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53 Cards in this Set
- Front
- Back
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What is Oogenesis
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- cyclical process
- 12.5-51 years (38.5 yrs or 462 cycles) - every 28 days - ovarian and menstrual cycle - synchronized - controlled by hormones - positive and negative feedback |
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Ovarian cycle
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- cyclical development of oocyte and follicle and release of follicle
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Menstrual cycle
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- cyclical changes to endometrium and other parts of the tract
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# of primary oocytes at birth
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- 200,000 to 500,000 in each ovary
- do not produce new ones |
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Ovulation
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- release of mature (secondary) oocyte
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Atretic follicle
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- degenerating, unreleased follicle
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Prior to birth (oogenesis and follicular stages)
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- prior to birth
- oogonia (2n) divide by mitosis to produce primary oocytes (2n) - primary oocyte surrounded by primordial follicle (single layer, cuboidal) - enters meiosis I - arrested in prophase I at birth |
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Ovarian cycle and Menstrual cycle
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- synchronized
- monthly beginning at puberty - development of female gamete and changes to follicle |
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Changes that occur each month:
Primoridal follicle |
- stimulated to become primary follicles; single layer of cuboidal cells
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Changes that occur each month:
Primary follicle |
Stimulated to:
- add layers of cells to follicle wall - formation of fluid-filled hollow: Antrum - follicle cells begin secreting hormones (estrogen and testosterone) - results in secondary follicle |
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Changes that occur each month:
Secondary follicle |
- results from growth of primary follicle over several months
- many become atretic - few develop into tertiary follicles |
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Changes that occur each month:
Tertiary follicle |
- develops into Graafian follicle
- granulosa cells develop connections to oocyte and each via gap junctions |
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Graafian follicle/Mature follicle
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- antrum containing hormones, anti-coagulants, elements of plasma from thecal vessels
- granulosa cells; secrete estrogen - theca folliculi (outer fibrous capsule, inner vascular/secretory produces testosterone) - zona pellucida - corona radiata - cumulus oophorous - oocyte re-enters meiosis and develops from primary to secondary oocyte |
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Primary oocyte changes
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- completes meiosis I (unequal division)
- produces secondary oocyte (n) and first polar body (n); usually degenerates |
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Secondary oocyte changes
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- enters meiosis II
- arrested in metaphase II - ovulated in metaphase II - usually one oocyte/follicle completes maturation process each month |
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Fate of secondary oocyte
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- no fertilization = degeneration
- fertilization = completion of meiosis II (unequal division) produces ovum (n) and second polar body (degenerates) - when fertilization is complete; product is zygote |
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Ovarian cycle phases (3)
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- follicular phase (day 1-10)
- ovulatory phase (day 10-15) - luteal phase (day 15-28) |
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Menstrual cycle phases (3)
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- menstrual phase (day 1-5)
- proliferative phase (day 5-14) - secretory phase (day 14-28) |
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Day 1 of 28 day cycle
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- first day of menstruation
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4 integrated processes in synchrony
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- neuroendocrine events
- oogenesis/follicular events - ovarian endocrine events - uterine events |
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Day #1 events
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- GnRH diurnal cycles/pulses; secreted from hypothalamus; low level; stimulates secretion of LH and FSH (low level) from pituitary
- LH and esp. FSH stimulate start of follicle growth and oocyte maturation - ovarian hormones (progesterone and estrogen) are very low - menstruation: shedding of endometrium (stratum functionalis) |
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Day #1-10 events of follicular phase
Pituitary |
- GnRH secreted at modest rate
- slight increase in LH and FSH (day 3) - secretion of LF and FSH level out - FSH and LH stimulate development of tertiary ovarian follicles - does not initiate ovulation |
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Day #1-10 events of follicular phase
Follicle |
- follicle enlarges to early Graafian follicle
- granulosa cells divide: several cell layers - follicle cells develop numerous gap junctions - follicle cells secrete glycoproteins from acellular zona pellucida - initial development of follicle can proceed without pituitary hormones - development of mature Graafian follicle depends on FSH and LH |
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Day #1-10 events of follicular phase
Oocyte |
- oocyte grows
- material from blood vessels in medulla and theca externa (no blood vessels within follicle itsel) - dominant follicles secrete suppressors to prevent development of additional follicles |
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Day #1-10 events of follicular phase
Hormones |
- more gonadotropins (LH, FSH) cause follicle to secrete more estrogen (estradiol 17 β) and androgens (testosterone)
- LH -> theca interna = androgens; andostenedione (converted to estrogen) - FSH -> granulosa cells = estrogen; from androgens and cholesterol |
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Day #10-14 events of ovulatory phase
Day 10-11 |
- LH increases due to more estrogen (positive feedback)
- FSH remains low, falls slightly due to production of inhibin in granulosa cells and differential effects of GnRH on cells that produce LH and FSH |
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Day #10-14 events of ovulatory phase
Day 12-13 |
- rapid rise in FSH
- due to side effect of increase in GnRH associated with increase in LH |
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Increase in LH associated with
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- stimulates development of Graafian follicle
- follicle fills with fluid bulges at ovary surface - initiates production of progesterone - stimulates resumption of meiosis in primary oocytes |
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Cyclins
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- proteins involved in regulation of cell cycle
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Kinases
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- enzymes involved in cell cycle
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cdc genes
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- genes encoding for proteins involved in cell cycle
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Cyclins regulate
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- activity of cdc2 and other cyclin dependent kinases (CDK)
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MPF
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- maturation promoting factor or m-phase promoting factor
- cdc2 + cyclin regulators |
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Meiotic arrest in Prophase I
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- c-AMP transferred from granulosa cells to oocyte via gap junctions (primordial follicle)
- production of MIP (meiosis inhibitory protein) prevents meiotic activity - LH interrupts transfer of c-AMP to oocyte by reducing gap junctions - increased progesterone (due to LH) activates MPF - MPF composed of kinase "a" (enzyme) and cyclin B (protein) - progesterone stimulates production of c-Mos (protein) - c-Mos activates cyclin B - cyclin B activates kinase "a" (requires gene cdc2) - kinase "a" stimulates breakdown of nuclear membrane (germinal vesicle) of primary oocyte (phosphorylation of lamins in membrane) - kinase "a" also stimulates condensation of chromosomes - activated primary oocyte progresses to metaphase I |
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Activated primary oocyte in Metaphase I
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- cyclin is degraded, cell division is completed
- cyclin prevents cell from entering anaphase - end of division (meiosis I) - MPF levels are low - new cyclin B is generated - initiates meiosis II - result of meiosis I = secondary oocyte in mature Graafian follicle and first polar body (degenerates) |
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Secondary oocyte in Meiosis II
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- continues meiosis II until arrested in Metaphase II
- arrest due to presence of csf (cytostatic factor) - csf consists of cMos and kinase "b" (CDK2) - csf prevents cyclin from degrading - degradation of cyclin required for anaphase II - in humans; trigger for breakdown of cyclin is fertilization - fertilization required to complete meiosis |
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Day #10-14 events of ovulatory phase
Day 13-14 |
- secretion of estrogen continues to increase then falls
- progesterone begins to be secreted by granulosa cells - progesterone secretion is response to increasing LH |
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Ovulation
Day 14-15 |
- ovulation 12-36 hours after LH surge
- usually one or two follicles mature - most sensitive to LH surge, suppresses other follicles - ovulatation occurs - LH and FSH peak rapidly then drop |
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Graafian follicle response to LH surge
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- follicle bursts due to physical pressure against ovary surface
- stretching and thinning of ovary surface (stigma) - secretion of plasmin and collagenase, prostaglandins and histamines |
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Secondary oocyte released
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- in metaphase II
- covered in follicle cells (corona radiata, part of cumulus oophorus) - released into peritoneal cavity - captured by fimbriae - remaining granulosa cells collapse - antrall/follicular fluid released - small clot forms in collapsed follicle (corpus hemorrhagicum) - estrogen and progesterone show little change - uterus completes proliferative phase, enters secretory phase |
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Day #15-28 of luteal phase
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- varies in length, 12-14 days
- e.g. 25 day cycle (7+4+14=25) 35 day cycle (17+4+14=35) |
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Day #15-28 of luteal phase
Events |
- collapsed follicle transforms to corpus luteum
- granulosa cells hypertrophy and accumulate lipid (and carotene) = lutein cells - corpus luteum = temp endocrine gland, requires LH - secretes progesterone and estradiol 17 β |
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Corpus luteum if no fertilization
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- degenerates starting at day 23
- progesterone drops - high levels of both progesterone & estrogen (before day 23) - negative feedback on hypothalamus & pituitary - reduces LH and FSH - inhibin from ovary (granulosa cells) inhibits FSH - inhibin produced when estrogen is high - decrease in LH and FSH (along with inhibin) inhibits new follicles and prevents ovulation - develops into corpus albicans, sinks inwards and disappears |
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Drop in LH level causes
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- corpus luteum cells begin to die
- progesterone and estrogen levels drop - increase in secretion of GnRH, LH and FSH (day 26-28) |
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If fertilization occurs
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- corpus luteum becomes corpus luteum of pregnancy
- continues secreting until placenta takes over |
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Uterus in Secretory phase
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- changes b/c of progesterone
- thickening of stratum functionalis (6.0 mm), edema of tissue, secretion in uterine glands (glycogen) - coiled arteries elongate, become more convoluted - progesterone falls (day 26-28), results in premenstrual changes in spiral arteries (constriction, necrosis, dilation) - endometrium shrinks to 3-4mm - necrosis prepares endometrium for menstruation |
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Other changes during ovarian/menstrual cycle:
Fallopian tube |
follicular phase
- cilia increase in distal parts of tube (b/c of increase in estrogen) - rate of secretion also increases (also b/c of estrogen) preovulatory and immediately postovulatory - ciliation, rate of ciliary beat (response to progesterone) and secretion, reach maximum around time of ovulation - blood engorgement of fimbriae greatest luteal phase - progesterone increases cause cilia decrease - ciliary beat declines - secretory activity decreases |
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Other changes during ovarian/menstrual cycle:
Vagina |
- little change in vagina in humans
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Other changes during ovarian/menstrual cycle:
Uterine Cervix |
- cervical mucus membrance NOT shed
- mucus glands secrete constantly (60mg/day) - undergoes cyclical changes each month follicular phase - cervical muscles contracted - mucus: low level of secretion, viscous, hostile to sperm near ovulation (due to increased estrogen) - cervical muscles relax, opening os slightly - mucus becomes thinner - mucus volume increases up to 10x - changes in electrolyte and pH - more sperm friendly Luteal phase (increased progesterone) - cervical muscles contracted - less mucus, thick and hostile If pregnant - mucus forms a plug |
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Day 1-5 of Menstrual Phase
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- low ovarian hormones (esp progesterone)
- stratum functionalis is shed - menstrual flow lasts 3-7 days (average 4-5) - coiled arteries constricted for 2 days, then dilate into damage tissue - tissue necrosis results from lysozymal enzymes and lack of blood - small vessels break; blood and damaged tissue released into lumen of uterus |
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Menstrual flow contents
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1. arterial and venous blood (plasmin dissolves clots, keeps blood liquid)
2. epithelial cells from stratum functionalis 3. mucus and other secretory materials from uterine and cervical glands - averages 30-80 ml to 250 ml - volume increases with IUD, decreases with the pill - tends to decrease with age |
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Around day 4 of Menstrual phase
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- repair of stratum functionalis
- mitosis of epithelial (generative) cells in stratum basalis - regeneration of blood vessels (esp spiral arteries) - end of menstrual phase endometrium is 0.5-3.0 mm, consists mostly of stratum basale |
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Day 5-14 of Proliferative phase
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- thickening of stratum functionalis
- tubular (uterine/endometrial) glands enlarge - spiral arteries proliferate and elongate - caused by rising level of estrogen - secreted by ovarian follicle in response to FSH |
