The
Reproductive System of a woman
The
Menstrual Cycle
The
Hormones
The
Reproductive System of a Man
The
Role of Testosterone
The
Sperm's Odyssey in the Female Reproductive Tract
The Process
of Fertilisation
The Process of
Fertilisation
Of the few hundred sperm which reach
the egg, only one will successfully fertilise it. The process of fertilisation
is truly the primeval mating dance - the fertilisation tango - when the
mother's chromosomes (in the egg) and the father's chromosomes (in the
sperm) fuse together to create a new life - one which is totally different
from all others, because of its unique genetic composition. We have now
learnt quite a lot about fertilisation thanks to in vitro fertilisation
(IVF) - and it is truly one of Nature's miracles.
During the time the sperm spend in
the female reproductive tract, while swimming towards the egg, they acquire
the capacity to fertilise it - a process called capacitation. When the
sperms reach the corona cells (only a few hundred successfully make the
trip, guided by chemicals produced by the egg which serve as guiding beacons
to the sperms) they become hyperactivated - they start beating their tails
in a frenzy. This is useful because it provides the mechanical energy the
sperm head needs to burrow its way through the outer shell of the egg called
the zona. The sperms disperse the cumulus oophorus (and so far it's a team
effort ) and when they reach the egg, they first bind to the zona. A chemical
is released here by the sperms in a process called the acrosomal reaction
in which the acrosome (which sits like a cap on the head of the sperm and
behaves much like a battering ram) is removed. The acrosomal enzymes dissolve
the zona pellucida by making a tiny hole in it, so that one sperm can swim
through and reach the surface of the egg. At this time, the egg transforms
the zona to an impenetrable barrier, thus preventing other sperm from entering
it.
The genetic material of the sperm
(the male pronucleus) and the genetic material of the egg (the female pronucleus)
then fuse - to form an embryo, which then divides into 2 cells. These cells
in turn then continue to divide rapidly, producing a ball of cells - the
embryo. The embryo then travels through the fallopian tube (which nurtures
it and propels it ) into the uterus - a journey which takes about 3 to
5 days. The embryo must then break through its zona ( this is called embryo
hatching); and then attach itself to the lining of the uterus in a process
called implantation - and in 9 months, if all goes well, a baby is born.
