Definition

1. Noun:
   • A thick, transparent membrane surrounding the mammalian ovum (egg cell): The zona pellucida is a glycoprotein layer that encloses the oocyte and the early embryo.
   • A structure involved in fertilization and early embryonic development: It acts as a selective barrier, allowing only one sperm to penetrate during fertilization and protecting the developing embryo until implantation.

Usage Examples

• Noun:
  • The sperm must first bind to and penetrate the zona pellucida to fertilize the egg.
  • After fertilization, the zona pellucida undergoes changes to prevent additional sperm from entering.
  • The embryo hatches from the zona pellucida before it can implant in the uterine wall.

Advanced Usage

• "Zona pellucida hardening": A process, often induced in vitro, that makes the membrane less permeable, sometimes used to prevent polyspermy (fertilization by multiple sperm).
  • Laboratory techniques sometimes involve zona pellucida hardening to improve embryonic development rates.
• "Zona pellucida drilling": A micromanipulation technique used in assisted reproductive technology (ART) to create an opening in the membrane.
  • Zona pellucida drilling can assist sperm entry in cases of male infertility.

Variants and Related Words

• Zona (n): Often used informally as a shortened form of "zona pellucida" in embryology contexts.
  • The zona must be breached for fertilization to occur.
• Pellucid zone: An alternative, less common term with the same meaning.
• ZP proteins: Refers to the specific glycoproteins (ZP1, ZP2, ZP3, ZP4) that constitute the structure of the zona pellucida.

Synonyms

• Oolemma (Note: This is not a perfect synonym. The oolemma is the egg's plasma membrane the zona pellucida, while the zona pellucida is an extracellular matrix.)
• Egg coat: A general, non-technical term for protective layers around an egg cell.

Related Phrases and Concepts

• Zona reaction: The biochemical change in the zona pellucida after the first sperm penetrates, making it impermeable to other sperm.
  • The zona reaction is a crucial block to polyspermy.
• Assisted hatching: An ART procedure where the zona pellucida is thinned or opened to help the embryo hatch.
  • Assisted hatching may be recommended for embryos with a thick zona pellucida.

Noun

1. thick membrane around the mammalian ovum; can be penetrated by one sperm in the fertilization process; usually remains around the fertilized egg until it is implanted in the wall of the uterus