HORMONES IN REPRODUCTION II

1.   Early pregnancy:
     -     trophoblastic cells secrete HCG
     -     which signals the corpus luteum
     -     to continue its secretion of oestrogen + progesterone.














2.   Later in pregnancy:
     -     secretion of oestrogen +  progesterone
     -     is taken over by the placenta.












 3.   Progesterone + oestrogen:
     -     develop + maintain endometrium (of the uterus)
     -     throughout pregnancy.
     -     ostrogen - promotes uterine contraction, while
     -     progesterone - inhibits it.

4.   In late pregnancy - ↑ oestrogen levels increase with respect to progesterone.

5.   Prior to birth:

     -     oxytocin stimulates uterine wall contractions
     -     causing the baby to be delivered.

6.   During pregnancy:

     -     the effect of prolactin (which promotes milk production)
     -     is inhibited by high levels of oestrogen + progesterone.

7.   After birth:

     -     When ↓ oestrogen + ↓ progesterone levels drop
     -     prolactin causes the breast to produce milk

8.   The interaction between hormones:
     -     oestrogen + oxytocin
     -     and local regulators (prostaglandins)
     -     induce + regulate labour.

 

9.   Oestrogens:
     -      which reach their highest level
     -     during the last weeks of pregnancy
     -     trigger the formation of oxytocin receptors on the uterus.

10.Oxytocin:

     -     stimulates powerful contractions of the uterus.
     -     also stimulates placenta to secrete prostagladins.

11.  Prostaglandins:

     -     enhance the contractions or the uterus,
     -     making them more powerful
     -      and more frequent.

12.  Physical + emotional stresses:

      -     in turn, stimulate the release of more oxytocin + prostaglandins.

13.  This positive feedback system à underlies the three stages of labour.