1.2 - Origin of the gametes - females

Question 1

what does gamete production involve?

Answer 1

proliferation of germ cells by mitosis

Question 2

what happens after proliferation of germ cells by mitosis?

Answer 2

genetic reshuffling & reduction to haploid meiosis

Question 3

what has to happen to form mature gamete?

Answer 3

cyto-differentiation (development of specialised structures and functions in embryonic cells)

Question 4

where do the female primordial germ cells colonise?

Answer 4

in the cortex of the primordial gonad becoming oogonia

Question 5

how do oogonia proliferate?

Answer 5

rapidly by mitosis

7million by 20 weeks

Question 6

what happens to the 7 million oogonia in the cortex of primordial gonad?

Answer 6

most die during gestation, leaving about 2 million

Question 7

what happens to the 2 million oogonia which survive gestation in the cortex of primordial gonad?

Answer 7

begin meiosis before birth

becoming primary oocytes (egg cells)

Question 8

what is entry into meiosis 1 stimulated by?

Answer 8

mesonephric cells

Question 9

what are mesonephric cells?

Answer 9

flattened epithelial cells called follicle cells

Question 10

what do follicle cells surround? forming?

Answer 10

the primary oocytes to form primordial follicles

Question 11

when does meiosis arrest?

Answer 11

at the diplotene stage (resting stage) of prophase

Question 12

why does meiosis arrest at the diplotene stage of prophase?

Answer 12

due to oocyte maturation inhibitor (OMI) from follicular cells

Question 13

what is the primordial follicle?

Answer 13

primary oocyte surrounded by the follicular cells

Question 14

when does a woman have all the oocytes she will ever have?

Answer 14

at birth

Question 15

where are all ova produced from?

Answer 15

the ‘stock’ of oocytes the woman has at birth - no more can be formed later (in terms of oocytes)

Question 16

what does meiosis arresting at diplotene stage of prophase increase the chance of?

Answer 16

cell damage

increasing risk of fetal chromosomal abnormalities in pregnancies of older women

Question 17

what happens at puberty until menopause about 40 years later?

Answer 17

a small number of follicles begin further development each day (not oocyte - what the follicles surround)

Question 18

what are the stages a follicle requires to go through before forming a mature gamete?

Answer 18

1. pre-antral / primordial follicle
2. antral follicle (Graafian / vesicular follicle)
3. pre-ovulatory follicle

Question 19

what happens to the primary oocyte in primordial to pre-antral (1st stage)?

Answer 19

the primary oocyte grows dramatically, but doesn’t re-start meiosis

Question 20

what happens to the follicular cells in primordial to pre-antral (1st stage)?

Answer 20

change from flat to cuboidal cells

Question 21

what happens to the cuboidal cells (from flat) in primordial to pre-antral (1st stage)? called?

Answer 21

proliferate to form multiple layered epithelium - granulosa cells

Question 22

what is the granulosa cells’ function?

Answer 22

to secrete glycoprotein to surround the primary oocyte with a zona pellucida

Question 23

what do surrounding stromal (connective tissue) cells form?

Answer 23

a theca folliculi with 2 parts

Question 24

what are the 2 parts of the theca folliculi?

Answer 24

inner: theca interna (vascular and endocrine)
outer: theca externa (fibrous & capsule)

Question 25

what secretes oestrogen?

Answer 25

theca and granulosa cells collaborate to secrete oestrogens

Question 26

what happens to the granulosa cells in antral transition?

Answer 26

continue to proliferate, fluid appears between them, eventually forming an antrum

Question 27

what happens as more fluid forms between the granulosa cells in antral transition?

Answer 27

secondary / Graafian follicle (2nd (antral) stage) expands dramatically

Question 28

in humans, antral follicles expand to what size? under what stimulation?

Answer 28

2mm diameter | withOUT stimulation by reproductive hormones

Question 29

what does continued development of Graafian follicle depend upon?

Answer 29

follicle stimulating hormone (FSH)

Question 30

how does FSH function?

Answer 30

binds ONLY to granulosa cells of lutinising hormong (LH) | which binds ONLY to thecal cells (formed from surrounding stroma)

Question 31

in each cycle, what happens to the follicles?

Answer 31

usually, only 1 follicle becomes dominant and develops further

Question 32

how does the dominant follicle develop? (under what stimulation)

Answer 32

1. under the influence of LH, thecal cells secrete androgens 2. androgens converted to oestrogens by granulosa cells under influence of FSH (FSH --(bind)--> granulosa cells of LH --(bind)--> thecal cells --(secrete)--> androgens--(converted)--> oestrogen)

Question 33

when does the pre-ovulatory follicle phase begin? stimulated by?

Answer 33

37 hours before ovulation | under the influence of oestrogen

Question 34

where do receptors for LH appear?

Answer 34

on the outer granulosa cells

Question 35

what is the pre-ovulatory follicle --> ovulation stimulated by?

Answer 35

an LH surge | leading to rapid changes in the follicle

Question 36

what happens within 3 hours of LH surge?

Answer 36

oocyte re-starts meiosis - 1st meiotic division is completed

Question 37

how can one describe the division of the completed first meiotic division?

Answer 37

asymmetric: cytoplasm remains with 1 daughter | the other forms a condensed polar body

Question 38

what happens to the secondary follicle? (in pre-ovulatory follicle stage - 3rd)

Answer 38

enters meiosis II and then arrests again 3 hours prior to ovulation

Question 39

when does follicle size increases dramatically? what happens to the structure?

Answer 39

by increase in antral fluid volume (full size being 25mm) and the structure begins to weaken

Question 40

what does LH stimulate in pre-ovulatory stage?

Answer 40

stimulates collagenase activity, leading to follicle rupture

Question 41

what happens to the ovum in pre-ovulatory stage after LH has stimulated collagenase leading to follicle rupture??

Answer 41

the ovum (egg) is carried out in the fluid and gathered up into the fallopian tube by fimbria

Question 42

when is meiosis completed?

Answer 42

when the ovum is fertilised

Question 43

what happens to unfertilised cells?

Answer 43

degenerate 24 hours after ovulation

Question 44

what happens to the remains of the follicle after ovulation?

Answer 44

re-organise themselves into a corpus luteum

Question 45

what does corpus luteum secrete? influenced by what?

Answer 45

progesterone and oestrogen | under influence of LH

Question 46

how long does corpus luteum live for before regressing?

Answer 46

14 days before regressing spontaneously (in absence of a fertilised ovum)

Question 47

what are the early antral to corpus luteum stages synchronised with?

Answer 47

the reproductive cycle of female

Question 48

what happens in the menstrual cycle of humans?

Answer 48

the lining of the uterus is shed between cycles as a menstrual bleed

Question 49

when does rapid antral development begin?

Answer 49

towards the end of menstruation, culminating in ovulation about 10 days later (12-14 days after onset of menstrual bleed)

Question 50

what happens to the corpus luteum in the absence of pregnancy?

Answer 50

present for 14 days before it regresses and a new menstrual bleed begins

Question 51

what is the ovarian cycle?

Answer 51

the pattern of ovarian changes during the menstrual cycle