Sperm reach the egg through a journey involving several stages, culminating in fertilization.
The Sperm's Journey
After sexual intercourse, millions of sperm are deposited in the vagina. They then begin a trek towards the fallopian tubes, where fertilization typically occurs. This journey is challenging, with many sperm failing to reach their destination.
- Vagina to Cervix: Sperm initially navigate the acidic environment of the vagina, with many succumbing to this hostile environment.
- Cervix to Uterus: The cervix, the opening to the uterus, acts as a filter, allowing only the most motile and healthy sperm to pass through.
- Uterus to Fallopian Tubes: Sperm then swim through the uterus, guided by chemical signals, toward the fallopian tubes. This journey requires considerable energy and motility.
- Fallopian Tube Encounter: Finally, in the fallopian tubes, sperm encounter the egg (ovum), which has been released from an ovary.
Fertilization
Once a sperm successfully penetrates the egg's outer layer, fertilization takes place. The sperm's genetic material fuses with the egg's, creating a zygote – a single cell containing all the genetic information needed for a new human being. As noted in the provided video snippet, "[t]he fertilized egg then begins a rapid descent to the uterus. Over the next seven days the human embryo undergoes multiple cell divisions in a process called mitosis."
Factors Affecting Sperm-Egg Meeting
Several factors can influence the success of sperm reaching and fertilizing the egg, including:
- Sperm count and motility: A lower sperm count or reduced motility decreases the chances of fertilization.
- Ovulation timing: Sexual intercourse needs to occur around the time of ovulation (egg release) for fertilization to be possible.
- Female reproductive health: Conditions affecting the female reproductive tract can also impair sperm transport.
