11 puberty, secondary sexual characteristics, menstrual cycle, contraception Flashcards
what are the 6 major hormones, where are they released from?
what type of hormones are they on a molecular level?
- Gonadotrophin releasing hormone (GnRH)- hypothalamus, decapeptide
- FSH- ant pituitary . two glycosylated proteins
- LH- ant pituitary. two glycoslated proteins
- oestradiol- ovary. steroid
- progesterone-ovary. steroid
- testosterone- testis, adrenal gland, ovary. androgen
oestrogens=?
oestradiol+ oesterone
how does GnRH travel to the anterior pituitary?
via hypothalamo-pituitary portal vessels
days 0-14 of menstrual cycle in terms of GnRH, FSH, LH, oestradiol
- surge in GnRH stimulates secretion of FSH and LH-> act on ovary
- FSH act on follicle causing oestradiol to be produced on granulosa cells -> -ve feedback on ant. pituitary (LH also stimulates oestradiol)
- -ve feedback causes drop in LH and FSH in first half of cycle
effects of LH and FSH days 0-14
FSH: acts on granulosa cells on follicle to increase synsthesis of oestradiol
LH: act on thecal cells on follicles to produce androgens
what is cholesterol used to produce
- androgens
- oestrogens (from androgen)
- glucocorticoids and mineralocorticoids in adrenal cortex
what can be used to treat breast cancer
block conversion of testosterone to oestrogens
what cells do LH bind to in the synthesis of oestradiol?
what reaction does this cause?
- LH binds to receptors on thecal cells
- cholesterol-> androstendione
why must androstendione be produced on thecal cells and not on granulosa cells?
granulosa cells do not have enzymes to produce androstendione
what type of activity allows the formation of oestradiol from andostenedione?
aromatase activity when FSH binds to receptors on gransulosa cells
which receptors do thecal and granulosa cells contain?
thecal cells only have receptors for LH
granulosa cells have FSH and then switch to LH
day 0-14: why do oestradiol levels rise when FSH and LH levels drop?
oestradiol increases proliferation of granulosa cells -> more oestradiol produced -> bind to receptors on granulosa cells
positive feedback
ovulation: what do high oestradiol levels cause in late follicular stage? at mid cycle
act on pituitary to release more LH (via GnRH)
at mid cycle -ve feedback becomes positive to allow a short surge of LH
what happens to granulosa cells at mid cycle?
- high oestradiol and FSH causes change of action of LH
- stimulate LH receptors on granulosa cells
- increasing progesterone synthesis
what is the dominant hormone in the second half of cycle?
how does this come about?
progesterone
presence of high LH and cholesterol converted to progesterone on granulosa cells
corpus luteum - what is it formed by?
how is maintained?
what does it secrete?
how many days is the life of CL if not pregnant?
- formed by collapsed follicle
- maintained by LH
- secrete progesterone (maintain endometrium)
- oestradiol levels begin to drop (progesterone inhibits oestradiol synthesis)
- low levels of LH maintain CL. life of CL in non pregnant is 14 days
what happens to hormones in days 14-28?
GnRH
FSH and LH
- progesterone causes a decrease in gonadatrophin secretion (suppress GnRH secretion- decrease in oestradiol levels also decrease GnRH)
- FSH and LH levels are low so no new follicles develop
death of corpus luteum
- Corpus luteum degenerates (due to production of PGF2a)
- Decrease in progesterone and oestradiol levels
- Increase in FSH and LH levels allow new follicles to mature
- Onset of menstruation
how does hormonal contraception suppress ovulation?
- Suppress ovulation by negative feedback of progesterone on the pituitary and hypothalamus
- Decrease in GnRH secretion resulting in low FSH and LH levels – no new follicles develop
cessation of menstrual cycle in pregnancy
- No menstrual cycle occurs as high levels of progesterone are present.
- Inhibit secretion of pituitary gonadotrophins
- CG secreted by trophoblast cells.
what do low concentrations of oestradiol cause on LH before 10 days of menstrual cycle? how does this differ after 10 days?
negative feedback on LH at low conc
positive feedback on LH at high conc after 10 days
what happens at ovulation?
oocyte release
recruitment of 5-9 new follicles
