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Fertilisation - Anatomy & Physiology (view source)
Revision as of 15:00, 3 July 2008
, 15:00, 3 July 2008→Cortical Reaction - Block to Polyspermy
== Cortical Reaction - Block to Polyspermy ==
== Cortical Reaction - Block to Polyspermy ==
* During the first and second meiotic divisions of Oogenesis small,dense '''cortical granules''' move to the periphery of the Oocyte cytoplasm.
* During the first and second meiotic divisions of Oogenesis small,dense '''cortical granules''' move to the periphery of the Oocyte cytoplasm.
* Cortical granules consist of:
** Mucopolysaccharides
** Proteases
** Peroxidase
* Cortical granules undergo '''exocytosis''', releasing their contents into the '''perivitteline space'''.
* Contents of cortical granules '''cross-links zona proteins''' to make them impenetrable to further Spermatozoa.
* This is known as the '''zona block''', it prevents polyspermy (fertilization by more than one sperm)which would result in embryo death.
* The cortical reaction also reduces the ability of the Oocyte plasma membrane to fuse with additional spermatozoa.
* This is the '''vitelline block to polyspermy'''.
* If two spermatozoa enter the perivitelline space simultaneously, they both contact the oocyte and proteins are not cross-linked rapidly enough to block penetration of the Zona Pellucida.
* Thus, the block depends on limiting the number of Spermatozoa in the vicinity of the Oocyte.
* Only a small sub-population are released from the store in the female tract over the period of ovulation so that 7-10 out of the original millions are around the Oocyte at the period of fertilization.
== Formation of Pronuclei ==
== Formation of Pronuclei ==