HormonesThe menstrual cycle, pregnancy and parturition

By Charlie Grant and Harvey Davies

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)

Menstrual cycle

• Under hormonal control• Hypothalamic-pituitary-gonadal axis

FSH• Follicle development• Oestrogen secretion• Inhibin secretion

LH• Conversion of Graafian follicle to corpus luteum, leading to progesterone production• Oestrogen production

Menstrual cycle

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

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

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

Parturition

• Things have 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

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

How do Oestrogen levels rise?

Labour

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)

Labour Hormones

• Oxytocin• Secreted in high concentrations from the mother’s

posterior pituitary and from the placenta• Fergusson reflex:

1) Babies head stretches cervix2) Oxytocin release3) Uterine contractions4) Further stretch

[Binds to receptors on plasma membrane. Induces calcium entry, and thus contraction of myocytes - initiating contraction, and makes it efficient]

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

Questions?Thank You