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Fertilisation - Anatomy & Physiology (view source)
Revision as of 18:16, 3 July 2012
, 18:16, 3 July 2012→Syngamy
[[Image:Fertilization histology.jpg|right|thumb|250px|<small><center> Electron Scanning Micrograph of Spermatozoa in the Uterine Horn. Copyright RVC 2008 (Courtesy of John Bredl (RVC))</center></small>]]
|backcolour =EED2EE
|linkpage =Reproductive System - Anatomy & Physiology
|linktext =Reproductive System
|maplink = Reproductive System (Content Map) - Anatomy & Physiology
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== Fusion with the Oocyte ==
== 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.
* When the spermatozoon 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.
* 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 [[Copulation_-Sperm_in_the_Female_Tract_-_Anatomy_%26_Physiology|acrosome reaction]].
**Brought about by a fusion protein that is inactive prior to the [[Sperm in the Female Tract - Anatomy & Physiology|acrosome reaction]].
* Nucleus of the spermatozoon is within the oocyte cytoplasm.
* Nucleus of the spermatozoon is within the oocyte cytoplasm.
* Sperm nuclear membrane disappears.
* Sperm nuclear membrane disappears.
* Sperm '''nucleus decondenses'''.
* Sperm '''nucleus decondenses'''.
== 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:
* Cortical granules consist of:
** Mucopolysaccharides
** Mucopolysaccharides
** Peroxidase
** Peroxidase
* Cortical granules undergo '''exocytosis''', releasing their contents into the '''perivitteline space'''.
* 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.
* 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.
* 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.
* The cortical reaction also reduces the ability of the oocyte plasma membrane to fuse with additional spermatozoa.
* This is the '''vitelline block to polyspermy'''.
* 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.
* 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.
* 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.
* 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.
''N.B: Although sperm mitochondria enters the Ooctye cytoplasm, they carry a ubiquitin signal. They are subsequently destroyed by Ubiquiitinase and do NOT contribute to mitochondrial DNA. Therefore mitochondial DNA is entirely from the maternal side.''
''N.B: Although sperm mitochondria enters the Ooctye cytoplasm, they carry a ubiquitin signal. They are subsequently destroyed by Ubiquiitinase and do NOT contribute to mitochondrial DNA. Therefore mitochondial DNA is entirely from the maternal side.''
[[Category:Pregnancy and Parturition]]
[[Category:Bullet Points]]