by mtoom

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Name and describe the 4 phases of pregnancy?
  • Phase 0: Uterine quiescence 
  • Phase I: Uterine preparedness
    -Functional change in myometrium and cervix 
  • Phase II: Active labour
    -Progressive cervical dilation and fetal delivery 
  • Phase III: Uterine involution 
    -Fertility restored 
When is the initation of parturition?
Between Phase 0 and Phase 1
Describe the sheep model for parturition
  • ↑ACTH
  • ↑Cortisol from adrenals
  • ↑Androgens from placenta
  • ↑Estradiol in mother
  • ↓Progesterone in mother
Alteration in estrogen/progesterone balance leads to initiation of labour in sheep
What do uterotropins do? *
Set the stage for contractions and cervical change
Name the uterotropins. * (4)
  • Estrogen
  • Relaxin
  • Ca++-dependent phospholipases
  • Arachidonic acid → prostaglandins
What hormone counteracts the uterotropins to maintain uterine quiescence? *
What do uterotonins do? *
Directly involved in the contraction of myometrial smooth muscle cells
  • ↑intracellular calcium in myometrium
Name the uterotropins. * (3)
  • Oxytocin
  • Prostaglandins (especially PGF2α)
  • Endothelin-1
Answer these questions (with regard to humans):
  • Do serum progesterone levels fall?
  • Do serum estradiol levels rise?
  • Does administration of progesterone reliably prevent preterm labour?
  • Does administration of estrogen reliably induce labour?
  • Do levels of prostaglandins, arachidonic acid, relaxin, phospholipases, cortisol and oxytocin rise before active labour?
Answer is NO to all questions
What exactly initiates parturition in humans? *
What are prostaglandins?
Biologically active lipids synthesized at or near their site of action
  • Interface of the amnion/chorion and myometrium 
  • What induces prostaglandin production?
  • Which hormone inhibits PG production
  • Inflammatory response induces prostaglandin production
  • Progesterone inhibits prostaglandin production
What is the main effect of PGE2? * (2)

Cervical effacement
  • Breakdown of the rigid structure of collagen fibers (unwinds them)
  • Softens the ECM (increased hyaluronic acid, decreased GAGs)

Highest levels in amniotic fluid just below presenting part (i.e. "forewaters")
What is the main effect of PGF2α? *
Increases intracellular Ca++
What mechanism causes production of PGF2α?
  • Thinning of lower uterine segment during active labour
  • Inflammatory response in decidua
  • Arachidonic acid released and converted into PGF2α
  • Process is also stimulated by oxytocin
  • Where is oxytocin produced?
  • Where is oxytocin secreted from?
  • When is oxytocin secreted?
  • Where are oxytocin receptors

  • Produced in hypothalamus
  • Secreted from posterior pituitary
  • Receptors present on myometrium
What does oxytocin do? *
Increases intracellular Ca++
  • Activates Phospholipase C intra cellular pathway
  • Leads to activation of IP3 and DAG
  • Leads to release of Ca++ from sarcoplasmic reticulum
  • Releases Ca++
What does Ca++ do inside the cell that promotes myometrial contractions?
  • Intracellular Ca++ and calmodulin activate MLCK kinase which phorphorylates myosin light chains
  • Phosphorylated myosin light chains binds with actin to form P-actomyosin
Physiologically, what happens during myometrial relaxation? (4)
  • Decreased intracellular Ca++
  • Sequestration of Ca++ into sarcoplasmic reticulum
  • Dephosphorylation of myosin light chain kinase
  • Inactivation of MLCK (by cAMP-dependent phosphorylation)

Labour is a continuous process of contractions alternating with relaxation
In myometrium, describe:
  • Muscle filaments
  • Gap junctions 
  • Muscle filaments: Thick and thin filaments arranged into long, random bundles to allow muscle shortening in any direction and maximize the shortening
  • Gap junctions:
    -Transcellular membrane channels
    -Allow ion exchange
    -Propagate electric signal
    -Increase in number close to parturition (increased by estradiol, decreased by progesterone) 
What is meant by cervical ripening?
When the cervix becomes soft and distensible
Which mediators cause cervical ripening? * (4)
  • ↑Estradiol
  • ↑Arachidonic acid
  • ↑PGE2
  • ↓Progesterone
What mechanisms cause contractions and what mediators contribute to these mechanisms? * (2)
Contractions due to the interaction of actin and myosin filaments which are mediated in the following ways:
  • ↑Ca++
    -↑oxytocin, oxytocin receptors
  • Gap junctions
Explain the active segment and passive segment and what happens in labour?
  • Active segment: Thickens
  • Passive segment: Thins
  • Cervix: Dilates 
Acts to push out baby
Name the 4 aspects of the Leopold maneuvers
  • Lie
  • Presentation
  • Presenting part
  • Position
  • What is effacement?
  • What is cervical dilation
  • Cervical effacement: Thinning of cervix
  • Cervical dilation: Cervix opens up
What is the definition of labour?
Progressive cervical dilation, effacement, or both, resulting from regular uterine contractions every 5 minutes last 30-60 seconds
What is Phase II ?
Active labour
What are the 4 stages of Phase II?
  • 1st stage
    -Onset of involuntary painful regular contractions to full dilation
    -Latent & Active phase
  • 2nd stage
    -Full dilation to delivery of fetus
  • 3rd stage
    -Delivery of fetus to delivery of placenta
  • 4th stage
    -Delivery of placenta to stabilization of maternal condition 
Describe the latent phase of the first stage of Phase II (3)
  • Onset of regular painful contractions every 5 min lasting 30-60 sec
  • Cervix <3cm dilated
  • Extremely variable duration
Describe the active phase of the first stage of Phase II (4)
  • Regular painful contractions every 2-3 minutes lasting 45-60 sec
  • Cervix: 3-4cm to fully dilated (10cm)
  • Nulliparas: 1cm/hr
  • Multiparas: 1.2cm/hr
What happens in second stage of Phase II?
  • Describe the forces that push fetus out 
Full cervical dilation to delivery of fetus
The majority of pushing that gets the baby out is from what? *
Uterine contractions (which are only assisted by maternal pushing efforts)
Name the cardinal movements of delivery (7)
  • Engagement
  • Descent
  • Flexion
  • Internal rotation
  • Extension
  • External rotation
  • Expulsion
What is the purpose of cardinal movements of delivery?
Minimize fetal diameters as they pass through narrowest diameters of pelvis
What occurs in 3rd stage of Phase II?
Delivery of baby to delivery of placenta
  • 0-30 minutes
  • Blood clot forms
  • Placenta slides into lower uterus
  • Delivery occurs by maternal pushing and gentle traction on cord 
What are classic signs of placental separation? (4)
  • Gush of blood
  • Lengthening of cord
  • Fundus rises up
  • Uterus becomes firm and globular
What is meant by "active management" in the 3rd stage of Phase II?
  • Why is it good? 

Active management reduces risk of postpartum hemorrhage

Involves uterotonics, gentle cord traction and possible early cord clamping 
  • 1 L/min maternal blood flows into uterus at term
  • Uterus needs to contract down on all vessels in order to stop bleeding
What happens in the 4th stage of Phase II?
  • 1 to 1.5 hr after delivery of placenta
  • Bleeding slows
  • Utertus remains contracted
  • Maternal stabilization and bonding
  • 1st attempt at breastfeeding
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