Question

Shortly explain how polyspermy is blocked. which cell is reposible to do it?

Answer 1

Polyspermy means multiple sperms fertilizing a single ovum. This may happen because of number of sperms is in millions and ovum is only one. But it doesn't happen.

The fertilizable span of oocyte is 12-24 hours and that of sperm is 48-72 hours. Out of hundreds of millions sperms deposited in the vaginaa at single ejaculation, only thousand sperms get capacitated and enter the uterine tube while only 300-500 reach ovum. The acrosomal cap releases enzyme hyaluronidase which dissolve the cells of corona radiata. It also facilitates the penetration of zona pellucida. More than one sperm can penetrate zona pellucida.

Out of many sperms, one touches the oolemma and reach the cortex of ovum. The cortex secretes calcium which makes the vesicles of egg fuse with the plasma membrane and release contents into the perivitelline space and these contents inactivate the sperm binding receptors and also make zona pellucida and oolemma hard (zona reaction) and thus polyspermy is prevented.

The cell responsible for preventing polyspermy is Secondary oocyte (ovum).