Cortical reaction

Definition

The cortical reaction is a crucial process that occurs in the egg immediately following fertilization, where cortical granules release their contents into the perivitelline space, leading to changes in the egg's outer membrane. This reaction serves as a protective mechanism to prevent polyspermy, ensuring that only one sperm can fertilize the egg. Additionally, it triggers various biochemical changes that activate the egg and prepare it for development.

5 Must Know Facts For Your Next Test

1. The cortical reaction is initiated when a sperm successfully fuses with the egg's plasma membrane, triggering an influx of calcium ions that stimulate the granules to exocytose.
2. One of the key outcomes of the cortical reaction is the formation of a fertilization envelope that acts as a barrier to additional sperm, preventing polyspermy.
3. In addition to blocking polyspermy, the cortical reaction also modifies the egg's extracellular matrix, ensuring that it is suitable for the developing embryo.
4. The enzymes released during the cortical reaction can also help in remodeling the zona pellucida, which is crucial for early embryo development.
5. Cortical reactions vary among species but typically involve similar mechanisms and outcomes, reflecting evolutionary adaptations in reproductive strategies.

Review Questions

• How does the cortical reaction contribute to preventing polyspermy during fertilization?
  • The cortical reaction plays a vital role in preventing polyspermy by creating a physical barrier through the formation of a fertilization envelope. When a sperm fuses with the egg, calcium ions are released, causing cortical granules to release their contents. This results in changes to the egg's outer membrane, effectively blocking other sperm from entering and ensuring that only one sperm fertilizes the egg.
• What are the biochemical changes triggered by the cortical reaction upon fertilization, and why are they important for egg activation?
  • Upon fertilization, the cortical reaction initiates a series of biochemical changes that activate the egg, preparing it for subsequent development. These changes include an increase in intracellular calcium levels and activation of specific signaling pathways. This activation is crucial as it stimulates metabolic processes necessary for early embryonic development and ensures that cellular machinery is ready to support growth.
• Evaluate the evolutionary significance of the cortical reaction in different species and how it reflects adaptations in reproductive strategies.
  • The cortical reaction demonstrates significant evolutionary adaptation across different species as it enhances reproductive success by preventing polyspermy. In aquatic environments where external fertilization is common, such as in many fish and amphibians, effective cortical reactions help ensure that eggs are only fertilized by one sperm among potentially many. This adaptation reflects evolutionary pressures favoring mechanisms that maximize embryo viability and successful development in various environmental contexts.

Related terms

polyspermy: The condition in which an egg is fertilized by more than one sperm, which can lead to abnormal development.

cortical granules: Membrane-bound organelles located just beneath the plasma membrane of the egg, containing enzymes and other substances essential for the cortical reaction.

fertilization envelope: A protective layer that forms around the egg after fertilization, created as a result of the cortical reaction to block additional sperm entry.