57.4 Birth and lactation Flashcards
What is the onset of labour marked by?
regular, painful uterine contractions and progressive dilation of the cervix
What is the first stage of labour?
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’)
What is the second stage of labour?
the time from full cervical dilation until birth. It usually lasts 40–60min
What is the third stage of labour?
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).
Describe the mechanical process of parturition
Myometrial contractions begin from uterine fundus and squeeze baby towards endocervix for delivery
What are the roles of prostaglandins in parturition?
- cervical ripening (hormonal softening of the cervis prior to the onset of labour contractions)
- membrane rupture (amniotic sac breaks open)
- myometrial contractions
What is the role of oestrogen in parturition?
Stimulates development of contractile proteins and oxytocin receptors (more contraction, more oxytocin)
What is the role of oxytocin in parturition?
(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).
Why are there gap junctions between myometrial cells?
ensure a rapid spread of contractions
What is the role of PGF2α in pariturition?
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.
Why is pre-term delivery dangerous?
Foetus is not prepared for extrauterine life
What is the uterine role of progesterone?
Relaxant, prevents premature delivery
What is the Ferguson reflex?
A neuroendocrine reflex of a self-sustaining cycle of uterine contractions
Describe the mechanism of the Ferguson reflex
- Foetal head stretches cervix
- Sensory fibres send signals to hypothalamus - stimulates oxytocin release
- Oxytocin receptors in myometrium activated –> more contractions
- More stretch
Which hormone controls milk production?
Prolactin
Which hormone controls milk ejection?
Oxytocin
What is the action of oestradiol, progesterone and hPL on the breasts during pregnancy?
- Whole gland undergoes hypertrophy
- Ducts dilate
- Milk-secreting alveoli mature
- Additional adipose tissue laid down
Which hormones must fall for lactation to occur?
Steroid hormones - i.e. osterogen/progesterone
Which occurs after placental delivery
What stimulus increases prolactin secretion?
Suckling on breasts
What is particular about the control of prolactin secretion?
Only pituitary hormone which can be controlled by inhibition by dopamine
What is the actual hormonal effect of suckling (in terms of prolactin)?
Fall in output of dopamine
Describe the mechanism of the milk ejection (let-down) reflex
- 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
What causes lactational amenorrhea?
*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
What is the role of foetal cortisol in parturition?
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
What is normal term for pregnancy?
40 weeks after last menstrual period
Why is post term parturition hazardous?
continued foetal growth and placental insufficiency pose problems for both delivery and foetal nutrition
What changes must occur in the foetus in preparation for post-natal life that may not have occurred in pre-term babies?
- 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
When is post-term labour usually induced by?
42 weeks
What is lactation?
synthesis and secretion of milk by the mammary gland.
How can parturition be induced?
- 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.
Describe the structure of the mammary glands at different developmental stages
What can hypersecretion of prolactin by pituitary tumours lead to?
galactorrhoea and infertility
What is galactorrhoea?
spontaneous milk ejection not associated with childbirth or nursing
