Prab at 01:42, 18 November 2020

2020-11-18T01:42:31Z

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Zona pellucida is a thick, gel-like glycoprotein membrane that coats the [[oocyte]] and must be penetrated by [[sperm]] before [[fertilization]] can occur.
[[File:Zona Pellucida.png|alt=Zona Pellucida|thumb|Zona Pellucida]]

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==Ovarian follicle development==
* An ovarian follicle consists of a developing oocyte surrounded by one or more layers of cells called follicular cells.
* At the same time that the oocyte is progressing through meiosis, corresponding changes are taking place in the follicular cells.
* Primordial follicles, which consist of a primary oocyte surrounded by a single layer of flattened cells, develop in the fetus and are the stage that is present in the ovaries at birth and throughout childhood.
[[File:Zona pellucida.jpg|alt=Zona pellucida|thumb|Zona pellucida]]
==Structure of an ovary==
* Beginning at puberty, follicle-stimulating hormone stimulates changes in the primordial follicles.
* The follicular cells become cuboidal, the primary oocyte enlarges, and it is now a primary follicle.
* The follicles continue to grow under the influence of follicle-stimulating hormone, and the follicular cells proliferate to form several layers of granulose cells around the primary oocyte.
* Most of these primary follicles degenerate along with the primary oocytes within them, but usually one continues to develop each month.
* The granulosa cells start secreting estrogen and a cavity, or antrum, forms within the follicle.
* When the antrum starts to develop, the follicle becomes a secondary follicle.
* The granulose cells also secrete a glycoprotein substance that forms a clear membrane, the '''zona pellucida''', around the [[oocyte]].
* After about 10 days of growth the follicle is a mature vesicular (graafian) follicle, which forms a "blister" on the surface of the ovary and contains a secondary oocyte ready for ovulation.
[[File:Oocyte with Zona pellucida (27771482282).jpg|alt=Oocyte with Zona pellucida|thumb|Oocyte with Zona pellucida]]

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==Ovulation==
* Ovulation, prompted by [[luteinizing hormone]](LH) from the [[anterior pituitary]], occurs when the mature follicle at the surface of the [[ovary]] ruptures and releases the secondary oocyte into the peritoneal cavity.
* The ovulated secondary oocyte, ready for fertilization is still surrounded by the zona pellucida and a few layers of cells called the [[corona radiata]].
* If it is not fertilized, the secondary oocyte degenerates in a couple of days.
* If a sperm passes through the corona radiata and zona pellucida and enters the cytoplasm of the secondary oocyte, the second meiotic division resumes to form a polar body and a mature ovum

==Corpus luteum==
* After ovulation and in response to luteinizing hormone, the portion of the follicle that remains in the ovary enlarges and is transformed into a [[corpus luteum]].
* The corpus luteum is a glandular structure that secretes [[progesterone]] and some [[estrogen]].
* Its fate depends on whether [[fertilization]] occurs.
* If fertilization does not take place, the corpus luteum remains functional for about 10 days; then it begins to degenerate into a corpus albicans, which is primarily scar tissue, and its hormone output ceases.
* If fertilization occurs, the corpus luteum persists and continues its hormone functions until the placenta develops sufficiently to secrete the necessary hormones.
* The corpus luteum ultimately degenerates into corpus albicans, but it remains functional for a longer period of time.

{{Female reproductive system}}
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[[Category:Germ cell structures]]
[[Category:Reproductive system]]
[[Category:Vertebrate developmental biology]]

Zona pellucida - Revision history

Prab at 01:42, 18 November 2020