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