initiation of labour

what are the pro-pregnancy factors? (4)

- progesterone

- nitric oxide

- catecholamines

- relaxin

what are the pro-labour factors? (6)

- oestrogen

- oxytocin

- prostaglandin

- corticotrophin-releasing hormone

- cortisol

- relaxin

what is the pro-pregnancy role of progesterone?

- decreases uterine oxytocin receptor sensitivity

- which promotes uterine smooth muscle relaxation

what is the pro-labour role of oxytocin?

stimulates uterine contractions

where is oxytocin released from?

posterior pituitary gland

when is oxytocin released?

when stretch receptors in the myometrium are activated, causes release of oxytocin from posterior pituitary gland

where are prostaglandins produced? (2)

myometrium and placenta

how do prostaglandins aid labour initiation?

decrease progesterone production

where is foetal cortisol produced?

foetal adrenal glands

how does foetal cortisol aid labour initiation?

stimulates oestrogen and prostaglandin production in mother

where is corticotropin-releasing hormone (CRH) released from?

placenta

how does corticotrophin-releasing hormone (CRH) aid labour initiation?

- acts on pituitary gland of mother and foetus

- causes increased ACTH release and hence cortical production

where is oestrogen produced during pregnancy?

placenta

how does oestrogen aid labour initiation? (2)

- increases sensitivity of oxytocin receptors in myometrium to increase action of oxytocin

- stimulates release of prostaglandins

where is relaxin produced?

placenta

how does relaxin aid labour initiation? (2)

- ripens cervix

- softens pubic symphysis

what does cervical ripening involve?

- reduction in collagen

- increase in glycosaminoglycans

- increase in hyaluronic acid

- reduction aggregation of collagen fibres

what does cervical ripening cause?

reduced resistance in the cervix to the presenting part of the foetus in labour

how does oxytocin increase myometrial excitation?

increases the number of gap junctions between smooth muscle cells

what is another name for the positive feedback loop of oxytocin?

Ferguson reflex

explain the positive feedback loop of oxytocin (5)

- oxytocin stimulates uterine contraction and pushes the baby towards the cervix

- the head of the baby pushes against the cervix

- nerve impulses from cervix transmitted to brain

- brain stimulates posterior pituitary gland to secrete oxytocin

- oxytocin is carried via bloodstream to uterus

what contractions happen throughout the 3rd trimester?

Braxton Hicks contractions

what are the Braxton Hicks contractions?

'practice' contractions

what are the signs of the start of labour?

- show - mucous plug from cervix

- rupture of membranes

- regular, painful contractions