Zona pellucida

The zona pellucida is a thick, protective layer surrounding an egg (oocyte) in the ovary. This glycoprotein shell plays a crucial role in reproduction by facilitating sperm binding and ensuring that only one sperm can penetrate to fertilize the egg. Once fertilization occurs, the zona pellucida undergoes changes to prevent additional sperm from entering. It also helps in the early stages of embryo development by providing a barrier and supporting the embryo as it moves to the uterus. Overall, the zona pellucida is essential for successful fertilization and early embryonic development.