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Secondary Oocyte

Secondary Oocyte

Oocytus secundarius

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Quick Facts

A secondary oocyte is an oocyte in the period between the first and second maturation division; it is derived from a primary oocyte shortly before ovulation by a division that splits off the first polar body. If fertilized, it divides into an ootid and the second polar body; otherwise, it perishes. In humans, it is a round cell about 0.1 mm in diameter and consists of protoplasm that contains some yolk, enclosed by a thin cell wall, the vitelline membrane. It is surrounded by the zona pellucida and corona radiata (Dorland, 2011).

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Structure and/or Key Feature(s)

When the first meiotic division is completed in a mature follicle, equal share of chromatin is distributed to each daughter cell but only one receives most of the cytoplasm and becomes the secondary oocyte. It is about 150 μm in diameter. The other (diploid) daughter cell becomes the first polar body and will persist for more than 20 hours after ovulation.

The second meiotic division commences immediately after the first meiotic division is completed. As it leaves the ruptured follicle at ovulation, surrounded by the corona radiata, it is arrested at metaphase in the second meiotic division and this second meiotic division is only completed if it is penetrated by a spermatozoon (Ross and Pawlina, 2006).

For more information, check out our secondary oocyte micromodel.


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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