Fertilization Process

Overview

• Fertilization is the process where a sperm and an egg unite to form new life.
• Involves a challenging journey for sperm through the female reproductive system.

Initial Entry of Sperm

• Sperm Count: About 300 million sperm enter the vagina during sexual intercourse.
• Survival Rate: Many sperm die due to the acidic environment or flow out, but some survive due to protective fluid.

Journey Through the Cervix

• Cervix Function: Normally closed but opens during ovulation, allowing sperm to enter.
• Cervical Mucus: Sperm must swim through a viscous mucus to reach the uterus.
• Challenges: Many sperm die or get stuck in the cervix.

Movement to the Uterus

• Muscular Contractions: Facilitate sperm movement towards the egg.
• Immune Response: Female immune cells may mistakenly attack sperm.
• Pathways: Half of the sperm go into empty fallopian tubes; the other half head towards the tube with the egg.

Inside the Fallopian Tube

• Cilia Action: Small cilia push the egg towards the uterus.
• Sperm Location: Only a few thousand sperm remain in the fallopian tube.
• Chemical Changes: Chemicals in the reproductive tract activate sperm, making them swim faster.

Final Approach to the Egg

• Remaining Sperm: A few dozen sperm reach the egg after overcoming all obstacles.
• Zona Pellucida: An outer layer of the egg that allows only one sperm to penetrate.
• Fertilization Event: The first sperm to reach the egg's ovular membrane fuses with it.

Fertilization Mechanics

• Preventing Further Entry: The egg’s membrane changes to repel other sperm after one fertilizes it.
• Genetic Material: Male genetic material forms a male pronucleus with 23 chromosomes.
• Female Pronucleus Formation: Female genetic material completes division and forms a female pronucleus.

Completion of Fertilization

• Microtubules Role: Pull male and female pronuclei together, uniting chromosomes.
• Unique Genetic Code: The fertilized egg (zygote) has a unique genetic code dictating characteristics.

Development Post-Fertilization

• Zygote Formation: The single-celled zygote begins the journey of development.
• Implantation: Zygote is swept into the uterus to implant into the uterine walls, beginning nine months of growth until birth.