Fertilization Fertilization l Occurs in the ampullary region

Fertilization

Fertilization l Occurs in the ampullary region l Ovulation takes place at the middle of the menstrual cycle l About 200 – 300 spermatozoa reach the site of fertilization

Fertilization l Fertilization is a sequence of events that begins with the contact between a sperm and a secondary oocyte and ends with the fusion of the nuclei of the sperm and ovum and the intermingling of maternal and paternal chromosomes

Phases of fertilization l Passage of sperm through corona radiata l Penetration of the zona pellucida by the sperm l Fusion of oocyte and sperm cell membrane l Completion of the second meiotic division of the secondary oocyte

Phases of fertilization l Formation of the male pronucleus l Union of male and female pronucleus l Splitting of 23 paternal and 23 maternal chromosomes l Division of cytoplasm l Formation of two celled structure called the Zygote

Results of fertilization l Restoration of diploid chromosomal number l Bi-parental inheritance l Primary sex determination l Initiation of the cleavage of the zygote

Clinical orientation l In Vitro fertilization and “embryo” transfer l Assisted in vivo fertilization

Cleavage l Two celled zygote l Mitotic divisions l Morula Inner cell mass – embryo proper l Outer cell mass – Trophoblast - Placenta l

Blastocyst formation l Morula enters the uterine cavity l Development of blastocele l Formation of blastocyst l Cells of the inner cell mass – embryoblast l Cells of the outer cell mass – trophoblast l End of first week of development l Penetration of the uterine wall

Summary of first week of development l Begins at fertilization l Several changes take place before fertilization: Gametogenesis l Formation of zygote l Cleavage l Blastocyst formation l Penetration of endometrial stroma

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