what do germ cells make indifferent supporting cells do
form granulosa cells, which surround the oocyte to form a follicle
primordial follicle
- oocyte surrounded by single layer of flattened epthelial cells
- inactive, non-growing
- stimulation to grow is independent of gonadotropin stimulation
primary follicle
- precursor granulosa cells become cuboidal
- commence mitosis
- formation of zona pellucida begins
- gap junctions between oocyte and granulosa cells
- still independent of FSH action
secondary follicle
- more layers are added
- migration of another cell to the outside of the follicle
- form a fibroblast layer around the follicle (precursor to theca interna and externa)
- formation of network of capillaries
- LH receptors
- can occur in the absence of gonadotropins, but connection to systemic vasculature signals the onset of gonadotropin depenence
antral/tertiary follicle
- pools of follicular fluid –> coalesce to form antrum
- rodents: transition from secondary to tertiary is FSH dependent
- larger animals: transition is FSH responsive but not dependent
is growth of follicles through antral stage FSH dependent or independent
dependent –> inadequate FSH leads to atresia
3 populations of cells in granulosa layer of antral follicles
- mural granulosa cells (steroids)
- antral granulosa cells (line cavity)
- cumulus cells (surround oocyte)
graadian follicles
large, mature, tertiary follicles
stages of follicular growth (3)
- preantral
- tonic
- exponential
-preantral growth phase
- entry of the primordial follicle into growing pool until it is a secondary fillicle
- FSH independent
- slow
tonic growth phase
- secondary follicle to a small antral (tertiary) follicle
- FSH responsive in larger species
exponential growth phase
- sub-population of follicles (cohort) are recruited and enter this phase
- result in a large, dominant follicle
- FSH dependent until near the end
follicle dominance
- actions of FSH are amplified by estrogen and IGF-1
- dominant follicle becomes independent of systemic (hormonal) environment
- estradoil/inhibin reduce FSH levels
- follicle can use LH in place of FSH
when are follicles vulnerable to atresia
at all stages of formation
what does follicular atresia first affect
granulosa cells –> without their support, oocyte dies
patterns of antral follicle development
- cohort of small antral follicles is recruited and grows rapidly
- selection is applied, some follicles undergo atresia
- dominant follicle(s) arise
dominant follicle development and LH
- if it develops at a time when it can trigger an LH surge, it will ovulate
- if it becomes dominant when there is still an active CL, it can’t trigger LH surge –> atresia
- allows increase in FSH and another cohort to develop
3 stages of dominant anovulatory follicular development
- active growing phase
- static phase
- regressing phase
ovulation
- gonadotropin surge starts cascade
- may be spontaneous or induced
- the result of an inflammatory cascade that weakens the follicular wall
- egg and cumulus oophorus are usually expelled within 2 minutes of follicular rupture
induced ovulation
- LH surge caused by neuroendocrine reflex activated by mating
- sensory receptors or fields must be activated
- may need several matings
- causes GnRH release –> triggers LH release
- female needs to be estrogen dominanted
