Fertilization
is a natural biological process in which male and female gametes fuse to
generate a zygote. During coitus, thousands of sperms are inseminated into the
female vagina. Although all these sperms travel to the fallopian tube, only a very
small percentage make their way there. The fallopian tube is where the eggs are
fertilized. The secondary oocyte exits the ovary's mature graafian follicle and
enters the fallopian tube, where it is fertilized within 24 hours before being
released.
The oocyte
is fertilized by a single sperm, although it may be surrounded by many. The
sperm enters the secondary oocyte during meiosis-II, which completes the
meiosis process. The egg is the name given to the second oocyte after that.
Both sperm and eggs have a limited time to exhibit their viability. In the female
reproductive system, the sperm may survive for 48-72 hours, whereas an egg can
be fertilized for up to 24 hours before being released.
Binding of
the egg and sperm can also be done in the lab. This is made possible using
Assisted Reproductive Technology (ART), namely the In Vitro Fertilization (IVF)
method, and is considered as a viable process of fertilization.
Process of Fertilization
The process
of fertilization is divided into three primary stages.
Chemotaxis, Acrosomal reaction (sperm activation) and Adhesion of sperm to
eggs.
Women ovulate once a month during the menstrual cycle, which plays a key role in conception. When this cycle releases an egg cell from the ovaries, the first step of fertilization begins. When a sperm encounters an oocyte, it binds to the zona pellucida, which is a thick coating of a jelly-like extracellular matrix made up of glycoproteins that surrounds the egg. When a particular molecule on the sperm's surface binds to a ZP3 glycoprotein in the zona pellucida, the acrosome reaction is started. Hyaluronidase is produced by the acrosome process, and it ferments the hyaluronic acid surrounding the egg, allowing the sperm to pass through.
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Following
successful sperm implantation, the egg's cortical granules fuse with the cell's
plasma membrane and are discharged into the zona pellucida, causing the surface
to become stiff and impervious. The cortical response guarantees that just one
sperm cell enters the egg and fertilizes it.
Once the
sperm has successfully reached the egg, the outer coating and tail of the sperm
disintegrate. The oocyte goes through meiosis to become a haploid ovum. The
genetic material of sperm and egg, each of which has 23 chromosomes, is merged,
resulting in a diploid cell with 46 chromosomes, called as a zygote. The zygote
then undergoes mitosis, which is the repeated cellular division essential for
an organism's growth, to generate a blastocyst. This is then implanted into the
uterine wall, initiating the pregnancy.
If you have more questions about the process of fertilization, you can consult a gynecologist. You can also ask about the IVF method. Even the best pediatricians in Hyderabad say that this method has successfully resulted in healthy babies.
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