Cortical reaction

Definition

The cortical reaction is a vital physiological process that occurs in the egg cell after fertilization, where cortical granules release their contents into the space between the egg membrane and the zona pellucida. This process is crucial because it prevents polyspermy, ensuring that only one sperm fertilizes the egg, and initiates changes in the egg's outer layer that protect the embryo as it begins to develop. This mechanism serves as a critical first step in the series of events leading to successful pregnancy.

5 Must Know Facts For Your Next Test

1. The cortical reaction occurs within minutes after sperm penetration and is triggered by a rise in intracellular calcium levels in the egg.
2. During the cortical reaction, enzymes released from cortical granules modify the zona pellucida to harden it, creating a barrier to additional sperm entry.
3. This reaction is essential not just for preventing polyspermy but also for initiating embryonic development processes like cleavage.
4. In mammals, the cortical reaction is part of a series of changes known as oocyte activation, which prepares the egg for successful fertilization.
5. Failure of the cortical reaction can lead to serious developmental abnormalities or embryonic failure due to polyspermy.

Review Questions

• How does the cortical reaction contribute to the prevention of polyspermy during fertilization?
  • The cortical reaction plays a crucial role in preventing polyspermy by modifying the zona pellucida after a sperm successfully enters the egg. When cortical granules release their contents, they cause biochemical changes that harden this outer layer, creating a barrier that stops other sperm from binding and penetrating. This ensures that only one sperm fertilizes the egg, which is essential for normal embryonic development.
• Discuss the significance of calcium signaling in initiating the cortical reaction and its impact on subsequent developmental processes.
  • Calcium signaling is vital for initiating the cortical reaction following fertilization. The rise in intracellular calcium levels triggers the exocytosis of cortical granules, leading to changes in the zona pellucida that prevent polyspermy. Additionally, this calcium influx activates various cellular processes necessary for early embryonic development, setting in motion critical events such as cleavage and gene activation that will shape future development.
• Evaluate how disruptions in the cortical reaction could influence reproductive success and developmental outcomes in embryos.
  • Disruptions in the cortical reaction can significantly impact reproductive success by increasing the risk of polyspermy, which often leads to developmental abnormalities or even embryo loss. If multiple sperm enter an egg due to a failed cortical reaction, it can result in incorrect genetic contributions, causing non-viable embryos. Understanding these mechanisms highlights the importance of proper cellular signaling during fertilization and underscores how failures at this early stage can have cascading effects on pregnancy and fetal health.

Related terms

zona pellucida: A thick protective layer surrounding the egg that plays an important role in fertilization and helps to prevent polyspermy.

polyspermy: A condition where an egg is fertilized by more than one sperm, which can lead to developmental issues in the embryo.

fertilization envelope: A structure formed around the egg following the cortical reaction, providing an additional barrier against multiple sperm entering.