1.2 - Origin of the gametes - females Flashcards
what does gamete production involve?
proliferation of germ cells by mitosis
what happens after proliferation of germ cells by mitosis?
genetic reshuffling & reduction to haploid meiosis
what has to happen to form mature gamete?
cyto-differentiation (development of specialised structures and functions in embryonic cells)
where do the female primordial germ cells colonise?
in the cortex of the primordial gonad becoming oogonia
how do oogonia proliferate?
rapidly by mitosis
7million by 20 weeks
what happens to the 7 million oogonia in the cortex of primordial gonad?
most die during gestation, leaving about 2 million
what happens to the 2 million oogonia which survive gestation in the cortex of primordial gonad?
begin meiosis before birth
becoming primary oocytes (egg cells)
what is entry into meiosis 1 stimulated by?
mesonephric cells
what are mesonephric cells?
flattened epithelial cells called follicle cells
what do follicle cells surround? forming?
the primary oocytes to form primordial follicles
when does meiosis arrest?
at the diplotene stage (resting stage) of prophase
why does meiosis arrest at the diplotene stage of prophase?
due to oocyte maturation inhibitor (OMI) from follicular cells
what is the primordial follicle?
primary oocyte surrounded by the follicular cells
when does a woman have all the oocytes she will ever have?
at birth
where are all ova produced from?
the ‘stock’ of oocytes the woman has at birth - no more can be formed later (in terms of oocytes)
what does meiosis arresting at diplotene stage of prophase increase the chance of?
cell damage
increasing risk of fetal chromosomal abnormalities in pregnancies of older women
what happens at puberty until menopause about 40 years later?
a small number of follicles begin further development each day (not oocyte - what the follicles surround)
what are the stages a follicle requires to go through before forming a mature gamete?
- pre-antral / primordial follicle
- antral follicle (Graafian / vesicular follicle)
- pre-ovulatory follicle
what happens to the primary oocyte in primordial to pre-antral (1st stage)?
the primary oocyte grows dramatically, but doesn’t re-start meiosis
what happens to the follicular cells in primordial to pre-antral (1st stage)?
change from flat to cuboidal cells
what happens to the cuboidal cells (from flat) in primordial to pre-antral (1st stage)? called?
proliferate to form multiple layered epithelium - granulosa cells
what is the granulosa cells’ function?
to secrete glycoprotein to surround the primary oocyte with a zona pellucida
what do surrounding stromal (connective tissue) cells form?
a theca folliculi with 2 parts
what are the 2 parts of the theca folliculi?
inner: theca interna (vascular and endocrine)
outer: theca externa (fibrous & capsule)
what secretes oestrogen?
theca and granulosa cells collaborate to secrete oestrogens
what happens to the granulosa cells in antral transition?
continue to proliferate, fluid appears between them, eventually forming an antrum
what happens as more fluid forms between the granulosa cells in antral transition?
secondary / Graafian follicle (2nd (antral) stage) expands dramatically
in humans, antral follicles expand to what size? under what stimulation?
2mm diameter
withOUT stimulation by reproductive hormones
what does continued development of Graafian follicle depend upon?
follicle stimulating hormone (FSH)
how does FSH function?
binds ONLY to granulosa cells of lutinising hormong (LH)
which binds ONLY to thecal cells (formed from surrounding stroma)
in each cycle, what happens to the follicles?
usually, only 1 follicle becomes dominant and develops further
how does the dominant follicle develop? (under what stimulation)
- under the influence of LH, thecal cells secrete androgens
- androgens converted to oestrogens by granulosa cells under influence of FSH
(FSH –(bind)–> granulosa cells of LH –(bind)–> thecal cells –(secrete)–> androgens–(converted)–> oestrogen)
when does the pre-ovulatory follicle phase begin? stimulated by?
37 hours before ovulation
under the influence of oestrogen
where do receptors for LH appear?
on the outer granulosa cells
what is the pre-ovulatory follicle –> ovulation stimulated by?
an LH surge
leading to rapid changes in the follicle
what happens within 3 hours of LH surge?
oocyte re-starts meiosis - 1st meiotic division is completed
how can one describe the division of the completed first meiotic division?
asymmetric: cytoplasm remains with 1 daughter
the other forms a condensed polar body
what happens to the secondary follicle? (in pre-ovulatory follicle stage - 3rd)
enters meiosis II and then arrests again 3 hours prior to ovulation
when does follicle size increases dramatically? what happens to the structure?
by increase in antral fluid volume (full size being 25mm) and the structure begins to weaken
what does LH stimulate in pre-ovulatory stage?
stimulates collagenase activity, leading to follicle rupture
what happens to the ovum in pre-ovulatory stage after LH has stimulated collagenase leading to follicle rupture??
the ovum (egg) is carried out in the fluid and gathered up into the fallopian tube by fimbria
when is meiosis completed?
when the ovum is fertilised
what happens to unfertilised cells?
degenerate 24 hours after ovulation
what happens to the remains of the follicle after ovulation?
re-organise themselves into a corpus luteum
what does corpus luteum secrete? influenced by what?
progesterone and oestrogen
under influence of LH
how long does corpus luteum live for before regressing?
14 days before regressing spontaneously (in absence of a fertilised ovum)
what are the early antral to corpus luteum stages synchronised with?
the reproductive cycle of female
what happens in the menstrual cycle of humans?
the lining of the uterus is shed between cycles as a menstrual bleed
when does rapid antral development begin?
towards the end of menstruation, culminating in ovulation about 10 days later (12-14 days after onset of menstrual bleed)
what happens to the corpus luteum in the absence of pregnancy?
present for 14 days before it regresses and a new menstrual bleed begins
what is the ovarian cycle?
the pattern of ovarian changes during the menstrual cycle
