Cortical Reaction

Definition

The cortical reaction is a crucial biochemical response that occurs in the egg cell after fertilization, preventing polyspermy by altering the egg's outer membrane. This reaction involves the release of cortical granules, which causes a change in the zona pellucida, making it impermeable to additional sperm. This mechanism ensures that only one sperm can fertilize the egg, which is vital for successful embryonic development.

5 Must Know Facts For Your Next Test

1. The cortical reaction begins immediately after a sperm successfully penetrates the egg's plasma membrane.
2. Enzymes released from cortical granules modify the zona pellucida to create a fertilization envelope that blocks additional sperm entry.
3. This reaction not only prevents polyspermy but also activates the egg's metabolism and prepares it for the first cell division.
4. The cortical reaction is a well-coordinated process involving calcium ion influx, which triggers the granule exocytosis.
5. In many species, including humans, failure of the cortical reaction can lead to developmental defects or complete failure of embryo development.

Review Questions

• How does the cortical reaction prevent polyspermy after fertilization?
  • The cortical reaction prevents polyspermy by initiating a series of changes in the egg's outer layer once a sperm penetrates its membrane. Upon fertilization, cortical granules release their contents, modifying the zona pellucida and making it impermeable to other sperm. This transformation creates a barrier that ensures that only one sperm can fertilize the egg, which is crucial for proper embryonic development.
• Discuss the role of calcium ions in the process of the cortical reaction.
  • Calcium ions play a pivotal role in the cortical reaction by acting as secondary messengers that trigger exocytosis of the cortical granules. When a sperm enters the egg, there is an influx of calcium ions that initiates this biochemical cascade. The increased intracellular calcium concentration leads to the release of enzymes from these granules, which ultimately modifies the zona pellucida and contributes to preventing polyspermy while also activating developmental processes within the egg.
• Evaluate how abnormalities in the cortical reaction might impact early embryonic development and reproductive success.
  • Abnormalities in the cortical reaction can significantly impact early embryonic development by increasing the risk of polyspermy, where multiple sperm fertilize an egg. This can result in abnormal chromosomal numbers and developmental defects, ultimately leading to embryo failure or miscarriage. In cases where polyspermy is not prevented effectively due to dysfunctional cortical reactions, reproductive success is severely compromised, highlighting the importance of this mechanism in ensuring healthy development and successful fertilization outcomes.

Related terms

Polyspermy: A condition where an egg is fertilized by more than one sperm, which can lead to abnormal development.

Cortical Granules: Membrane-bound vesicles found in the egg's cytoplasm that release enzymes during the cortical reaction.

Zona Pellucida: The thick, transparent membrane surrounding the mammalian oocyte, which plays a key role in fertilization.