57.4 Birth and lactation

Question 1

What is the onset of labour marked by?

Answer 1

regular, painful uterine contractions and progressive dilation of the cervix

Question 2

What is the first stage of labour?

Answer 2

the time from onset to full cervical dilation. Uterine contractions become progressively stronger to propel the foetus down the birth canal. At the same time, the amniotic sac ruptures (‘waters break’)

Question 3

What is the second stage of labour?

Answer 3

the time from full cervical dilation until birth. It usually lasts 40–60min

Question 4

What is the third stage of labour?

Answer 4

the time from birth to the delivery of the placenta. Ergometrine, a smooth muscle stimulant, is often administered to enhance contractions and promote placental delivery (afterbirth).

Question 5

Describe the mechanical process of parturition

Answer 5

Myometrial contractions begin from uterine fundus and squeeze baby towards endocervix for delivery

Question 6

What are the roles of prostaglandins in parturition?

Answer 6

• cervical ripening (hormonal softening of the cervis prior to the onset of labour contractions)
• membrane rupture (amniotic sac breaks open)
• myometrial contractions

Question 7

What is the role of oestrogen in parturition?

Answer 7

Stimulates development of contractile proteins and oxytocin receptors (more contraction, more oxytocin)

Question 8

What is the role of oxytocin in parturition?

Answer 8

(Gq linked) - Increases myocyte calcium levels to induce contraction
*Oxytocin secretion is stimulated by uterine distension and vaginal stimulation as the foetal head descends which, in turn, stimulates more oxytocin release (positive feedback—the Ferguson reflex).

Question 9

Why are there gap junctions between myometrial cells?

Answer 9

ensure a rapid spread of contractions

Question 10

What is the role of PGF2α in pariturition?

Answer 10

PGF2α (stimulated by oxytocin) is synthesized by the myometrium and stimulates muscle contraction and cervical ripening (cervix softens and dilates). Labour can be induced at term using vaginal pessaries containing PGF2α.

Question 11

Why is pre-term delivery dangerous?

Answer 11

Foetus is not prepared for extrauterine life

Question 12

What is the uterine role of progesterone?

Answer 12

Relaxant, prevents premature delivery

Question 13

What is the Ferguson reflex?

Answer 13

A neuroendocrine reflex of a self-sustaining cycle of uterine contractions

Question 14

Describe the mechanism of the Ferguson reflex

Answer 14

• Foetal head stretches cervix
• Sensory fibres send signals to hypothalamus - stimulates oxytocin release
• Oxytocin receptors in myometrium activated –> more contractions
• More stretch

Question 15

Which hormone controls milk production?

Answer 15

Prolactin

Question 16

Which hormone controls milk ejection?

Answer 16

Oxytocin

Question 17

What is the action of oestradiol, progesterone and hPL on the breasts during pregnancy?

Answer 17

• Whole gland undergoes hypertrophy
• Ducts dilate
• Milk-secreting alveoli mature
• Additional adipose tissue laid down

Question 18

Which hormones must fall for lactation to occur?

Answer 18

Steroid hormones - i.e. osterogen/progesterone
Which occurs after placental delivery

Question 19

What stimulus increases prolactin secretion?

Answer 19

Suckling on breasts

Question 20

What is particular about the control of prolactin secretion?

Answer 20

Only pituitary hormone which can be controlled by inhibition by dopamine

Question 21

What is the actual hormonal effect of suckling (in terms of prolactin)?

Answer 21

Fall in output of dopamine

Question 22

Describe the mechanism of the milk ejection (let-down) reflex

Answer 22

• Baby suckles
• Signals to hypothalamus to increase synthesis and secretion of oxytocin
• Oxy stimulates contraction of myoepithelial cells in alveoli
• Contents of alveolar lumen squeezed out into lactiferous ducts
• Intramammary pressure rises –> milk ejection

Question 23

What causes lactational amenorrhea?

Answer 23

*High levels of prolactin suppress menstrual cycle
*Daily suckling stimulus reduces the pulsatile release of GnRH. This is probably the mechanism by which lactation can act to suppress fertility

Question 24

What is the role of foetal cortisol in parturition?

Answer 24

Foetal cortisol initiates a switch in the placenta away from progesterone synthesis to oestrogen synthesis in the last few days of pregnancy. Oestrogens, together with oxytocin and prostaglandin F2α (PGF2α), increase the contractility of the myometrium to bring about delivery

Question 25

What is normal term for pregnancy?

Answer 25

40 weeks after last menstrual period

Question 26

Why is post term parturition hazardous?

Answer 26

continued foetal growth and placental insufficiency pose problems for both delivery and foetal nutrition

Question 27

What changes must occur in the foetus in preparation for post-natal life that may not have occurred in pre-term babies?

Answer 27

• Production of surfactant in the lungs to allow lung expansion when air is first breathed
• Changes to gut and liver enzymes to allow the foetus to metabolize its postnatal milk diet

Question 28

When is post-term labour usually induced by?

Answer 28

42 weeks

Question 29

What is lactation?

Answer 29

synthesis and secretion of milk by the mammary gland.

Question 30

How can parturition be induced?

Answer 30

• Physical separation of the amniotic sac from the cervix by an obstetrician or midwife (a sweep)
• Application of prostaglandin cream/gel on the cervix to encourage dilation
• Oxytocin can be administered to help induce myometrial contractions
• Rupture of the membranes (also known as breaking of the waters), → an increase in prostaglandin release, which accelerates development of full contractions.

Question 31

Describe the structure of the mammary glands at different developmental stages

Answer 31

Question 32

What can hypersecretion of prolactin by pituitary tumours lead to?

Answer 32

galactorrhoea and infertility

Question 33

What is galactorrhoea?

Answer 33

spontaneous milk ejection not associated with childbirth or nursing