Protection of female gametes from male gametes

Question

Explain, how the male gametes go through the egg cell? How the female gametes guard itself from entry of more gametes after the first sperm cell?

Answer 1

Sperm cell which reaches the egg cell activates the acrosome reaction, a procedure where the hydrolytic enzymes of the acrosome are liberated on the external surface of zona pellucida (a protective layer that surrounds the egg cell). Portion of this layer is digested by acrosomal enzymes offering the sperm cell to arrive at the plasma membrane of the egg cell performing the fecundation.

At the moment, that sperm cell forms the contact with egg cell membrane a chemical alteration of this membrane takes place. Enzymes liberated by the exocytosis form the zona pellucida not capable to bind to other sperm cells and other male gametes are not able to enter the egg cell.