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Zona Pellucida (of Tertiary Ovarian Follicle)

Zona Pellucida (of Tertiary Ovarian Follicle)

Zona pellucida folliculi ovarici tertiarii

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Quick Facts

The zona pellucida is a thick, transparent, noncellular layer or envelope of uniform thickness surrounding an oocyte. Under the light microscope, it appears as a radially striated layer (Dorland, 2011).

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Structure and/or Key Feature(s)

A zona pellucida forms around the oocyte when it is about 50-80 μm in diameter. This is a tough, eosinophilic or very pink stained, acellular, protective membrane that separates the oocyte and surrounding granulosa cells. Granulosa cells send processes inwards invading the zona pellucida, so that they can form gap junctions with the microvilli of the oocyte.

Anatomical Relations

A zona pellucida forms around the oocyte.


In the human female, the zona pellucida contains three classes of glycoproteins (ZP-1, ZP-2 and ZP-3) (Ross and Pawlina, 2006).

—ZP-1 links ZP-2 and ZP-3.

—ZP-2 is a secondary spermatozoon binding protein.

—ZP-3 is the most significant spermatozoon binding receptor and the inducer of the acrosome reaction (Ross and Pawlina, 2006).

List of Clinical Correlates

Failure of ZP-1 to function correctly results in ZP-3 accumulating in the ooplasm and no functional zona pellucida forming around the oocyte (Ross and Pawlina, 2006).


Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.

Ross, M. H. and Pawlina, W. (2006) Histology: A text and atlas. Lippincott Williams & Wilkins.

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