Fertilization
Once ovulation occurs, if sperm are present, they will migrate from the cervical crypts toward the fallopian tubes. Fertilization occurs just above the fimbriated end of the fallopian tube. The sperm meet the ovum and attach themselves to the cell membrane. This membrane, called the zona pellicuda, has a hard surface. The first sperm that burrows its head through this membrane creates a reaction which seals off further penetration by other sperm. The sperm leaves behind its tail, as the source of locomotion no longer needed.
Once the chromosomal material contained in the head of the sperm unites with the chromosomal material of the ovum, fertilization is complete. The fertilized ovum now begins to divide.
The fertilized ovum, known as a zygote, travels through the fallopian tube as it divides and grows. Within 3-4 days it reaches the junction of the fallopian tube and the uterine cavity. By then it will consist of 16 cells, and is known as a morula. It will then drift about in the uterine cavity for about 3-4 more days during which time it changes into a blastocyst. Then it is ready to implant onto the endometrium, where it will establish its placental life support system from the woman. Implantation takes place 6-8 days following fertilization.
If fertilization does not occur the ovum will disintegrate and die within the fallopian tube.
