we have the blood vessels lymphatics and nerves that service the ovaries so the follicles consist of oocytes that are in different stages of development when they mature they're called graphene follicles and a graphene follicle is going to have a mature oocyte a secondary oocyte in it and it's going to expel that into or i should say out of the ovary through a process called ovulation what remains of that follicle is called the corpus luteum and it's going to produce progesterone estrogens relaxin and inhibin if pregnancy doesn't occur then it's going to degenerate into corpus albicans and the corpus albicans is basically scar tissue so for every time a woman ovulates there's scar tissue for from that oocyte that was expelled on her ovary you can actually if you look at older women's ovaries you can actually tell them fairly easily from a younger woman simply because of all of the scar tissue on them from ovulation so this is showing here's the medulla and this is where the blood vessels go in the outer area here is the cortex the dermal epithelium covers it and in the cortex we have oocytes in follicles at different stages of development so the follicle has to develop as well as the oocyte within it you can think of the follicles sort of being like an incubator to produce the um mature oocyte but the follicle also has the job of helping to produce hormones so um the tunic albigenia is dense connective tissue cortex uh contains the follicles medulla has all the connective tissue blood vessels and lymphatics and the germinal epithelium is just epithelium covering the ovary oogenesis occurs in the ovary and it is the formation of a single haploid secondary oocyte remember haploid means it's going to have half of the genetic material of all the other cells in the female body so that when this haploid oocyte combines with a haploid sperm cell we're now going to have a diploid individual so this includes reduction division which is meiosis 1 and equatorial division which is meiosis 2 and then maturation so while oogenesis is going on the follicles are also undergoing developmental changes and the changes they go through start at primordial primary secondary and mature or gravy and follicle and then that's followed first actually by the corpus hemorrhagicum which is where it's sort of after following ovulation it's sort of bloody and then the corpus luteum and then the corpus albicans and here you can see this is the corpus hemorrhagicum um when ovulation occurs it actually tears through the wall it isn't like it's released through exocytosis or something like that it actually makes a hole through the wall and that's why you end up with scar tissue afterwards so the corpus luteum is an ovulation wound and it fills in with hormone secreting cells and the corpus albicans is a scar an ovarian cyst is a common occurrence in women and it's a cyst just means a fluid-filled sac most women as they age are going to have some fibroids they're going to have some cysts it's normal and generally unless it becomes a real problem it doesn't require surgery or any other treatment so a graphene follicle this remembers the mature follicle has several uh regions to it there's the zona pellucida and that's pellucida lucid clear so it's a clear area between the oocyte and the granulosa cells around it the corona radiata this is where the granulosa cells attach to the zona pellucida and the antrum this is the area that's filled with fluid surrounding the granulosa cells by the time an oocyte is ready to be reached reaches the period where it's ready to be take part in ovulation it reaches metaphase meiosis ii now unlike the sperm that completes meiosis ii and you end up with four sperm cells with ovulation we're releasing polar bodies and polar bodies are a way to get rid of the excess dna so that you end up with one egg at the end but the oocyte the secondary oocyte has not completed meiosis ii and it will not complete meiosis ii until it's fertilized if it's not fertilized it never completes meiosis ii so basically it's gone through meiosis one it's gotten rid of half of the dna through one polar body then it starts meiosis ii and it arrests at metaphase metaphase is when they line up down the center and the chromosomes line up down the center of the cell and it stays at metaphase until it's fertilized when it's fertilized the first thing that happens is it completes meiosis ii gives off that second polar body and then the male and female pro nuclei fuse and we have the new individual germ cells from the yolk sac and we're talking in a female fetus they migrate to the ovary and become the oegonia these are the counterpart of the spermatogonia in the female fetus these are going to divide produce millions of cells by mitosis but most of these are going to degenerate and their degeneration is called atresia some of them are going to develop into primary oocytes and they stop at prophase stage of meiosis one so prophase this is when the nucleus disappears and you first start seeing chromosomes so there's been no division that takes place it's just you have the formation of chromosomes and they're ready to to go by the time a woman is born she has already made all the eggs she ever will there's 200 000 to 2 million of these and 40 000 of them are going to be still be there by puberty the rest will have degenerated through atresia but during a woman's lifetime only 400 of those 40 000 will mature so each month hormones are going to cause meiosis one to resume so then it's going to go from prophase to metaphase to anaphase to telophase to cytokinesis and then you're going to create that first polar body and get rid of it and then it's going to start to go through meiosis ii and it will rest at metaphase and this happens in several follicles again penetration by the sperm causes the final stage of meiosis