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Reproductive System > Oogenesis > Flashcards

Oogenesis Flashcards

1
Q

structure of ovaries

A
  • 2-3cm long
  • attached to broad ligament
    helpful: circles at ends of fallopian tubes
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2
Q

fallopian tubes and egg

A
  • egg released from one ovary into abdominal cavity during ovulation
  • fimbriae (finger-like projections) at end of fallopian tube
  • fimbriae sensitive to hormonal cues - when egg released the fimbriae closest to ovary become mobile and actively sweep across surface of ovary to guide egg into entrance of fallopian tube
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3
Q

egg travel after release from ovary

A

ovary -> FT: fimbriae (part of IF) into infundibulum -> FT: ampulla -> FT: isthmus -> intramural portion -> uterus

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4
Q

describe ampulla structure

A
  • widest part of fallopian tube
  • longest part of fallopian tube
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5
Q

describe isthmus structure

A
  • narrower portion of fallopian tube
  • portion closer to uterus
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6
Q

what is the infundibulum in female reproductive tract

A

funnel-shaped entrance into fallopian tubes

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7
Q

where does fertilisation occur?

A

in ampulla or isthmus

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8
Q

where does implantation of embryo (fertilised egg) occur

A

in uterine epithelium (uterine wall)

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9
Q

what is intramural (interstitial) portion [not always needed]

A
  • fallopian tube that extends into top of uterus
  • opens into uterine cavity
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10
Q

what is the centre of the ovary called?

A

ovarian medulla

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11
Q

where do we see follicles in ovary?

A

in ovarian medulla scattered at varying points of progression

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12
Q

list the progression of follicles

A

primordial follicle -> primary follicle (preantral) -> secondary follicle -> tertiary follicle (pre-ovulatory follicle - may ovulate)

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13
Q

fate of more than 99% of follicles

A

become atretic

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14
Q

only 1% of follicles….

A

ovulate

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15
Q

after ovulation occurs what occurs to follicle

A

change in structure
to form corpus luteum

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16
Q

function of corpus luteum

A

produce progesterone
to signal that implantation may occur in body

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17
Q

what happens to oogonia before birth

A

enter meiosis and become primary oocytes

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18
Q

when do primary oocytes become suspended

A

during prophase 1 during diplotene phase
around time of birth

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19
Q

how many primary oocytes around time of birth

A

300,000

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20
Q

how many primary oocytes will end up ovulated

A

3-400

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21
Q

what happens to the rest of the primary oocytes that are not ovulated and when

A

lost to atresia until time of menopause (~early 50s)

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22
Q

before puberty what happens to primordial follicles and primary oocytes

A

every day a few primordial follicles differentiate to primary follicles
primary oocytes remain at diplotene

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23
Q

is differentiation into primary follicles gonadotrophin dependent, if not what is it?

A

no (hence happens before puberty)
controlled by intraovarian factors

24
Q

what happens to all developing follicles prior to puberty

A

become atretic (degenerate)

25
Q

structure of a primordial follicle

A

small oocyte
surrounded by squamous granulosa cells
surrounded by basement membrane - separates follicle from stroma

26
Q

structure of primary follicle

A

oocyte grows & secretes zona pellucida (+ more organelles incl mitochondria being produced)
increase amount granulosa cells and become cuboidal
formation of thecal layer from stroma cells
basement membrane separating from thecal later

27
Q

what is zona pellucida

A

surrounds oocyte
layer primarily composed of glycoproteins
formation at primary follicle stage

28
Q

what hormones do we see the production of after puberty

A
  • steroid hormones - progesterone, oestrogen
  • increases in FSH and LH
29
Q

WHAT is regulated by hormonal changes across the menstrual cycle

A

ovulation

30
Q

what is further development of primary follicles dependent on

A

hormonal changes across menstrual cycle after puberty

31
Q

what hormone and feedback prevents ovulation

A

negative feedback by progesterone (high levels of progesterone)

32
Q

what happens after some time to progesterone if implantation hasn’t occurred (progesterone is high following ovulation)

A

progesterone declines from influence of prostaglandins produced by uterus, then menstrual cycle begins again

(implantation occurs after ovulation)

33
Q

when do we see an increase in production of secondary follicles

A

from puberty

34
Q

structure of secondary (antral) follicles

A
  • increase in thecal and granulosa cells
  • theca organised into vascularised theca interna & outer fibrous theca externa
  • accumulation of fluid between granulosa cells
  • slight increase oocyte size
  • development of follicular antrum that surrounds oocyte(follicle fluid-filled cavity)
  • oocyte still attached to granulosa cells through specialised subpopulation of granulosa cells called cumulous oophorus which suspended from mural granulosa of follicle wall
35
Q

cumulous cells function

A

attached to oocyte at time of ovulation
important for subsequent maturation of oocyte

36
Q

what does production of oestradiol by secondary follicle rely on

A

uptake of cholesterol from thecal layer

37
Q

what do secondary follciles produce

A
  • ovarian steroids - oestradiol, progesterone
38
Q

explain how thecal layer takes up cholesterol and makes androgens

A
  • theca interna highly vascular
  • cells of theca interna take up cholesterol from blood and synthesise androgens (testosterone, DHT)
  • androgens cross basement membrane to granulosa cells that convert androgens to oestradiol
39
Q

what dictates more oestradiol production

A

size of secondary follicle, in particular the follicle destined to ovulate

40
Q

is ovulation initiated by positive or negative feedback

A

positive feedback

41
Q

outline positive feedback in ovulation (3 steps)

A
  1. decline in progesterone & increase in oestradiol late in luteal phase - triggers ovulation
  2. creates positive feedback on hypothalamus causing increased LH and FSH secretion by anterior pituitary
  3. LH surge causes preovulatory follicle to rupture -> resulting egg gets ovulated
42
Q

explain how LH causes ovulation

A
  • LH surge acts via LH receptors on granulosa cells
  • follicle rupture induced by proteases (inside follicle)
  • follicle collapses
    -> granulosa cells lutenised (change function)
    -> corpus luteum formed (& produces progesterone)
43
Q

what happens at the same time as LH surge in oocyte

A

resumption of meiosis

44
Q

what happens in resumption of meiosis for oocyte

A

meiosis I completed -> forming secondary oocyte (suspended) & extrusion of first polar body

45
Q

what does the first polar body contain?

A

chromosomes that are redundant during meiosis

46
Q

when is meiosis II completed? / resumption of meiosis II on suspended secondary oocyte

A

at time of fertilisation - when sperm penetrates membranes surrounding oocyte

47
Q

when is cAMP relevant and at what levels

A

decreased cAMP during resumption and completion of meiosis I (prior to ovulation)

48
Q

at menopause are there many follicles left

A

no, nearly all gone

49
Q

what is steroid hormone production by ovary like during menopause

A

little / no steroid hormone production => negative feedback is removed causing increased FSH levels which are a menopause indicator

50
Q

at what age do we see a decline in female fertility

A

~35 years old

51
Q

what causes decline in female fertility

A

decrease in oocyte quality (developmental competence)

52
Q

what characterises decreased oocyte quality

A

increased incidence of aneuploidy (incorrect chromosome number) = increased rate of miscarriage in women aged 35 and over even though pregnancy can occur

53
Q

at what age does male fertility decline

A

~40years old but not as dramatically

54
Q

what testing allows embryos to be screened for aneuploidy => improve success rates of IVF

A

preimplantation genetic testing (PGT-A)

55
Q

compare success rates of women aged 35 vs under 35

A

> 35 yrs - less than 10% - still relatively low
<35 yrs - over 30%

56
Q

describe PGT-A

A

take usually 5 cells from blastocyst embryo stage
taken to lab to determine chromosome number, particularly whether aneuploid embyro
blastocysts frozen then transferred at a subsequent cycle once results known

57
Q

why is there an increase in freezing of oocytes below age 35

A

to preserve fertility
~10% women use these oocytes, get pregnant nonetheless without accessing these

Reproductive System (21 decks)

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