Reproduction and Sex Steroid Axis 2 Flashcards
compare the structures of LH and FSH
identical a subunits but specific ß subunits
outline male physiology
pulses of GnRH are released from the hypothalamus which stimulate LH and FSH release from the pituitary
what does LH do in males
stimulate testosterone production from the Leydig cells of the testes
testosterone action
produce appropriate tissue responses: male 2y sexual characteristics, anabolism and maintenance of libido
acts locally within testes to aid spermogenesis
feeds back to hypothalamus/pituitary to inhibit GnRH secretion
how does testosterone circulate in body
largely bound to SHBG
what does FSH do in males
stimulates the Sertoli cells in the seminiferous tubules to produce mature sperm and inhibins A and B
inhibins feed back to the pituitary to decrease FSH secretion
what counteracts inhibin
activin
where is GnRH produced
arcuate nucleus in the hypothalamus
low and high frequency pulses - LH and FSH
low frequency stimulate FSH, high stimulate LH
what does LH do in females
stimulates ovarian androgen production by the ovarian theca cells
what does FSH do in females
stimulates follicular development and aromatase activity in ovarian granulosa cells
stimulates the release of inhibin from ovarian stromal cells, which inhibits FSH. Counteracted by activin
aromatase activity
enzyme that converts androgen to oestrogen
mean duration of menstrual cycle
28 days
average duration of menses
3-8 days
when does ovulation normally occur
mid cycle - day 14
normal estimated blood loss in menstruation
30ml
follicular growth
- begins when oestrogen levels are low - provides feedback for FSH and LH secretion which stimulates follicles to develop
- one leading follicle develops by day 8-10
- granulosa cells around the egg enlarge and release oestrogen - this negatively feedbacks to the pituitary causing it to produce less FSH, meaning there is only enough to stimualte one follicle
when in the menstrual cycle does ovulation occur
- enlarged granulosa cells causes oestrogen levels to rise, this makes the pituitary more responsive to GnRH - LH surge
- after the LH peak the oocyte is released: collagen wall of the follicle is digested and it ruptures releasing the ova into the Fallopian tubes
- where it waits to be fertilise by une sperm
luteal function phase
secretory phase that starts after ovulation
beigns with the formation of the corpus luteum from remaining granulosa cells
this releases oestradiol and progesterone by the action of 3ß-HSD
when is peak progesterone production noticed
one week after ovulation takes place
what happens to the CL in the absence of pregnancy
luteolysis - progesterone levels drop, uterine lining detaches and menstruation begins
In pregnancy, the CL continues to release oestradiol and progesterone maximizing the chance of implantation into the endometrium.
what is in the discharge in menstruation
tissue, blood and unfertilized egg
how does an ovulation predictor kit work
detects the LH surge, 36 hours before ovulation
what effect does progesterone have on temperature
thermogenic - increases basal body temperature during ovulation
