Folliculogenesis and ovulation Flashcards
Label this ovary
Describe the anatomy and function of the follicle
Contains and matures oocyte (egg)
Fluid filled
Secreted oestradiol (induces oestrus)
Describe the anatomy and function of the CL
highly vascularised, transient endocrine gland
solid
progesterone production
Describe early germ cell development (formation of primary oocytes)
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
Describe the development of primordial follicles
Eggs nest break apart
oocytes associates with somatic granulosa cells => primordial follicles
Entire population undergo meiotic arrest (prophase I) until puberty to protect DNA
What are the phases of antral follicle growth
Recruitment - small follicles
Selection - medium follicles
Dominance - large follicles
Describe antral follicle recruitment
Small antral follicles start to develop initiated by FSH wave
Secrete small amount of oestradiol
some undergo atresia (death)
Describe antral follicle selection
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
Describe antral follicle dominance
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
What stage of antral follicle development is this?
Recruitment
what stage of antral follicle development is this?
Selection
What stage in antral follicle growth is this?
dominance
Describe the follicular production of estradiol
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)
What causes ovulation/release of the oocyte?
oestradiol => LH surge => ovulation
Describe the hormonal changes from luteolysis to ovulation
Luteolysis => Decreased progesterone
Increased GnRH
Increased FSH and LH
follicular development
Increased inhibin => decreased FSH
Increased oestradiol to threshold => preovulatory LH surge => ovulation
Describe the role of PGE2 and PGF2a in ovulation
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
How does the shift from oestradiol to progesterone by the dominant follicle (due to the LH surge) lead to ovulation?
Increased progesterone => increased collagenase (dissolves collagen which occludes over tunica albuminica and basement membrane) => weakens follicular wall => ovulation
Describe the process of releasing the oocyte from a follicle
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
Describe the process of oocyte maturation after the LH surge causing ovulation
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
What causes ovulation to be induced in queens?
Nerves endings in vagina and cervix are stimulated at copulation => LH surge
