Published on December 31, 2019   53 min

Other Talks in the Series: The Female Reproductive System: from Basic Science to Fertility Treatments

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Good day, my name is Ruth Shalgi and I'm a researcher in the Department of Cell and Developmental Biology in the Sackler School of Medicine in Tel Aviv University in Israel. My research area is fertilization and the talk today will be about fertilization.
Fertilization is actually a series of coordinated and programmed processes which starts with binding of the two gametes, the sperm binds to the oocyte. But once they bind, it's not the end of fertilization as fertilization is the binding of the two genomes from the two sources. So fertilization ends when the chromosomes of the two gametes are arranged on the first mitotic spindle of the zygote, and the development of the new individual is initiated.
Let us talk a little bit on the general process of fertilization in mammals, and humans belong to mammals, they ejaculate, the sperm is deposited in the female vagina. Fertilization, it's actually internal fertilization not like in samples in the other lower species evolutionary. So the sperm are deposited in the vagina, which is, of course, in the female tract, and the sperm have to move from the area where they were deposited to the area of fertilization. Now, in the human, for example, the vagina is a very hostile area and sperm have to leave that very quickly and travel along the female tract, interacting with it, undergoing several biochemical changes until they get to the point of fertilization. At fertilization, the sex of the embryo is determined and the diploid number of chromosomes is restored. I'm just reminding you that the sperm comes along only with a haploid number of chromosomes as it underwent meiosis and it is now a haploid cell. These are the only haploid cells in the body and the female oocyte is on its way to become haploid. After fertilization, as I said, the female and the male gametes will unite on the spindle of the first mitosis and the cleaving embryo will start developing. You can see that as the oocyte ovulated, the oocyte is being fertilized in the tube, and from there, it is being pushed slowly slowly by the contraction of the muscles of the tube towards the uterus. While it's being moved by the muscles and by the cilia of the wall, the embryo will cleave, and at the end, it will come to implant as a blastocyst in the uterus. So the embryo cleaves and develops into the blastocyst, which is transferred along the tube and enters the uterus. Now, what happens if it's not fertilized? If it's not fertilized within a day, the oocyte will age, degenerate, die, and be absorbed. It's a giant cell, but it's just one cell. We will see all the stages of ovulation which were studied earlier and the sperm that are entering the oocyte, the zygote is developed, the first cleavage and then developing and implanting into the uterus.