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Stage 2: Human Deveopment > Physiology of Labour > Flashcards

Physiology of Labour Flashcards

1
Q

What is the quiescence phase?

A

< 37 weeks

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2
Q

Describe the cervix and fetal membranes in the quiescence phase

A
  • Cervix intact and not contracting
  • Closed cervix maintains pregnancy and is a barrier to ascending infection
  • Membranes intact
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3
Q

What is the cervix made up of?

A

Elastic tissue with some smooth muscle, collagen fibrils in a proteoglycan matrix, epithelia cell lining and mucous plug and antimicrobial peptides to protect baby

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4
Q

What happens to the cervix and membranes in the activation and stimulation phase of labour?

A

1) Cervix ripening starts and then cervix dilates
2) Cervix softens and is more likely to dilate/efface ready for labour
3) Membrane leaking and rupture
- Inflammation

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5
Q

What inflammatory changes occur in the activation and stimulation phase of labour to change the membranes and cervix?

A
  • Inflammation breaks down fetal membranes
  • iNOS, COX2 cause production of prostaglandin (PGE2), matrix metalloproteinases 2 and 9, cytokines and immune cells
  • These promote collagen breakdown, softening of tissues, invasion of immune cells that start changing the tissue type
  • Increase in cytokines stimulates NO synthase causing production of NO and cervical dilation and softening
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6
Q

Is breaking of the fetal membranes necessary for labour?

A

No - the fetal membranes don’t have to break down for labour to begin bc some babies are born with fetal membranes intact
- Sign of labour not necessary

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7
Q

What processes initiate the inflammation leading to the changes in the cervix during labour?

A
  • Hormone changes - functional progesterone withdrawal - inflammation and influx of immune cells, increased corticotrophin releasing hormone and oestrogen
  • Cervical distension causes release of oxytocin which leads to the PGR (Ferguson reflex)
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8
Q

What is the activation phase?

A
  • Where most of the inflammation occurs
  • 1-2 weeks
  • Preparing uterus for labour
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9
Q

What is the stimulation phase?

A

Very acute phase where uterus starts contracting

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10
Q

What is used to ripen to cervix and membranes for women to go into labour?

A

PGE2 (prostaglandin)

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11
Q

What changes occur in collagen fibres near labour?

A

Collagen fibril breakdown apparent prior to labour onset

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12
Q

What happens with COX2 and PGE2 near labour?

A
  • Increased COX-2 protein in human cervix at term and postpartum
  • COX2 increases in myometrium in preparation for labour
  • COX1 stays the same
  • Up regulation of COX-2 - PG causing cervical softening
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13
Q

Describe the myometrium in the quiescence phase

A
  • Minimal uterine activity

- Myometrium is contractile but hormone suppresses contraction

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14
Q

Describe the structure of myometrium

A
  • Dense smooth muscle cells embedded in CT
  • Well vascularised
  • Sparsely innervated in pregnancy (good for pain)
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15
Q

What happens in the activation and stimulation phase to the myometrium?

A
  • Some uterine activity and then powerful effective contractions (influenced by oxytocin and PGs) - muscle is being up-regulated to contract
  • ‘Contraction associated proteins’ induced/up-regulated
  • Myometrium primed for contraction
  • Tissue itself also spontaneously contracts but needs oxytocin and PGs to make contractions stronger
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16
Q

What do substances are needed to start/make stronger uterine contractions

A

Oxytocin and prostaglandins

17
Q

What happens at the cellular level to myometrial cells?

A
  • Prostaglandin receptor, COX-2, oxytocin receptor
  • Gap junctions (connexins) between muscle cells for coordinated contraction
  • Calcium signalling proteins and ion channels - less K+ channels means the resting membrane potential is more positive making cells more excitable
  • Gap junctions form between pro-relaxation and pro-contraction myometrial cells, activating pro-contracting pathways at labour onset
18
Q

What are the two types of myometrial cells?

A

1) Pro-relaxation - suppress these pathways at labour onset, active most of pregnancy
2) Pro-contraction - attivate these pathways at labour onset

19
Q

What causes the activation and stimulation phase in the uterus?

A

1) Hormonal changes - CRH, oestrogen, oxytocin
2) Functional progesterone withdrawal - inflammation and influx of immune cells, prostaglandins from the fetal membranes
3) Uterine distension - as baby grows, uterus stretches, making it more contractile
- Same signals that target the cervix but different responses

20
Q

What drugs are used to prevent/stop pre-term labour (not v effective)?

A

1) Nifedipine - target calcium channels to block calcium channels
2) Atosiban - block oxytocin receptor to try and stop contractions
3) B2 agonists - stopped bc ineffective as cAMP pathways down-regulated during labour, side effects

21
Q

What happens with the resting membrane potential (RMP) and contraction frequency in pregnancy?

A

1) As gestation progresses, the RMP of the myometrial smooth muscle cells becomes more positive and makes it more excitable
2) As RMP increases, contraction frequency increases (contraction interval decreases)

22
Q

What is the action of oxytocin?

A

It is an important uterotonin in labour

23
Q

How does sensitivity to oxytocin change closer to labour?

A

1) Increased uterine sensitivity to oxytocin at term
2) Increased expression of oxytocin receptor mRNA and protein towards term and peak after onset of labour
3) Oxytocin receptor has increased expression closer to labour

24
Q

Describe the role of gap junctions and connexins in labour

A

1) Gap junctions made from connexin proteins - increase at end of pregnancy
2) Cx43 and Cx26 (connexin proteins) up-regulated during labour - better transmission of signals between cells
3) Increased gap junctions means increased intracellular communication and more powerful contractions

25
Q

What is the Ferguson reflex?

A
  • Spinal reflex which releases oxytocin in spurts

- Associated with nerve endings in the cervix

26
Q

When is labour induced by?

A

42 weeks

27
Q

When do most births happen?

A

Between 37 and 40 weeks

28
Q

What is the definition of pre-term birth?

A

< 37 weeks (arbitrary)

29
Q

What controls timing of birth?

A
  • Time of delivery is relatively tightly controlled
  • Both mother and fetus can affect timing
  • Women mostly deliver at night
  • Can have acute control e.g. waiting for partner, linked to stress etc
30
Q

How does timing of birth change in multiple pregnancy?

A

Often early - stress if nutrient poor or competition between twins, stretching uterus more, two placentas and 2 fetal HPA producing hormones

31
Q

What might be initiating labour in humans?

A
  • Fetal HPA axis involvement, but progesterone drop not apparent - evidence for ‘functional’ progesterone withdrawal
  • Progesterone is high but stops signalling as role of receptors change
  • Increasing oestrogen concentrations
32
Q

What happens with oestrogen and progesterone at term?

A
  • Progesterone plateaus
  • Receptors aren’t responding and rate of change of progesterone has slowed down
  • Body doesn’t detect absolute concentration of hormone but instead rate of change of hormone so as it plateaus signal pushes lower
  • Oestrogen increases so O:P ratio changes slightly even though progesterone is still very high
33
Q

Why is it hard to stop pre-term labour?

A
  • Don’t know what’s driving labour and what comes first

- Many contributory events (evolutionary sound strategy)

34
Q

What is a proposed mechanism of human labour?

A

1) Placenta grows and produces CRH and oxytocin
2) Fetus is growing causing increased cortisol from fetal adrenal gland leading to PG production in placenta increasing inflammation and affecting uterus and cervix
3) Aromatase activity - as adrenal gland gets bigger, also produces DHEAS —> placenta —> production of oestrogen (pro-contractile) and upregulates contractile proteins
4) Baby stretches, causing uterus to stretch, prepares uterus + feedback to maternal pituitary to produce oxytocin through Ferguson reflex
5) Growth of fetus also potentially sets up inflammatory response e.g. production of surfactant

Stage 2: Human Deveopment (34 decks)

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