Fertilization Process

Introduction

• Fertilization is the journey of sperm to unite with an egg, forming new human life.
• It involves a single sperm successfully reaching and penetrating the egg among many.

Initial Journey of Sperm

• Entry: During intercourse, approximately 300 million sperm enter the vagina.
• Vaginal Environment:
  • Many sperm die due to the acidic environment.
  • Protective elements in the fluid help some survive.

Passage through the Cervix

• Cervical Passage:
  • Cervix usually closed but opens during ovulation.
  • Sperm passes through thinned cervical mucus.
• Survival:
  • Many sperm die in the mucus.
  • Some sperm remain as backup in the cervix.

Journey through the Uterus

• Muscular Assistance:
  • Uterine contractions help sperm move toward the egg.
• Immune Response:
  • Immune cells destroy many sperm, mistaking them for invaders.

Fallopian Tube and Final Approach

• Direction:
  • Sperm split between empty fallopian tube and the one with the egg.
  • Few thousand sperm remain.
• Cilia and Motion:
  • Cilia in the fallopian tube push egg to the uterus, sperm must swim against it.
  • Some sperm trapped and die in cilia.
• Chemical Changes:
  • Reproductive tract chemicals alter sperm membranes, causing hyperactivity.

Reaching and Penetrating the Egg

• Corona Radiata and Zona Pellucida:
  • Sperm push through corona radiata to reach zona pellucida.
  • Acrosomes release enzymes to burrow into zona pellucida.
• Fertilization:
  • First sperm to contact the egg fertilizes it.
  • Sperm and egg membranes fuse, pulling sperm inside.

Post-Fertilization

• Prevention of Further Sperm Entry:
  • Chemical reaction prevents other sperm from attaching.
  • Zona pellucida hardens.
• Formation of Pronuclei:
  • Male genetic material forms male pronucleus with 23 chromosomes.
  • Female genetic material forms female pronucleus.
• Chromosome Fusion:
  • Microtubules bring pronuclei together forming a unique genetic code.

Conclusion

• Creation of a zygote, the first cell of a new human.
• Cilia move zygote to the uterus for implantation and development over nine months.