High Quality Content by WIKIPEDIA articles! The zona pellucida (plural zonae pellucidae) is a glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but not extraneous to it. The zona pellucida first appears in multilaminar primary oocytes.This structure binds spermatozoa, and is required to initiate the acrosome reaction. The zona glycoprotein, ZP3, is responsible for sperm binding, adhering to proteins on the sperm plasma membrane. There is evidence that ZP3 is then involved in the induction of the acrosome reaction, whereby a spermatozoon releases the contents of the acrosomal vesicle.In humans, five days after the fertilization, the blastocyst performs zona hatching; the zona pellucida degenerates and decomposes to be replaced by the underlying layer of trophoblastic cells.The zona pellucida is essential for oocyte death and fertilization.

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