Lecture 15 + 16 - 2018/2017 Flashcards
Define labour?
Getting the fetus from the uterus to the outside world i.e. uterine activity and cervical change which leads to the expulsion of the fetus and placenta. Labour is also prevention of haemorrhage so that the mother survives and is able to establish lactation to nurture the newborn.
What are the three P’s of anatomy and physiology of labour?
- Power - the forces that drive the baby out.
- Passage - the birth canal that the baby comes through.
- Passenger - the baby.
What are the challenges in human parturition?
- Quiescence - of uterus with growth, distension, pressure.
- Timing - for safe birth.
- Activation - stimulation of uterine musculature changes in genital tract.
- Birth - fetal-neonatal adaptations.
- Involution - haemostasis, establishing lactation.
How does a pregnant women maintain quiescence?
Typically the uterus is contracting all the time, but during pregnancy the contractions are:
- weak and poorly coordinated.
- low amplitude (<10mmHg).
- low frequency.
- painless.
- cervix is firm and closed.
What happens physiologically in quiescence?
Hormones such as: -Progesterone. -PGI2. -Relaxin. -PTHrP. -Nitric Oxide (NO) all cause there to be an increase in cyclic nucleotides which causes there to be a decrease in calcium and MLCK, which causes quiescence.
What happens if there is withdrawal of 1 or more of the substances?
It can cause quiescence to stop - baby can be released early.
What is labour triggered by?
Typically it is triggered by withdrawal of progesterone - it is a functional drop.
How is progesterone involved in quiescence?
Progesterone reduces prostaglandin F synthesis, it affects calcium transport and it increases beta-adrenergic receptors.
What determines gestation length (time that baby is in belly)?
- Parity.
- Age.
- Genetics (maternal and paternal).
- Race-ethnicity (african/asian = 39 weeks, caucasian = 40 weeks).
Can stress affect gestation length?
Stress (steroid hormones or cytokines) can influence the length of gestation - social factors as well as medical. Extreme stress may cause early gestation.
When does parturition typically occur?
280 days from LMP (37-42 weeks) OR 268 days from conception.
What does activation involve?
- Fetal genome - have to have intact fetus.
- Uterine stretch/growth - the uterus cannot stretch forever i.e. twins can cause a shorter pregnancy.
- Fetal HPA axis - anencephaly can cause the pregnancy to go on longer.
- Up-regulation of myometrium - an increased contraction of myometrium due to increased CAPs.
- Melatonin and circadian rhythms - more babies delivered at night than day.
- Abnormally - if membranes rupture pre-labour.
Describe activation - up regulation of myometrium?
There is an increase in CAPs (gap junctions - connexin 43). There is an increase in connexin 43 (gap junctions).
What are CAPs?
Contraction associated proteins that form gap junctions - connexin 43 - which link the muscles of the myometrium together.
What do CAPs do?
- Increase myometrial contractility (actin/myosin).
- Increase myocyte excitability of ion channels (calcium voltage regulated).
- Increase in intercellular connectivity gap junctions multimers of cx43.
How do you stop an increase in myometrial activity during activation?
Use calcium channel blockers such as nifedipine.
How do you stop an increase in myocyte excitability ion channels (calcium voltage regulated)?
Use beta-2 sympathomimetics e.g. salbutamol.
How do you stop an increase in intercellular connectivity gap junctions multimers of cx43?
Use prostaglandin synthase inhibitors (COX1 and COX2) e.g. paracetamol.
What role does prostaglandin have in labour?
- Increases myometrial contractility.
- Lead to cervix changes.
- Associated with membrane rupture.
How do we use prostaglandins to stimulate labour?
We use PG analogues such as PG gel (e.g. misoprostol). Or we can put a finger through the cervix to cause tissue trauma to start labour.
What is oxytocin?
Non-apeptide from the posterior pituitary and genital tract.
Describe how oxytocin is used in labour?
Oxytocin is not essential for the initiation of labour, it is used to continue labour (augment). It is also used to prevent post-partum haemorrhage.
What does oxytocin require?
Gap junctions to be effective - it requires the muscle fibres to be connected.
What is the cervix (in labour)?
The barrier between the outside world and the baby. During pregnancy the cervix is closed and tight, and during labour the cervix is open.