Lecture 15 Flashcards by Tom Fresen

what is parturition

delivery
process of labour
conclusion of pregnancy
highly coordinated event

complex interactions between maternal and foetal tissues

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when does parturition occur?

37-42 weeks

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24 weeks delivery

limited viability

8% of births

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from 23 weeks onwards

survival output increases by 10% every 7 days

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neonatal death

respiratory distress syndrome

75%

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causes of preterm birth

lactrogenic 
spontaneous preterm labour (PTL) 
previous preterm birth
age extremes
low BMI 
periodontal disease 
drug abuse

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ethnicity and preterm labour

blacks - 18%

caucasians - 11%

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events before parturition

increase in relaxin
increase in progesterone
increase in PGI2

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relaxin before parturition

ligaments and connective tissue around pelvis and cervix loosen

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progesterone before parturition

prevents contraction of smooth muscle cells in uterus

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PGI2 before parturition

vasodilator to relax smooth muscles

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events in parturition

ripening and dilation of cervix 
myometrial contractions 
rupture of foetal membranes 
delivery of infant 
delivery of placenta

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1st stage of parturition

dilation of cervix - latent phase and active phase

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latent phase

1st stage of parturition

slow irregular contractions
cervix shortens
softens
dilates 3cm

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active phase

1st stage of parturition

regular painful contractions
4-10cm progressive dilation
membrane ruptures

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2nd stage of parturition

baby born 
4 hours born within reaching 10cm dilation 
cervix fully effaced and dilated 
head enters birth canal 
myometrial contractions

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how far apart are myometrial contractions

2-3 mins

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uterus in 2nd stage of parturition

uterus contracts up
baby pushed down
cervix pulls up then widens
baby comes out

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3rd stage of parturition

delivery of placenta
uterus contracts between deliveries
placenta detaches and delivered

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why does uterus contract between deliveries

prevent excessive bleeding from uterine arteries

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mechanisms of labour

ripening and dilation of cervix
myometrial contractions
prostaglandins
variety of actions induced

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ripening and dilation of cervix

inflammatory mediators

mechanical stimuli

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myometrial contractions

inflammatory mediators
hormones
cell-cell communication

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prostaglandins

pro-inflammatory mediators
lipid metabolites
produced locally at site of inflammation

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labour induced actions

constriction and dilation of smooth muscles alter vascular tone and permeability regulates calcium movement sensitises neurones to pain induces fever to fight infections

cervical changes

dilation induces contractions allows baby to push through positive feedback more relaxin hormone produced

ripening and softening of cervix

85% of cervix is connective tissue

inflammatory processes

leukocytes infiltrate cervix breakdown of collagen fibres by proteases (MMPs)

PGE2

key mediator of cervix ripening

cervical dilation

induced by myometrial contractions push baby head down onto cervix pressure on softening causes dilation

myometrial contractility by what hormone

oxytocin

where is oxytocin produced and released

hypothalamus | posterior pituitary gland

whats happens when uterus stretches

stretching signals vagus afferent transmits to brain releases oxytocin

how to check for myometrial contractility

tocograph

what hormone stimulates myometrial growth

estrogen

estrogen does what to smooth muscles

hyperplasia | hypertrophy

progesterone in myometrial contractility

key mediator of myometrial quiescence suppresses normal excitable behaviour of smooth muscles prevents contractions

how is the uterus prepared for contractions

progesterone is suppressed

CAPs myometrial contractility

contraction-associated proteins upregulation of CAPs

production of uterones

stimulate contraction oxytocin PGF2a

how is uterine smooth muscle contracted

depolarisation of smooth muscle cells 3Na+ in / 2K+ out increase in intracellular Ca2+ contraction

myosin-actin interactions

contract smooth muscle myosin filaments are activated myosin head domain binds to filament action ATP hydrolysis drives force to walk along filaments to induce contractions

myosin activation

changes phosphorylation state of myosin using phosphotases

myosin contraction

MLC-P

myosin relaxation

MLC

myosin light chain

smooth muscle cell contraction cascade

``` action potential Ca2+ influx Ca2+ binds to calmodulin activates MLC kinases MLC phophotases ```

oxytocin

increased pulsatile release during labour synthesised by uterus at term acts on oxytocin receptors on myometrial cells responsible for contractions

how does oxytocin stimulate contractions

augments excitability of myometrial cells increase frequency of of action potential increases frequency and amplitude of contractions

PGF2a

produced by decidua, foetal membranes and leukocytes infiltrating uterus

what does PGF2a stimulate

action potentials, ca2+ then contractions

cellular communications by what?

connexon/ connexin 43/ gap junctions

connexin bridge

1 connexin from 1 cell will bridge across extracellular space to another coordinates depolarisation across cells

when are connexons important?

during CAPs

triggers of parturition

hormones mechano-sensitisation (stretch_ inflammation

inflammation during parturition

leukocytes infiltrate cervix, decidua and myometrium

what does inflammation produce during parturition

PGs cytokines proteases activation of NF-kB

NF-kB

increases COX2 PGF2a receptor connexin 43 oxytocin receptor

foetal lungs release what during inflammation

SP-A

what does SP-A do?

activates TLR to activate NF-kB to trigger leukocytes release amniotic fluid triggers inflammation for birth

hormonal triggers for birth

removes suppressive effects on myometrium functional progesterone withdrawal altered balance of progesterone receptor subtypes

estrogen during birth

increases to lead up | increased ERalpha in myometrium

how does estrogen activate the myometrium

stimulates gap junctions increases oxytocin and oxytocin receptor production increase PG synthesis

foetal hormones stress axis

suppressed during pregnancy | before birth HPA matures

what is made by the adrenals

cortisol | DHEA

cortisol increases

COX2 PGF2a PGE2

what is DHEA for

substrate for estrogen production

what does placenta synthesise

CRH increases levels long term triggers HPA placental clock

labour

COX2 increases PGs decrease in progesterone increase in oxytocin increase in gap junctions

drugs to induce labour

syntocin | pictocin

Lecture 15 Flashcards

(70 cards)