What is Zona Reaction.

The Zona Reaction, also known as the cortical reaction, is a process that occurs in the egg (oocyte) during fertilization. This reaction plays a critical role in preventing polyspermy, which is the fertilization of an egg by multiple sperm cells. Here's how the zona reaction works:

Sperm Entry: When a sperm cell successfully penetrates the zona pellucida (a protective layer around the egg) and enters the egg, it triggers a cascade of events.

Cortical Granule Release: The entry of the sperm causes the egg to release cortical granules, which are specialized vesicles, from its cortical region (outer layer).

Chemical Changes: These cortical granules release their contents (enzymes and other substances) into the space between the egg and the zona pellucida.

Zona Pellucida Hardening: The enzymes released from the cortical granules modify the zona pellucida, hardening it and making it impermeable to additional sperm.

Prevention of Polyspermy: By hardening the zona pellucida and altering its structure, the zona reaction prevents any other sperm from penetrating the egg.

The zona reaction is a crucial step in ensuring that the fertilized egg develops normally, as polyspermy can lead to an abnormal number of chromosomes and developmental issues.