Oogensis
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This document discusses oogenesis, the process of egg formation in ovaries. It begins by defining oogenesis as the formation of eggs from the ovary. It then describes the key stages of oogenesis, including the development of primary oocytes from oogonia in the embryo, the resumption of meiosis at puberty, and the unequal cell divisions that result in a larger secondary oocyte retaining most of the cytoplasm. The document also compares oogenesis to spermatogenesis, noting the differences in gamete number, size, and timing of meiosis between the two processes.
Oogensis
- 1. oogenesis oogensis Name : Hafiz M Waseem Roll No : mcf-1901171 Class msc zoology(Evening) Submitted to: Dr. Sajda Naseem Submitted date: 15-1-2020
- 2. Contents Introduction Define oogenesis Maturation of mammalian oocyte Menstrual cycle Estrous cycle Dictyatestate Antrum Structure of ovum Comparison between oogenesis and spermatogenesis Difference between oogenesis and spermatogenesis
- 3. Introduction In human embryo oogonia divide rapidly from 2 to 7 month of gestation to form 7 million germ cells After 7 month of embryonic development no. of germ cell drops most oogonia die during this period and remaining oogonia enter the 1st meiotic division .Later cell called primery oocytes Onset of puberty group of oocytes periodically resume meiosis Define Formation of egg from ovary called oogenesis
- 4. Oogenesis When primary oocyte divides its nucleus called Germinal Vesicle At telophase one of 2 daughter cell contain hardly any cytoplasm. Other cell retain nearly entirely volume of cellular constituents. the smaller cell is called is called 1st polar body and larger cell called secondary oocytes. During second division of cytoplasm a similar unequal division of cytokinesis take place Most cytoplasm retained in mature egg
- 6. Maturation of mammalian oocytes 1st polar body does not divide Thus oogenic meiosis conserve volume of cytoplasm Maturation of mammalian oocytes 1. one type of ovulation is stimulated by act of copulation 2. Physical stimulation of cervix trigger the release of gonadotropin from pituitary signals the egg to resume meiosis and initiate event that will expel it from ovary
- 7. All oocytes remain in the *All oocytes remain in the dictyate state (quiescent) until stimulated by hormones during the menstrual cycle to continue their maturation
- 8. Menstrual cycle The maturing and releasing ova called menstrual cycle average about once every 29 days Menstrual cycle represents the integration of three very different cycle 1. The ovarian cycle :the function is to mature and release an oocytes 2. The uterine cycle : it provide appropriate environment for developing blastula stage. 3. The cervical cycle : it allow sperm to enter female reproductive track only at appropriate time
- 9. Release of mature egg
- 10. Estrus cycle In mammals the periodic ovulation patterns in which the female ovulates only at specific time of the year .this is called estrus In these animal environmental cues stimulates the hypothalamus to release GRH GRH stimulate pituitary to release the Gonadotropin FSH and LH it cause the ovarian follicles cells to proliferate and secrete estrogen Estrogen enter certain neuron and evokes pattern of mating behavior characteristic
- 11. Dictyate state The majority of oocytes in adult human ovary are maintained in deplotene stage of 1st meiotic prophase.it is called dictyate state each oocyte is enveloped by primordial follicle It consisting of epithelial granulosa cell Less organized layers of mesenchyme theca cell oocyte growth is an increase no. of granulose cell which form concentric layer around the oocyte this proliferation of granulosa cells is mediated by paracrine factors GDF9 a member of TGF-B family
- 12. Antrum In addition during the growth of follicle an antrum form and become filled with a complex of protein hormone and other molecules Maturing oocyte synthesized paracrine factor that allow follicle cell to proliferate the follicle cell secrete growth and differentiation factor TGF-B2 That allow the oocyte to grow and bring blood vessel into into follicular region The oocyte are maintained in dictayate state by ovarian follicle cells Release from dictayate state are reinitiating of meiosis are driven by LH hormone from pituitary
- 13. Release primary oocyte from dictyate state The pitutiaryis received by granolusa cell of ovary and it sad a paracrine signals that induce activation of mitosis promoting factors (MPF) in oocyte Transcribing gene present in growing oocyte , these gene products are necessary Cell metabolism Early development In mice growing diplotene oocyte is actively transcribing the gene for zona pellucida protein ZP1 ZP2 ZP3
- 14. These gene transcribe only in oocyte The fertilization mammalian oocytes is arrested in second meiotic metaphase by MPF
- 15. Many follicular cells and primery oocyte Follicul ar cell Primary oocyte 35 micro in diameter
- 16. Cuboidal cell form around developing primary oocyte Cuboidal cells
- 17. Multiply cell layer around developing primary oocyte Multiple layer of follicula r cell
- 18. Zona pellucida it is derive from follicular cells and primary oocyte Zona pellucida
- 20. Microvilli it is inject into fpllicular cell from prymary oocyte.it transfer nutrient er follicular cell
- 21. Entrum small space appear between follicular cell when follicular cell fuse to form small space appear between follicular cell
- 22. These cell fuse to form with each other to form entrum .it filled with fluid
- 23. Theca outermost layer of follicular cell called theca cell Theca layer Granulosa cell
- 24. Secondry oocyte formation primery oocyte divide to form secondry oocyte Primary oocyte divide by meiosis to form secondary oocyte
- 26. Fertilization of egg and sperm
- 27. Developmental stage of egg est rog en
- 28. Comparison of Oogenesis and Speratogenesis
- 29. Differences between spermatogenesis and oogenesis. 1. Four gametes from each primary spermatocyte 1. One gamete from each primary oocyte Spermatogenesis Oogenesis 2. Four small gametes of equal size 2. One large gamete + 2-3 polar bodies 3. Most cytoplasm is shed from spermatocyte 3. Cytoplasm conserved in one large gamete - may increase. Thus, in the final gamete there is a large amount of cytoplasm. 4. Diplotene relatively short 4. Dipotene very long - dictyate state 5. Functions in fertilization only after meiosis is complete 5. Often functions in fertilization before meiosis is complete
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