Difference between revisions of "Fertilisation - Anatomy & Physiology"
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== 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 == | ||
Revision as of 15:00, 3 July 2008
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.
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.
- 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.