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Fertilization And Implantation

Fertilization And Implantation Fertilization (Occurs in the ampulla of fallopian tube): 1. Sperm reaches the egg: After ejaculation, sperm travel through the cervix, uterus, and into the fallopian tube where the egg is waiting. 2. Zona Pellucida attracts sperm: The zona pellucida, a glycoprotein layer surrounding the egg, attracts sperm through chemical signals. 3. Acrosomal reaction: When a sperm binds to the zona pellucida, it triggers the acrosomal reaction. The acrosome (a cap-like structure on the sperm head) releases enzymes that help digest and penetrate the zona. 4. Penetration of egg by sperm: One sperm successfully penetrates the zona pellucida and fuses with the egg's plasma membrane. 5. Cortical reaction: The egg releases cortical granules into the space between the egg membrane and zona pellucida, causing biochemical changes. 6. Zona reaction: These changes harden the zona pellucida to prevent entry of other sperm (polyspermy). 7. Zygote formation: The sperm's nucleus fuses with the egg's nucleus, forming a diploid zygote (46 chromosomes). Early Embryonic Development: 8. Cleavage (Mitotic divisions): The zygote starts dividing by mitosis without growing in size. 9. Two-cell stage: About 30 hours after fertilization, the zygote divides into two identical blastomeres. 10. Morula formation: After several divisions, a solid ball of 16–32 cells forms, called the morula. 11. Blastocyst formation: Fluid enters the morula forming a hollow cavity, now called a blastocyst (contains inner cell mass and trophoblast). Implantation: 12. Begins on day 4 or 5: The blastocyst reaches the uterus around day 4–5 and starts interacting with the endometrial lining. 13. Trophoblast attachment: The trophoblast (outer cell layer) attaches to the endometrium and begins invading it. 14. Completed by second week: Full implantation is usually complete by the end of the second week after fertilization, with the blastocyst embedded in the uterine canity in the anterior or posterior wall How life begins?The beginning of life #science #facts#embryology#pregnancy