Armando hasudnungan biology and medicine videos this video is the first part in a series of videos that will look at fertilization here we have the reproductive female organ, the uterus and the ovaries Ovaries are female gonads, and ovaries are what will produce the female egg woman go through a cycle each month called the menstrual cycle where they ovulate and release an egg this process is called ovulation, here have the secondary oocyte which is surrounded by a thick protective membrane called the zona pellucida or ZP; its filled with sperm recognition proteins called the ZP3. Surrounding the ZP is a layer of cells called the corona radiata. if this egg isn't fertilized by sperm within 24 hours, a "period occurs", or denatured endometrium slosh which looks like blood drains through the uterus into the vagina If a sperm undergoes capacitation in the vagina, and with its prepped (capacitated) acrosome (ont the tip of its head) initiates the acrosome reaction after docking with the ZP3 proteins then it will fertilize the egg the secondary oocyte will immediately undergo Mei2 forming a polar body and an Ovum, which will incorporate the sperm genes, forming a zygote on day 1 of development Remember that the ZP (zona pellucida) remains protecting the Morula and sheds later From days 2-3, Cleavage occurs. Cleavage starts with the splitting of the zygote single cell into two cells, two cells to four, four to eight, etc. The amount of cytoplasm in the dividing cell mass remains the same as the cytoplasm in the single celled zygote throughout cleavage. On day 4, the product of cleavage is a ball of 16 cells the"Morula" On day 5 the 16 cell Morula has cleaved again into a 32 cell Blastocyst. The ZP remains surrounding the blastocyst On day 7, the Zona Pellucida is shed from the 32 cell blastocyst. this happens immediately prior to implantation If you were to look at a cross section of the blastocyst just prior to implantation you would find that it is a hollow cell mass sphere with a lump of cells on the side which binds to the lining of the uterus (endometrium)