Cortical granules

Definition

Cortical granules are specialized secretory vesicles located in the oocyte's cortex that play a crucial role in fertilization. Upon fertilization, these granules undergo exocytosis, releasing their contents into the space between the oocyte membrane and the zona pellucida, which helps to prevent polyspermy and initiates changes in the egg's environment that are vital for successful embryo development.

5 Must Know Facts For Your Next Test

1. Cortical granules contain enzymes and other molecules that modify the zona pellucida to create a barrier against additional sperm entry after fertilization.
2. The release of contents from cortical granules occurs rapidly after sperm entry, usually within minutes, to ensure effective prevention of polyspermy.
3. Cortical granule activation is triggered by an increase in intracellular calcium levels following sperm-egg fusion.
4. The transformation of the zona pellucida into a hardened structure, known as the fertilization envelope, is facilitated by the actions of enzymes released from cortical granules.
5. In many species, including humans, the failure of cortical granule function can lead to serious reproductive issues due to increased risk of polyspermy.

Review Questions

• How do cortical granules contribute to preventing polyspermy during fertilization?
  • Cortical granules release enzymes upon fertilization that alter the zona pellucida surrounding the oocyte. This alteration creates a physical barrier known as the fertilization envelope, which prevents additional sperm from binding to and entering the egg. By ensuring that only one sperm can fertilize the egg, cortical granules play a crucial role in maintaining normal embryonic development.
• Discuss the biochemical changes that occur in the oocyte upon the release of cortical granule contents after fertilization.
  • Upon fertilization, there is a rapid increase in intracellular calcium levels that triggers exocytosis of cortical granules. The contents released include enzymes that modify the zona pellucida and create a hardened barrier. These biochemical changes ensure that once fertilization has occurred, no other sperm can enter, effectively securing the genetic material contributed by the single sperm.
• Evaluate the implications of dysfunctional cortical granules on reproductive success and embryonic development.
  • Dysfunctional cortical granules can lead to improper responses following fertilization, such as inadequate modification of the zona pellucida. This may result in polyspermy, where multiple sperm fertilize an egg, causing abnormal chromosomal content and often leading to failed embryonic development. Understanding these mechanisms is essential for addressing fertility issues and developing potential treatments for reproductive disorders related to gamete interaction.

Related terms

zona pellucida:

A glycoprotein layer surrounding the plasma membrane of an oocyte that provides structural support and plays a role in sperm binding and fertilization.

polyspermy:

A condition where an egg is fertilized by more than one sperm, which can lead to abnormal embryonic development and is prevented by mechanisms such as the cortical granule response.

exocytosis:

The process by which cells expel materials in vesicles; in the case of cortical granules, this process is critical for releasing enzymes that modify the egg's extracellular matrix after fertilization.