5 - Repro - Control of Reproductive Processes Flashcards
From where is GnRH secreted?
Hypothalamus
How is GnRH transported to the anterior pituitary?
Hypophyseal portal system
Define portal system:
Vascular arrangement where blood from a capillary bed is transported to another capillary bed, via connecting veins
What type of cells in the anterior pituitary does GnRH act on?
Gonadotropes
How do the gonadotropes respond to GnRH?
Secrete FSH + LH
Why does oestrogen levels increase towards ovulation?
As the follicle grows, more oestrogens are secreted in response to a given gonadotropic stimulation
Why does progesterone and oestrogens increase after ovulation?
As the corpus luteum grows, more progesterone and oestrogens are secreted in response to a given concentration of LH
Leydig cells in the testes bind LH. What is the effect of this?
LH stimulates Testosterone production from Leydig cells
How does FSH affect Sertoli cells?
Maintains them and makes them responsive to Testosterone
Approx. how much testosterone is secreted by Leydig cells per day?
~ 4-10 mg/day
Which hormones produced by the gonads REDUCE GnRH secretion?
- Testosterone
- Oestrogen (at moderate concentrations)
- Inhibin
How does Oestrogen (at moderate concentrations) affect GnRH secretion?
Reduces GnRH secretions from the hypothalamus
- Reduces the amount of GnRH released per pulse
Why can the LH surge only occur at low concentrations of progesterone?
Progesterone inhibits oestrogen from having a positive feedback affect on the hypothalamus. This positive feedback causes a GnRH surge, which results in the LH surge from the anterior pituitary.
Which cells secrete inhibin?
- Females = granulosa cells
- Males = Sertoli cells (when spermatogenesis occurs too rapidly)
What is meant by a ‘determinative’ effect of testosterone?
An effect which is only partly reversible, if at all (non dependent on continuous production of testosterone)
- most secondary sex characteristics are ‘determinative’ effects, ie deepening of voice
What is meant by a ‘regulatory’ effect of testosterone?
An effect which is reversible, and dependent of continuous production of testosterone.
- ie maintenance of internal genitalia, aggression and sexual activity
What are the 2 phases of the ovarian cycle?
- Follicular phase
- Luteal phase
High concentrations of oestrogen cause a GnRH surge, resulting in an LH surge. Why doesn’t FSH concentrations also increase?
Granulosa cells secrete inhibin, which suppresses FSH release
On which day of the menstrual cycle does the concentration of LH peak?
Day 13
On which day of the menstrual cycle does the concentration of progesterone peak?
Day 21
What are the 3 stages of the endometrial cycle?
- Menses
- Proliferative phase
- Secretory phase
Which main hormonal change causes menses to occur?
Sudden drop in progesterone (+ oestrogen)
Which main hormonal change causes the proliferative phase of the endometrial cycle?
Increasing concentration of oestrogen
Which main hormonal change causes the secretory phase of the endometrial cycle?
Increasing concentration of progesterone
