Fertilization: The Journey of Sperm to Form New Human Life

Introduction

• Fertilization is the process where a single sperm unites with an egg to create new human life.
• Approximately 300 million sperm enter the vagina during sexual intercourse.

Vagina Environment

• Millions of sperm die due to the acidic environment of the vagina.
• Protective elements in the surrounding fluid help some sperm survive.

Journey Through the Reproductive Tract

Cervix

• The cervix usually remains tightly closed but opens for a few days during ovulation.
• Sperm swim through cervical mucus, which becomes watery for easier passage.
• Many sperm die in the mucus, some remain as backups in the cervix.

Uterus

• Muscular contractions of the uterus aid the sperm's journey.
• Women’s immune system cells destroy thousands of sperm.

Fallopian Tubes

• Half the sperm head towards the empty Fallopian Tube, half towards the tube with the egg.
• Only a few thousand sperm remain by this point.
• Sperm must surge against cilia pushing the egg toward the uterus.
• Chemicals cause sperm membranes to change, making them hyperactive.
• Only a few dozen sperm reach the egg.

Penetrating the Egg

Corona Radiata

• Egg is covered with a protective layer of cells called the Corona Radiata.
• Sperm push through this layer to reach the Zona Pellucida.

Zona Pellucida

• Sperm attach to specialized receptors, triggering digestive enzymes from their acrosomes.
• These enzymes help sperm burrow into the Zona Pellucida.

Egg Cell Membrane

• First sperm to contact the egg cell membrane will fertilize the egg.
• Fusion of sperm and egg membranes prevents other sperm from attaching.
• Egg releases chemicals that create an impenetrable fertilization membrane.
• Zona Pellucida hardens, preventing other sperm from entering.

Completion of Fertilization

• Inside the egg, male genetic material forms the male pronucleus with 23 chromosomes.
• Female genetic material forms the female pronucleus with 23 chromosomes.
• Microtubules pull pronuclei together, merging chromosomes.
• A unique genetic code forms, determining characteristics such as gender, hair color, and eye color.
• The new cell, called a zygote, begins a new human life.

Journey to the Uterus

• Cilia in the Fallopian Tube sweep the zygote toward the uterus for implantation.
• The zygote will grow and mature for nine months until birth.