Session 2 - Control of reproductive processes Flashcards
What are the glycoprotein hormones that the ant pit secretes? What cell type produces each hormone?
FSH – produced by gonadotrophs
LH - produced by gonadotrophs
TSH - produced by thyrotrophs
What are the polypeptide hormones that the ant pit secretes? What cell type produces each hormone?
GH - produced by somatotrophs
ACTH - produced by Corticotrophs
Prolactin - produced by lactotrophs
What are the hormones that the post pit produces?
ADH Oxytocin (important for reproduction)
How is gonadotrophin secretion controlled by the hypothalamus? What is the releasing hormone of FSH and LH?
- Anterior pituitary secretion controlled by hypothalamus via releasing hormones
- These travel in hypophyseal portal circulation
- Releasing hormones released by neurosecretory neurons.
- Arterial blood arrives in hypothalamus, picks up releasing hormones and moves onto into hypophyseal portal circulation to the anterior pituitary (therefore don’t need to secrete much hormone as it doesn’t get diluted due to direct blood supply).
- Releasing hormone is GnRH
what is the nature of FSH and LH release?
puslatile - once an hour
What are the actions of FSH and LH?
steroidogenesis, gonadal growth, gametogenesis
What influences GnRH secretion?
- Feedback from gonads - inhibited by steroids
- Environmental effects, body weight
What is the action of GnRH in males? What is the action of FSH and LH? What is inhibin secretion rate related to? What else can affect the production of testosterone?
- Testosterone reduced GnRH secretion
- Spermatogenesis occurs continuously and male must be ready for action at any time. Therefore, hormone levels constant in medium and long term, achieved by –ve feedback
- FSH binds to Sertoli cells
- LH binds to Leydig cells:
- Promotes testosterone release and spermatogenesis
- Inhibin secretion related to rate of spermatogenesis.
- Testosterone is higher in mornings due to circadian rhythms and can be affected by environmental stimuli
What happens to GnRH under:
a) moderate amounts of oestrogen secretion
b) high amounts of oestrogen alone?
c) progesterone?
a) Moderate amounts – reduce GnRH secretion, reduces amount of GnRH per pulse
b) High amounts ALONE – Promote GnRH secretion, promotes LH surge
c) Prevents positive feedback of high oestrogen
Increases inhibitory effects of moderate oestrogen
Reduces frequency of GnRH pulses
What does inhibin do in both sexes? What is inhibin secretion related to?
Inhibin from gonad reduces FSH secretion
Inhibin secretion related to developing gametes - More developed gametes release more inhibin
What are the 3 phases of the menstrual cycle?
Follicular, ovulation, luteal
What is the action of FSH and Lhg in the follicular phase? What does oestrogen stimulate during this phase?
FSH binds to granulosa cells
LH binds to thecal cells (of theca interna)
Stimulates development of follicle
Oestrogen in this phase stimulates:
Fallopian tube function
Thickening of endometrium
Growth and motility of myometrium
Thin alkaline cervical mucus
Vaginal changes
Calcium metabolism
What is the action of LH pre-ovulation?
- LH surge stimulates ovulation.
- LH surge weakens theca externa and allow ovum to burst through
What is the action of LH during the luteal phase? What about progesterone? How do progesterone only contraceptives function?
LH maintains corpus luteum
Progesterone in this stage acts on oestrogen primed cells:
Further thickening of endometrium
Thickening of myometrium
Thick, acid cervical mucus – barrier against sperm and bacteria between uterus and vagina. This is how progesterone only contraceptives work.
Changes in mammary tissue
At the beginning of the menstrual cycle, what are the levels of progesterone and oestrogen? What happens here?
Low progesterone and oestrogen
FSH levels rise:
- Binds to granulosa cells
- Theca interna develops
- Secretes oestrogen stimulated by LH
- Secretes inhibin
What happens in the mid follicular stage?
- Oestrogen levels rising
- Inhibin levels rising – inhibit FSH, no new follicles can develop
- Oestrogen exerts +ve feedback at hypothalamus and pituitary
- LH levels rise but not FSH
What happens in the pre-ovulatory phase?
LH surge. Precise timing may be influenced by environmental factors
What happens after ovulation?
Corpus luteum spontaneously forms:
- Begins to secrete progesterone and oestrogen
- Maintains suppression of FSH
- LH also suppressed because +ve feedback inhibited by progesterone
How long does the luteal phase last? What happens during it?
- Corpus luteum grows and secretes more steroids
- After 14 days it dies
What happens if there is no pregnancy after the luteal phase?
- Death of corpus luteum
- Rapid fall in steroid levels
- Stimulates menstruation
- Relieves inhibition of FSH
What happens after the luteal phase if there is a preganancy?
If pregnancy occurs, HCG released by placenta preserves corpus luteum. Corpus luteum secretes increasing amounts of steroids but placenta soon secretes even more and after 12 weeks corpus luteum no longer supports pregnancy.
Why does the menstrual cycle vary in length? How many days is it from ovulation to menses?
Variation in timing of ovulation. From ovulation to menses always takes 14 days
What happens to hormone levels after menopause and why?
Ovary secretes less oestrogen so levels of FSH, LH and GnRH rise.
FSH increases more than LH because there is no inhibin secreted from ovary.
How does prolactin suppress fertility?
Supresses FSH and GnRH
