Oocyte Development
Introduction
--Mark Hill 10:32, 13 May 2010 (EST) Page template only. Content being prepared.
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 teh 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)
(Based on data from: Hassold, etal., Environ Mol Mutagen 1996. 28: 167-175)
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
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
References
Search
- NCBI Bookshelf oocyte | oogenesis | oocyte development
- Pubmed oocyte | oogenesis | oocyte development
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Cite this page: Hill, M.A. (2024, June 15) Embryology Oocyte Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Oocyte_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G