Zona pellucida

Definition

The zona pellucida is a glycoprotein layer surrounding the plasma membrane of mammalian oocytes. It plays a crucial role in fertilization and early embryonic development.

5 Must Know Facts For Your Next Test

1. The zona pellucida facilitates sperm binding and prevents polyspermy, ensuring only one sperm fertilizes the egg.
2. It is composed mainly of three or four glycoproteins, commonly referred to as ZP1, ZP2, ZP3, and sometimes ZP4.
3. During fertilization, enzymes from the sperm's acrosome react with the zona pellucida to allow sperm entry.
4. Once fertilization occurs, the zona pellucida hardens to block additional sperm from entering the egg.
5. The breakdown of the zona pellucida is necessary for implantation of the blastocyst into the uterine wall.

Review Questions

• What primary function does the zona pellucida serve during fertilization?
• Which glycoproteins are integral components of the zona pellucida?
• How does the zona pellucida prevent polyspermy after an egg has been fertilized?

Related terms

spermatozoon: A mature male gamete or reproductive cell involved in sexual reproduction.

acrosome: A cap-like structure over the anterior half of a sperm's head that contains enzymes crucial for penetrating the egg's outer layers.

blastocyst: An early stage embryo consisting of an inner cell mass, which will develop into a fetus, and an outer layer called trophoblast that will form part of the placenta.