Fertilization And Implantation: How & When Do They Occur?
During ovulation that happens normally in the middle of menstrual cycle an ovary releases an ovum that travels to the end of Fallopian tube, waiting for fertilization.
Fertilization occurs in Fallopian tubes. Normally only 200-300 sperm cells reach this place, because cervical mucus works as a filter, letting only agile and healthy spermatozoa continue their way up. The most persistent sperm cells have a goal to meet the ovum and pass the 2 zones surrounding it. As soon as the fastest sperm cell completes the task, the ovum changes the structure of the last zone so that no other spermatozoon can pass the barrier. Thus, a zygote is formed, completing the fertilization process.
The fertilized egg now gets new programs to acomplish: continuous division and movement towards the womb. Special cilia, covering Fallopian tubes from inside, roll the egg like a ball. Approximately by the 4th day of such a journey the egg reaches the uterine cavity. On the 5-6th day it releases itself from the surrounding membrane. Blastocyst implantation starts on the 7-9th day.