Biology Module 3 - 3.sexual reproduction in humans 3.8 discuss how and where fertilization and implantation normally occurs

3.8 discuss how and where fertilization and implantation normally occurs

Fertilization occurs when the nucleus of a sperm fuses with the nucleus of a female gamete in the oviduct

• Semen is ejaculated into the vagina; sperm become capaciated so swim more strongly rapidly

• sperm swims towards oviducts where fertilization takes place

• receptors on cell wall surface binds to proteins in zona pellucida surrounding secondary oocyte

• a sperm digest zona pellucida and fuses with the membrane of the ovum. the zona pellucida prevents another spermatozoon from binding

• meiosis II is stimulated, the nucleus of the sperm enter the egg nuclei and fuse to form diploid nucleus

• zygote continues to divide and chorionic gonadotrophin (CG) is releases which prevents the corpus luteum from degenerating and so stimulates the corpus luteum to secrete oestrogen and progesterone which stimulate the endometrium to make it rich in blood supply

• as blastocyst is forming it slowly moves along the oviduct. movement is caused by action of the cilia on oviduct and slow steady contractions of muscles in oviduct wall

• the embryo then sinks into the endometrium (implantation) 3 or 4 days after fertilzation