Folliculogenesis and ovulation

Question 1

Label this ovary

Answer 1

Question 2

Describe the anatomy and function of the follicle

Answer 2

Contains and matures oocyte (egg)
Fluid filled
Secreted oestradiol (induces oestrus)

Question 3

Describe the anatomy and function of the CL

Answer 3

highly vascularised, transient endocrine gland
solid
progesterone production

Question 4

Describe early germ cell development (formation of primary oocytes)

Answer 4

Primordial germ cells migrate from yolk sac => hind gut => developing gonad
Proliferate by mitosis to become oogonia
Oogonia develop in interconnected clusters/’egg nests’
Oogonia enter meiosis to become primary oocytes

Question 5

Describe the development of primordial follicles

Answer 5

Eggs nest break apart
oocytes associates with somatic granulosa cells => primordial follicles
Entire population undergo meiotic arrest (prophase I) until puberty to protect DNA

Question 6

What are the phases of antral follicle growth

Answer 6

Recruitment - small follicles
Selection - medium follicles
Dominance - large follicles

Question 7

Describe antral follicle recruitment

Answer 7

Small antral follicles start to develop initiated by FSH wave
Secrete small amount of oestradiol
some undergo atresia (death)

Question 8

Describe antral follicle selection

Answer 8

Cohort of growing follicle dependent on FSH for support
Produce inhibin and oestradiol (-ve feedback on pituitary -> suppresses FSH)
Become dependent on LH
some undergo atresia

Question 9

Describe antral follicle dominance

Answer 9

Transition from FSH to LH dependence (LH receptors appear in granulosa cells)
Increased oestradiol and inhibin production (inhibits growth of other follicles)
Ovulate or undergo atresia depending on fall in progesterone levels

Question 10

What stage of antral follicle development is this?

Answer 10

Recruitment

Question 11

what stage of antral follicle development is this?

Answer 11

Selection

Question 12

What stage in antral follicle growth is this?

Answer 12

dominance

Question 13

Describe the follicular production of estradiol

Answer 13

Stimulated by FSH and LH
Co-ordinated action of theca and granulosa layers
Theca cells reacts to LH - cholesterol => testosterone
Granulosa cells reacts to FSH - testosterone => oestradiol (aromatase = enzyme)

Question 14

What causes ovulation/release of the oocyte?

Answer 14

oestradiol => LH surge => ovulation

Question 15

Describe the hormonal changes from luteolysis to ovulation

Answer 15

Luteolysis => Decreased progesterone
Increased GnRH
Increased FSH and LH
follicular development
Increased inhibin => decreased FSH
Increased oestradiol to threshold => preovulatory LH surge => ovulation

Question 16

Describe the role of PGE2 and PGF2a in ovulation

Answer 16

Preovulatory LH surge causes increase in PGE2 and PGF2a
PGE2 => increased blood flow to ovary and dominant follicle => oedema => increased follicular pressure => ovulation
PGF2a => release of lysosomal enzyme which weakens follicular wall and increased contraction of ovarian smooth muscle which increases follicular pressure => ovulation

Question 17

How does the shift from oestradiol to progesterone by the dominant follicle (due to the LH surge) lead to ovulation?

Answer 17

Increased progesterone => increased collagenase (dissolves collagen which occludes over tunica albuminica and basement membrane) => weakens follicular wall => ovulation

Question 18

Describe the process of releasing the oocyte from a follicle

Answer 18

Follicular wall bursts releasing oocyte and granulosa cells from granulosa cell anchor point
oocyte carried with follicular fluid into peritoneal cavity where it is captured by fimbria on the infundibulum

Question 19

Describe the process of oocyte maturation after the LH surge causing ovulation

Answer 19

Nuclear maturation:
- completion of meiosis I, arrested again in meiosis II
Fertilisation:
- critical rise in Ca2+
- induces completion of meiosis II
- 2nd polar body formed

Question 20

What causes ovulation to be induced in queens?

Answer 20

Nerves endings in vagina and cervix are stimulated at copulation => LH surge