The Process of Fertilization
Fertilization is the fusion of the nuclei of male and female gametes to form a zygote.
It occurs in the upper part of the oviduct after copulation.
The sperms are drawn up by suction through the cervix into the uterus from where they swim up to the oviduct using their tails.
Although a single ejaculation contains millions of sperms, only one will fertilize the ovum.
As the ovum moves down the oviduct, it releases chemical substances that have to be neutralized by those produced by the acrosome before the sperm penetrates the ovum.
When the sperm comes into contact with the egg the acrosome bursts open and releases the lytic enzymes which dissolve the egg membrane.
The acrosome then turns inside out forming a fine filament that is used to penetrate the egg.
Hence, the head of the sperm enters the ovum, the tail is left outside the ovum.
The vitelline membrane undergoes a change that stops any other sperm from entering the ovum.
Once in the cytoplasm the head bursts to release the male nucleus.
The male nucleus then fuses with the female nucleus to form a diploid zygote.
After ovulation, the ovum can remain viable for 8-24 hours before it dies. However, the sperm cells can remain viable for 2-3 days within the female reproductive tract.
