Cortical reaction

Cortical reaction is a process that occurs during fertilization in the oocytes (egg cells) of many species. This reaction is triggered when a sperm makes contact with the membrane of an oocyte. The cortical reaction results in changes to the oocyte's membrane that prevent additional sperm from binding to and penetrating the oocyte. This ensures that only one sperm fertilizes the oocyte, a crucial aspect of sexual reproduction.

Mechanism

The cortical reaction begins when a sperm binds to the zona pellucida, a glycoprotein layer surrounding the oocyte. This binding triggers an increase in the concentration of calcium ions within the oocyte. The calcium ions stimulate the cortical granules, small vesicles located just beneath the oocyte's membrane, to release their contents by exocytosis.

The substances released by the cortical granules alter the properties of the zona pellucida. This alteration, known as the zona reaction, hardens the zona pellucida and removes the sperm-binding receptors, preventing additional sperm from binding to the oocyte.

Significance

The cortical reaction is a vital part of the fertilization process. By preventing polyspermy, the fertilization of an oocyte by more than one sperm, the cortical reaction ensures that the resulting embryo has the correct number of chromosomes. Polyspermy can lead to aneuploidy, an abnormal number of chromosomes that can cause developmental abnormalities or death of the embryo.

See also

• Acrosome reaction
• Capacitation
• Fertilization
• Polyspermy

References

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