HRR: female repro physiology I Flashcards
Describe the HPO (hypothalamic pituitary ovarian) axis
GnRH neurons secrete GnRH that binds to GnRHR1 in the median eminence. Gonadotrophs in the anterior pituitary produce FSH and LH. FSH and LH stimulate the ovaries to produce estradiol and progesterone.
What is the hypothalamic kisspeptin system?
Key modifier of GnRH neurons and secretion; hypothalamic neurons release Kiss-1 to alter GnRH neuronal activity.
What is GnRH pulsatility?
GnRH neurons release GnRH in a pulsatile fashion. This is important for proper receptor expression/upregulation.
What happens if GnRH is not released in a pulsatile fashion?
Receptor expression will not be at the optimal level or receptors will not be expressed at all.
High frequency GnRH pulses favor ___ release
LH
Low frequency GnRH pulses favor ___ release
FSH
What do long-acting GnRH agonists do?
Reduce LH and FSH via continuation of pulses desensitizing receptors.
What are inhibins?
Produced by granulosa cells in the ovary that are stimulated by FSH release and serve to shut down FSH secretion from the pituitary once a certain level is reached.
Describe midcycle positive feedback.
In the middle of the ovulation cycle (day 11), there is a surge in estradiol as it is not controlled by negative feedback anymore and becomes a more positive-feedback system. This leads to an LH surge and ovulation!
What happens to GnRH pulsatility in the mid-cycle?
The pulses and amplitude are increased; this is what leads to disproportionate LH increase compared to FSH.
What happens in the luteal phase in terms of the hypothalamic pituitary ovarian axis?
Progesterone is released that sends negative feedback to the pituitary and hypothalamus, largely via inhibins. The LH surge is over!
When is the peak for oocytes in females?
Around 6 months in utero! It declines after that.
What is a primordial follicle?
Small oocyte arrested in prophase I.
What is a primary follicle?
Growing oocyte surrounded by 1 or 2 layers of granulosa cells.
What is a secondary follicle?
Oocyte with 2 or more layers of granulosa cells and an array of theca cells.
What is a graffian follicle?
A mature follicle with fluid-filled antrum; once the theca interna is visible here, steroid production can occur.
The presence of a mature antrum indicates…
Expression of steroidogenic genes like StAR.
What is corpus luteum?
After ovulation, the dominant follicle changes histologically to become the corpus luteum. The cells enlarge, proliferate, vascularization occurs. Major source of sex steroid production following ovulation.
What controls formation of corpus luteum?
LH.
What are the steps of the ovarian cycle?
- Folliculogenesis (primordial/primary follicle) 2. Secondary follicle formation 3. Dominant follicle 4. LH surge/ovulation 5. Corpus luteum formation.
Formation of a secondary follicle is ___ dependent.
LH and FSH.
When does production of androgens, estrogens, and steroidogenic genes begin?
With the secondary follicle formation.
Maintenance of steroid production by the CL requires…
Continued LH stimulation.
Thecal cells produce which hormone class?
Androgens.
What steroid classes are secreted by ovaries?
Estrogens, progestin, androgens.
Granulosa cells produce which hormone class?
Estrogens.
Describe how granulosa cells are able to form estrogens.
- LH increases StAR action/transcription and desmolase in thecal cells. 2. Thecal cells produce androgens. 3. Androgens diffuse into granulosa cells. 4. Aromatase forms estrogens from androgens with the help of FSH stimulation.
___ is necessary for thecal production of androgens, while ___ is necessary for granulosa production of estrogen in the follicular phase.
LH, FSH.
What hormones are formed in the follicular phase?
Androgens and estrogens.
What is the key hormone formed in the luteal phase?
Progesterone.
What do granulosa cells gain in the luteal phase?
LH receptors and StAR.
What is the significance of granulosa cells gaining LH receptors in the luteal phase?
It gives them the ability to utilize StAR; this allows for the granulosa cells to make progesterone in addition to making estrogens.
What is antimullerian hormone?
Made by the fetal testes and granulosa cells of small growing follicles; correlates with number of developing follicles and can be a marker of fertility.
Describe FSH in the days preceding menstruation.
There is a slight bump in FSH levels due to lower E2, progesterone, and inhibins. This FSH is responsible for selecting the next follicle to become the dominant follicle.
Inhibin B is secreted by ___ cells.
Granulosa.
What is inhibin B an indicator of?
Size and growing cohort of follicles.
Inhibin A is secreted by ___ cells.
CL.
Inhibin production is under ___ control.
FSH.
