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MBCHB3: Reproduction, Development and Ageing > Lecture 15: Normal Birth > Flashcards

Lecture 15: Normal Birth Flashcards

1
Q

What are the two components that define labour:

A

Uterine activity and cervical change which leads to the expulsion of the fetus and placenta

Contraction (uterine) + Shortening + Dilation (Cervical)

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2
Q

What are the key players of parturition?

A

Uterus
Cervix
Hormones

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3
Q

Why is the uterus amazing?

A
  • Relaxed & quiescent - but massive growth
  • Decides when to start labour
  • Highly coordinated, forceful activity (but with relaxation to allow sustained blood flow)
  • Remains contracted (allows sufficient tension on cervix)
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4
Q

What are the layers of myometrium?

A 
Outer layer (long. fibres)
Middle layer (mesh-like fibres)
Inner layer (circular fibres)
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5
Q

Describe the structure of myometrium: what enhances or decreases contractile force:

A

Interaction between actin and myosin filaments cause contraction (Ca dependent)

Oxytocin and prostaglandins promote Ca uptake into cell / freeing from intracellular stores

Progesterone, cAMP, b adernergic agents inhibitory

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6
Q

What triggers myometrial activity:

A

Myometrium is spontaneously active smooth muscle, produce regular contractions without hormonal or nervous input

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7
Q

Myocyte contraction are phasic in nature, describe what influences this:

A
  • Resting tone with cycles of discrete, intermittent contractions
  • Varying frequency, amplitude and duration
  • Contractions are modulated by
  • > Cell surface receptors

Coordination of contractions facilitated by GAP junctions

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8
Q

Describe the effect of progesterone, estrogen, oxytonin, prostaglandins on the uterus:

A

Progesterone, prostaglandins (PgI2) is a relaxant.

Estrogen, oxytonin, prostaglandins (PgE2, F2) are all uterotonic.

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9
Q

What are the physiological processes of labour:

A

Quiescence -> Activation -> Stimulation -> Involution

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10
Q

What are the anatomical changes associated with physiological processes of labour:

A

Quiescence: Myocyte hyperplasia/trophy. Ligametns laxity, cervix softens

Activation: Lower segments form

Stimulation: Cervix shortens and effaces, membranes rupture, coordinated uterine activity.

Involution: Retraction, remodelling

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11
Q

Describe the changes of the uterus in pregnancy:

A
  • Myometrium is tranquil
  • Increase in capacity (volume)
  • First weeks of pregnancy: Myometrial hyperplasia - then, from stretch-induced myometrial activity
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12
Q

Describe the physiological changes seen in quiescence:

A
  • Uterine contractions poorly synchronised.
  • Low amplitude
  • Low Hz, ‘painless’ Braxton Hicks
  • Cervix softens but remains firm and closed
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13
Q

What factors contribute to quiescence:

A

Progesterone is the major contributor

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14
Q

What is the goal of activation in labour?

A

Priming for labour

  • Myocytes becomes more responsive
  • Occurs without servical change
  • Last 6-8 weeks of pregnancy
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15
Q

Myocytes become more responsive in the physiological process known as activation in labour, describe the upregulation of myometrium-1 and how this contributes:

A

Increase in contractile associated proteins (CAPS)
i.e oxytocin and Pg receptors
CAPS control contractility of myocytes
- Enhanced interactions between actin and myosin
- Increase excitability of ind. cells
- Promote crosstalk between muscle cells

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16
Q

Myocytes become more responsive in the physiological process known as activation in labour, describe the upregulation of myometrium-2 and how this contributes:

A
  • Gap junctions allow AP to propogate through myometrium

- Many types by connexin 43 most important

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17
Q

Whats the role of progesterone in labour?

A

Maternal/fetal/amniotic conc. elevated through birth

  • > Removing CL and thus Prog actually induces preg. loss
  • > Prog. treatment from early (but not late) pregnancy can reduces rates of PTB in well selected women
  • > Giving progesterone antagonist causes cervical effacement and labour…

Progesterone promotes myometrial relaxatation and quiesence. Therefore its withdrawal is essential for all functions. But must be timed.

18
Q

What is the role of oxytocin?

A
  • Not essential for induction of labour
  • Its conc. doesnt actually change, but there is a 200 fold increase in receptor concentration. It promotes contraction of myometrium.
19
Q

What is the role of estrogen in labour?

A
  • uterotonic but does not directly cause contractions.
  • Upregulates gap junctions and uterotonic receptors. (inc. oxytocin)
  • Estrogen produced in placenta, but placenta lacks precursors (fetal adrenals provide abundant DHEAS)
    = Fetus has role in myometrial priming and sitmulation
20
Q

What is the role of prostaglandins and labour?

A

PG E2/F2 uterotonic / cervical ripening.

Its likely to contorl the final pathway of onset of labour.

  • > Increase in uterine synthesis at onset
  • > Administration results in labour
  • > Inhibition of PG synthesis suppresses myometrium
21
Q

Summarise what the stimulation physiological stage of labour is:

A

A release from inhibitory effect of pregnancy on myometrium “the breaks are off”

22
Q

Describe the physiological stimulation phase of labour

A
  • Mature fetus, timing right.
  • Pelvic ligaments softened
  • Uterus excitable and contractions coordinated.
  • Cervix soft and easily dialted
  • Membranes may rupture (more PGs and possible mechanical benefits)

PROSTAGLANDINS FACILITATE THIS

23
Q

What must happen for activation to become stimulation?

A

A positive feedback cascade i.e prostaglandins

24
Q

What facilitates the stimulation stage of labour?

A

Prostaglandins

25
Q

Describe the ripe cervix:

A
  • Collagen degrades
  • Increased spacing between fibres
  • Wavy fibres, allow immune cell infiltration
  • Glands proliferate
26
Q

Prostaglandins are important in labour, what is the implication of this from a generic viewpoint? What bigger picture are they a part of?

A

Inflammation is important in labour

27
Q

What role do the membranes play in labour?

A
  • Retain strength i.e collagen
  • Site of PG production
  • MMPs degrade collagen and weaken - PGs, Inflammation, stretch, shear force, increase production

I.e rupturing membranes increase PG production

28
Q

What triggers the positive feedback cascade that leads to the stimulation phase?

A

Unsure, but in essence procontraction things outweight anti-contraction signals.

29
Q

How might time of day influence labour?

A

Melatonin (spike in night pregnancies)

30
Q

How can fetal stress influence labour?

A

Fetal stress -> ACTH -> cortisol -> Dec. placental;
(progesterone) Increases placental (estrogen, prostaglandins) -> this leads to contraction and retractions of myocytes -> stretch on cervix / lower uterus

+ive feedback to release oxytoinin = Inc contractions and retractions of myocytes

31
Q

insert station dilation slide

A

39

32
Q

What is involution?

A
  • Placental separation
  • Cleave through the decidua basalis
  • Contractions to prevent postpartum haemorrhage
  • Increased uterine sensitivity to oxytonin

Later ‘involution’ returns woman to non-pregnant state

33
Q

How can one help induce labour?

A
  • Progesterone antagonists
  • Prostaglandins
  • > might be caused by artificial ruptured membranes, stretch and sweep or giving PGE2
34
Q

How can a stalled labour be helped?

A

Nipple stimulation
Support person
Amniotomy
Syntocinon

35
Q

How can post partum haemorrhage be prevented?

A
  • Oxytonin
  • Prostaglandin
  • Carboprost
36
Q

How can pre-term labour be prevented?

A

Vaginal progesterone
Cervical cerclage (stitches)
Treating infection

37
Q

How can contractions be slowed?

A

Block Ca channels
Beta agonists i.e salbutimol
Block oxytonin receptors
Block PG synthesis i.e indomethacin

38
Q

What is the key hormone putting breaks on myometrium?

A

Progesterone

39
Q

How is activation acheived?

A

Activation/priming involves upregulation of gap junctions and CAPS (oestrogen/oxytonin receptors)

40
Q

How does stimulation occur?

A

With removal of factors that promote quiescence

- Progesterone withdrawal, inflammation, fetal signals, stretch

41
Q

What is the stimulation cascade characterised by?

A
  • Postive feedback loop, resulting in sychronous contractions
  • Changes of the composition of the cervix mean that it dilates as the fetal head descends
42
Q

Insert diagram of shunting

A

Slide 48

MBCHB3: Reproduction, Development and Ageing (24 decks)

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