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Sperm in the Female Tract - Anatomy & Physiology (view source)
Revision as of 08:31, 8 September 2008
, 08:31, 8 September 2008no edit summary
== Penetrating the Zona Pellucida ==
== Penetrating the Zona Pellucida ==
* Spermatozoa contain zona binding proteins on their plasma membrane surfaces overlying the acrosome, which bind specifically to zona pellucida proteins (these must be exposed during capacitation before zona binding can occur).
* The zona pellucida consistes of three glycoproteins, zona proteins 1,2 and 3.
** '''Zona proteins 1&2''': structural proteins, provide structural integrity of the zona.
** '''Zona protein 3''': binds to proteins on the spermatozoal membrane.
* The sperm plasma membrane contains two zona binding sites:
** Primary zona binding region: responsible for adherence to the zona pellucida.
** Acrosome reaction promoting ligand: when this binds to the zona protein 3, signal transduction occurs to initiate the acrosome reaction.
* After the acrosome reaction, zona penetration is a rapid process (minutes).
* The acrosome reaction releases enzymes:
** '''Acrosin''': hydrolyses zona proteins and enhances the ability of sperm to bind to the zona.
** '''Proacrosin''': innactive form of acrosin with a strong affinity for the zona pellucida. It aids in binding spermatozoon to the zona as the acrosome reaction proceeds.
* As proacrosin is converted to acrosin, sperm begins to penetrate the zona pellucida.
* Sperm digest a small hole in the zona pellucida through which it can pass. This small,regional dissolution leaves the zona predominantly intact. Maintainence of the zona is important to prevent blastomeres in the early embryo from separating.
* Mechanical force generated by the flagellar action of the tail is sufficient to then push sperm through the zona.