HORMONES IN REPRODUCTION I

1.   Menstrual cycle:

     -     lasts an average of 28 days
     -      controlled by the brain
     -      via hormones produced by the pituitary.

 

2.   Hypothalamus:
     -     produces GnRH
     -     which stimulates anterior pituitary
     -     to secrete FSH + LH into the blood.

3.   FSH:

     -     stimulates ovarian follicle growth
     -      which in turn secretes oestrogen.
     -      to stimulates the regrowth of the lining of uterus.

4.   Early in the cycle:

     -     low level of oestrogen ↓ à  inhibits secretion of FSH + LH  X.

5.   Middle of the cycle:

     -      high levels oestrogen ↑à stimulates a surge of FSH + LH ↑.
     -     surge of LH à triggers ovulation.
     -     ruptured follicle à develops into corpus luteum.
     -     corpus luteum à secretes oestrogen + progesterone.

 

6.   After ovulation:
     -          high levels of both oestrogen + progesterone levels to drop.

7.   At the end of the cycle:

     -     drop in ↓ oestrogen + progesterone blood levels
     -     causes uterine lining to disintegrate.
     -     frees pituitary from inhibition
     -     thus triggering the secretion of FSH + LH,
     -     which stimulates development of a new follicle.

8.   Menstrual cycle:

     -     refers to changes that occur in the uterus
     -     which begins with menstrual flow phase
     -     followed by proliferative phase,
     -     last phase - secretory phase.

9.   Ovarian cycle = running parallel to the menstrual cycle

     -     which begins with the follicular phase,
     -      followed by ovulation
     -     later, the luteal phase.

10.  Changes in the ovary + uterus:

      -     are correlated
      -     with the changing pituitary + ovarian hormone levels
      -   in menstrual cycle.