Parturition and lactation

Question 1

How often should contractions occur in the active first phase of labour

Answer 1

Regular contractions around 3 every 10 minutes

Question 2

What is the dilation at the start/end of the active first phase of labour

Answer 2

3-4cm -> 10cm

Question 3

How long does the second stage of labour last?

Answer 3

1-2 hours of strong propulsive contractions

Question 4

What hormone regulates the delivery of the placenta?

Answer 4

Oxytocin

Question 5

What hormone induces ripening of cervix

Answer 5

PGE2

Question 6

Describe the process of cervical ripening

Answer 6

As the cervix softens it can dilate/efface to become ready for labour. This process is an inflammatory one - PGE2 induces this.

Question 7

What role does COX2 have in the process of cervical ripening

Answer 7

Increased expression of COX2 in cervix at term, produces prostaglandins which cause cervical ripening

Question 8

How is the myometrium of the uterus prepared for labour

Answer 8

Oxytocin and prostaglandins cause powerful effective contractions; therefore their receptors are upregulated

Question 9

What connexin proteins are up-regulated during labour and why?

Answer 9

Cx43, Cx26; allows for better transmission of signals between cells

Question 10

What hormonal factors can influence the timing of the onset of labour?

Answer 10

Increasing oestrogen concentrations

Functional progesterone withdrawal

Question 11

At what point in pregnancy are breasts fully developed to breast feed? Why do women not lactate during pregnancy?

Answer 11

At 16 weeks the alveoli have developed; oestrogen and progesterone inhibit full lactation - the levels of both drop in post partum period allowing lactation to occur after the baby has been born

Question 12

How do prolactin levels change over the course/after pregnancy?

Answer 12

Secreted from 16 weeks but no lactation occurs due to oestrogen and progesterone inhibition.
Levels increase until birth, then after birth they drop but it is still secreted, just less of it, to allow for continued breastfeeding.

Question 13

How does suckling effect milk production?

Answer 13

Suckling stimulates the nipple, causing a neuroendocrine reflex in which VIP (vasoactive intestinal peptide) is released and dopamine release is inhibited.

Dopamine inhibits prolactin release, so if dopamine release is inhibited then prolactin release will increase.

Prolactin acts on alveolar cells in breast tissue to increase milk production.

Question 14

Describe the milk ejection reflex

Answer 14

Neuroendocrine action.
Suckling stimulates nipple, which signals to paraventricular nucleus of the hypothalamus; this induces the release of oxytocin from the posterior pituitary gland which causes the contraction of myoepithelial cells surrounding alveoli full of milk.

Milk is propelled into ducts and intramammary pressure builds up until milk is ejected through the nipple.