1. Hormones The menstrual cycle, pregnancy and parturition
By Charlie Grant and Harvey Davies

2. Menstrual cycle
Purpose is to produce an ovum and allow thickening of endometrium for implantation if fertilisation is to occur
Average 28 days
Uterine cycle
Day 1-7: Menses
Day 7-14: Proliferative phase
Day 15-28: Secretory phase
Ovarian cycle
Follicular (equivalent to secretory + menses)
Ovulation
Luteal (equivalent to proliferative)

3. Menstrual cycle Under hormonal control
Hypothalamic-pituitary-gonadal axis LH
Conversion of Graafian
follicle to corpus luteum,
leading to progesterone
production
Oestrogen production
FSH
Follicle development
Oestrogen secretion
Inhibin secretion

4. Menstrual cycle

5. Menstrual cycle What happens if the ovum is fertilised?
hCG produced – hCG has similar function to LH
Corpus luteum maintained
Progesterone does not fall
Menstruation does not occur

6. Pregnancy hCG Progesterone
Initially corpus luteum, then placenta at 8 weeks
Stimulates development of decidua
Prepares mammary glands for lactation
Inhibits uterine contraction
Promotes formation of mucous plug in cervical canal

7. Pregnancy
Oestrogen
Unlike progesterone, cannot be produced by placenta
Cholesterol converted to DHEA in foetal adrenal cortex
Proliferative effect on uterus and breast, including ductal structure
Aids parturition by relaxing pelvic ligaments
Helps prep uterus and cervix for labour

8. Parturition Things have to change Why does it need to change?
During pregnancy, high levels of progesterone encourage uterine gland hypertrophy and spiral artery dilation etc.
In labour, these changes are no longer important
Oestrogen encourages myometrial and breast development
Why does it need to change?
Uterus needs to become active, allowing contractions to occur
Female tract needs to be able to dilate, allowing birth

9. Oestrogen-Progesterone Switch
Reduction in the levels of progesterone, leading to a more Oestrogen dominant system
Late gestation Progesterone drop helps encourage labour to start

10. How do Oestrogen levels rise?

11. Labour

12. Labour Hormones Prostaglandins Produced ubiquitously in the body
Instigation of prostaglandin production largely based around uterine irritation and inflammation
Act directly on the myometrium to cause uterine contractions (hence why prostaglandins are used for abortions)

13. Labour Hormones Oxytocin
Secreted in high concentrations from the mother’s posterior pituitary and from the placenta
Fergusson reflex:
Babies head stretches cervix
Oxytocin release
Uterine contractions
Further stretch
[Binds to receptors on plasma membrane. Induces calcium entry, and thus contraction of myocytes - initiating contraction, and makes it efficient]

14. Labour Hormones Relaxin Relaxes structures in preparation for delivery
Has 3 main actions:
Promotes rupture of fetal membranes
Allows softening and dilation of cervix
Weakens pelvic ligaments, allowing stretch of the female pelvis

16. Questions?
Thank You