FERTILISATION
Fertilisation is the process of fusion of two types of gametes ( spermatozoon and ovum ) so as to form a diploid zygote.
In human beings, fertilisation is internal and takes place mostly in the ampullary - isthmic junction of the oviduct ( Fallopian tube ) .
The secretions of the female genital tract remove coating substances , deposited on the surface of the sperms particularly those on the acrosome exposing the receptor sites and activating the sperm to penetrate the ovum . This phenomenon of sperm activation is called capacitation .
The capacitated sperm undergoes acrosomal reaction and releases various chemicals contained in the acrosome . These chemicals are collectively called sperm lysins .
Acrosomal reaction , due to these plasma membrane of the sperm fuses with the plasma membrane of the secondary oocyte so that the sperm contents enter the oocyte .
Cortical reaction , after the fusion of the plasma membrane of oocyte with sperm , the cortical granules fuse with the plasma membrane releasing their contents along with cortical enzymes which hardens the zona pellucida preventing entry of additional sperms , i.e. , polyspermy .
Entry of the sperm induces the completion of the meiotic division of the secondary oocyte . The second meiotic division is also unequal and results in the formation of second polar body and a haploid ovum ( ootid ) . Haploid nucleus of the sperm and that of the ovum fuse together to form a diploid zygote.
Manish Mevada
M.Sc, M.Phil, B.Ed
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