Oocyte Development

Notice - Mark Hill

Currently this page is only a template and will be updated (this notice removed when completed).

Introduction

Historic drawing comparing the size of the mature human oocyte with a spermatozoa

Prior to release from the ovary oocytes (eggs, ova) are arrested at an early stage of the first meiotic division as a primary oocyte (primordial follicle). Following purberty, during each menstrual cycle, pituitary gonadotrophin stimulates completion of meiosis 1 the day before ovulation. Early oocytes are also classified as immature (germinal vesicle (GV) or metaphase I (MI) stage).

Historic Embryology - Genital
General: 1901 Urinogenital Tract \| 1902 The Uro-Genital System \| 1904 Ovary and Testis \| 1912 Urinogenital Organ Development \| 1914 External Genitalia \| 1921 Urogenital Development \| 1921 External Genital \| 1942 Sex Cords \| 1953 Germ Cells \| Historic Embryology Papers \| Historic Disclaimer
Female: 1904 Ovary and Testis \| 1904 Hymen \| 1912 Urinogenital Organ Development \| 1914 External Genitalia \| 1914 Female \| 1921 External Genital \| 1927 Female Foetus 15 cm \| 1927 Vagina \| 1932 Postnatal Ovary
Male: 1887-88 Testis \| 1904 Ovary and Testis \| 1904 Leydig Cells \| 1906 Testis vascular \| 1909 Prostate \| 1912 Prostate \| 1914 External Genitalia \| 1915 Cowper’s and Bartholin’s Glands \| 1920 Wolffian tubules \| 1935 Prepuce \| 1935 Wolffian Duct \| 1942 Sex Cords \| 1943 Testes Descent \| Historic Embryology Papers \| Historic Disclaimer

Oogenesis

A human infant ovary histology, showing the large number of oocytes occupying the ovary cortical region. Compare this with a mature ovary and note the absence of any follicle development in the infant.

The graph below shows the changes in human germ cell numbers in the ovary with age, peaking at about 7 million (occuring in early fetal development) and then decreasing by apopotic cell death. At puberty there remain only about 400,000 and only about 10% of these will be released through reproductive life. (More? Menstrual Cycle)

Graph based on data from Hassold, etal., 1996^[1]

Meiosis

In females, the total number of eggs ever to be produced are present in the newborn female.

All eggs are arrested at an early stage of the first meiotic division as a primary oocyte (primordial follicle). Following purberty, during each menstrual cycle, pituitary gonadotrophin stimulates completion of meiosis 1 the day before ovulation.
In meiosis 1, a diploid cell becomes 2 haploid (23 chromosomes) daughter cells, each chromosome has two chromatids. One cell becomes the secondary oocyte the other cell forms the first polar body.
The secondary oocyte then commences meiosis 2 which arrests at metaphase and will not continue without fertilization.
At fertilization meiosis 2 completes, forming a second polar body. Note that the first polar body may also undergo this process forming a third polar body.

Abnormalities

Trisomy 21 female karyotype

Meiotic non-disjunction resulting in aneuploidy, most are embryonic lethal and not seen. The potential for genetic abnormalities increase with maternal age.

Autosomal chromosome aneuploidy
- trisomy 21 - Down syndrome
- trisomy 18 - Edwards syndrome
- trisomy 13 - Patau syndrome

Sex chromosome aneuploidy
- monosomy X - Turner's Syndrome
- trisomy X - Triple-X syndrome
- 47 XXY - Klinefelter's Syndrome

Additional Images

Human oocyte
Human oocyte metaphase I
Human oocyte metaphase II

References

↑ <pubmed>8908177</pubmed>

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Cite this page: Hill, M.A. (2024, April 16) Embryology Oocyte Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Oocyte_Development

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[1] <pubmed>8908177</pubmed>

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