Fertilisation - Anatomy & Physiology

Fusion with the Oocyte

• When the Spermatozoan completely penetrates the Zona Pellucida and reaches the Perivitelline Space, it settles into a bed of microvilli formed by the Oocyte plasma membrane.
• Oocyte plasma membrane fuses with the equitorial segment and the fertilizing Spermatozoon is engulfed.
  • Brought about by a fusion protein that is inactive prior to the acrosome reaction.
• Nucleus of the Spermatozoon is within the Oocyte cytoplasm.
• Sperm nuclear membrane disappears.
• Sperm nucleus decondenses.

Electron Scanning Micrograph of Spermatozoa in the Uterine Horn. Copyright RVC 2008 (Courtesy of John Bredl (RVC))

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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.