ENDOCRINE CONTROL OF REPRODUCTION Flashcards
where is Gonadotrophin releasing hormone (GnRH) produced?
(in pulses) by median eminence of hypothalamus
what is pulsatile secretion?
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where does GnRH diffuse?
to pituitary & causes release of gonadotropins luteinising hormone (LH) & follicle stimulating hormone (FSH)
what does overstimulation with GnRH lead to?
to gonadotropin depletion & deficiency
what does understimulation with GnRH lead to?
to inadequate gonadotropin production & deficiency
what does FSH act on?
acts on the Sertoli cells (only)
what does FSH have an effect on?
production of (ABP) for transport of testosterone around blood effect on germ cells
what is ABP?
Androgen Binding Protein (ABP) for transport of testosterone around blood
what does LH act on?
acts on the Leydig cells
what does LH produce?
produce testosterone
what does testosterone stimulate?
germ cells directly but also acts on bone, skin, hair and the accessory sexual organs
what is testosterone converted to?
dihydrotestosterone (DHT)
what does DHT effect?
effects on prostate and oestradiol – important in epiphysial closure and reproductive system
what is FSH negatively regulated by?
by inhibin, produced by S. cells at level of pituitary
what is FSH positively regulated by?
regulated by activin & follistatin
what is LH negatively regulated by?
by testosterone acting both at level of pituitary and hypothalamus
what are the 4 phases of the ovarian cycle?
follicular phase (10-16 days)
ovulatory phase (36 hours)
luteal phase 14 days
menstruation (4-5 days)
at what phase does the greatest variability occur?
follicular phase
what does the gonadotropin releasing system do?
hypothalamic control LHRH
LH and FSH; pulsatile release
what are the ovarian hormones?
oestrogen
progesterone
what happens at follicular phase?
FSH acts on 1o and 2o follicles
causes follicular growth
promotes oestradiol secretion from follicles
FSH decreases as oestradiol rises
what does LH allow?
1o oocyte completes meiosis I produces 2o oocyte & polar body
Stops at meiosis II metaphase (fertilised)
what happens at the ovulatory phase?
oestradiol achieves threshold to switch to +ve feedback
surge of LH
oocyte matures
release of ovum
what happens at the luteal phase?
Empty 3o follicle collapses – residual granulosa cells luteinise & invade - endocrine structure - corpus luteum
Secretes oestradiol and progesterone
maintains endometrium
suppresses LH/FSH
what happens at the late luteal phase?
corpus luteum involutes oestradiol and progesterone fall endometrium not maintained (menstruation) loss of -ve feedback FSH rises begin new cycle
what happens if fertilisation occurs?
ovum implants uterus secretes hCG hCG maintains corpus luteum corpus luteum secretes oestradiol and progesterone endometrium maintained no menstruation pregnancy established
what are the effects of Oestrogens?
maintenance of bone mass effects on CNS effects on vasculature effects on lipid metabolism effects on fat distribution promote insulin secretion effects on blood clotting
what are the roles of Progesterone?
causes body temp to rise
causes change to thick cervical mucus secretion
down regulates oestrogen receptors
exerts a -ve feedback control on the hypothalamus and pituitary
what are the effects of menopause?
climacteric, mood changes, loss of libido, hot flushes
what is menopause caused by?
by decline in ovarian foll. no’s + reduced responsiveness to gonadotrophins.
Loss of oestrogen
causes increase in LH + FSH
what do the vasomotor changes in menopause cause?
hot flushes, night sweats
increased risk of coronary thrombosis
what are the other effects of menopause?
reduction in vaginal lubrication rise in pH causes discomfort
Increased risk of osteoporosis
rationale for HRT
