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BIOC19H3 Chapter Notes -Oogenesis, Germ Cell, Meiosis

Biological Sciences
Course Code
Ian Brown

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Time span differences
Four haploid sperm cells – each able to potentially fertilize an egg
Produced by meiosis from each diploid stem cell triggered into sperm cell differentiation
One large haploid egg (receiving bulk of cytoplasm) and 3 small haploid polar bodies
Produced by meiosis from each diploid stem cell triggered into oogenesis

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Interrelated Ovary Functions
1. Oogenesis – production of haploid female gametes
2. Production of steroid hormone – estrogen and progesterone
Steroid hormones – estrogen and progesterone
Estrogen – promotes growth and maturation of internal and external sex organs
Responsible for female characteristics that develop at puberty
Progesterone – prepares uterus for pregnancy
Maintains pregnancy – decrease mother’s immune response to enable gestation,
decreases contractibility of uterus muscle, inhibits lactation
Drop in progesterone during pregnancy may be involved in inducing labor
Oogenesis begins during fetal development
In ovary, mitotic division massively increase number of oogonia (egg germ cells)
Meiosis initiated – 11-12 weeks of gestation in humans
Prophase I meiosis – homologous chromosomes undergo pairing and exchange genetic
material via recombination, cells referred to as primary oocytes
Primordial follicles – primary oocytes surrounded by somatic pre-granulosa cells
Primordial follicles are quiescent for yeast until puberty, then recruited monthly to
undergo growth process
Ovarian follicle provides ‘microenvironment’ for developing oocyte

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Folliculogenesis – Growing follicles
1. Primary follicle
Initial recruitment – primordial follicles induced to develop, thought to involve growth
Increases in size
Granulosa cells – oocyte englarges, follicular cells multiply
Increase number of free ribosomes, mitochondria, RER
Zona pellucida formed – enable specie-specific binding of sperm
Follicle cells thicken
Follicle cells have receptors for FSH – but development remains gonadotropin-
2. Secondary follicle
Gap junctions develop between granulosa cells
Basal layer of granulosa cell do NOT form tight junctions – no blood-follicular barrier
Granulosa layer uniform in size except where oocyte is – thickened mound called
cumulus oophorus
Antrum formed – follicular growth now dependent on FH and LH
Increase in LH receptors on granulose cell
Theca folliculi – oocyte secretes factors that recruit CT cells resulting in sheath
surrounding granulose cells
Theca interna – highly vascularized, cell have LH receptor
LH stimulates them to make and secrete androgens (precursors to
Theca externa – muscle and CT
Early Late
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