Zona pellucida

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The zona pellucida (Latin meaning "transparent zone") is the specialized area surrounding the mammalian egg cell. It is also known as an egg coat. The zona pellucida is formed in early oogenesis and is essential for oocyte growth and fertilization. In other vertebrates it is called the vitelline membrane, or the vitelline envelope in invertebrates. The zona pellucida is an extracellular matrix that surrounds the plasma membrane of the egg cell. It helps protect the egg, and has an essential role in fertilization by sperm. It is surrounded by the corona radiata. The corona is composed of cells that cared for the pre-ovulatory egg cell, and stays with the egg cell when it is emitted from the ovary.

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