Uterine contractions that lead to expulsion of the fetus to extra uterine environment Towards the end of pregnancy the uterus become progressively more excitable and develops strong rhythmic contractions that lead to expulsion of the fetus ID: 778839
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Slide1
Parturition
Definition
Uterine contractions that lead to expulsion of the fetus to
extra uterine
environment
Towards the end of pregnancy the uterus become progressively more excitable and develops strong rhythmic contractions that lead to expulsion of the fetus.
Slide2Parturition
Uterus is spontaneously active.
Spontaneous depolarization of pacemaker cells.
Gap junctions spread depolarization Exact trigger is unknownHormonal changesMechanical changes
Slide3Hormonal changes
Estrogen & Progesterone
Progesterone inhibit uterine contractility
Estrogen stimulate uterine contractilityFrom 7th month till term Progesterone secretion remain constantEstrogen secretion continuously increase Increase estrogen/progesterone ratio
Slide4Slide5Hormonal changes
Progesterone
▼ GAP junctions
▼ Oxytocin receptor▼prostaglandins.▲ resting membrane potential
Estrogen
▲ GAP junctions with onset of labour.
▲
Oxytocin
receptors.
▲ Prostaglandins
P
E
Slide6Hormonal changes
Oxytocin
Dramatic
▲of oxytocin receptors (200 folds) gradual transition from passive relaxed to active excitatory muscle (↑responsiveness).Increase in oxytocin secretion at laborOxytocin increase uterine contractions byDirectly on its receptorsIndirectly by stimulating prostaglandin production
Slide7Hormonal changes
Prostaglandins
Central role in initiation & progression of human labor
Locally produced (intrauterine)Oxytocin and cytokines stimulate its productionProstaglandin stimulate uterine contractions by:Direct effect: Through their own receptorsUpregulation of myometrial gap junctions
Indirect effect:
upregulation
of
oxytocin
receptors
Slide8Effect of fetal hormones on uterus
1-Fetal pituitary secrete oxytocin which might play a role in uterine excitation
2-fetal adrenal glands secrete cortisol
also can stimulate uterus
3- Fetal membrane secrete prostaglandins
Slide9Mechanical changes
Stretch of the uterine muscle
Increases contractility
Fetal movementsMultiple pregnancyStretch of the cervixIncreases contractility (reflex)Membrane sweeping & rupture (induction contraction)Fetal headPositive feedback mechanism
Slide10Positive feedback mechanism
Slide11Figure 16.19, step 1
Initiation of Labor
Baby moves
deeper into
mother’s birth
canal
Slide12Figure 16.19, step 2
Initiation of Labor
Pressoreceptors
in cervix of
uterus excited
Baby moves
deeper into
mother’s birth
canal
Slide13Figure 16.19, step 3
Initiation of Labor
Afferent
impulses to
hypothalamus
Pressoreceptors
in cervix of
uterus excited
Baby moves
deeper into
mother’s birth
canal
Slide14Figure 16.19, step 4
Initiation of Labor
Hypothalamus sends efferent
impulses to posterior pituitary,
where oxytocin is stored
Afferent
impulses to
hypothalamus
Pressoreceptors
in cervix of
uterus excited
Baby moves
deeper into
mother’s birth
canal
Slide15Figure 16.19, step 5
Initiation of Labor
Hypothalamus sends efferent
impulses to posterior pituitary,
where oxytocin is stored
Posterior pituitary releases
oxytocin to blood; oxytocin
targets mother’s uterine
muscle
Afferent
impulses to
hypothalamus
Pressoreceptors
in cervix of
uterus excited
Baby moves
deeper into
mother’s birth
canal
Slide16Figure 16.19, step 6
Initiation of Labor
Hypothalamus sends efferent
impulses to posterior pituitary,
where oxytocin is stored
Posterior pituitary releases
oxytocin to blood; oxytocin
targets mother’s uterine
muscle
Uterus responds
by contracting
more vigorously
Afferent
impulses to
hypothalamus
Pressoreceptors
in cervix of
uterus excited
Baby moves
deeper into
mother’s birth
canal
Positive feedback
mechanism continues
to cycle until interrupted
by birth of baby
Slide17Phases of parturition
Phase 0
From conception to beginning of labor;
uterus is relaxed (quiescent)Phase 1Activation: expression of contraction proteinsPhase 2Stimulation: stage 1& stage 2 of labor cervical dilatation & expulsion of fetusPhase 3 = stage 3 of laborDelivery of the placenta and uterine involution
Slide18Slide19Uterine Activity During Pregnancy
4/22/2018
19
Inhibitors
Progesterone
Prostacycline
Relaxin
Nitric Oxide
Parathyroid hormone-related peptide
CRH
HPL
Quiescence
Uterotonins
Prostaglandins
Oxytocin
Stimulation
Uterotrophins
Estrogen
Progesterone
Prostaglandins
CRH
Activation
Involution
Oxytocin
Thrombin
Involution
Slide20Phase 0:
quiescent uterus: associated with
Increased cAMP, due to progesterone,
relaxin
, prostacyclin,
PTH-related peptide, NO
Phases of parturition
Adapted from Smith, 2007
Slide21Phases of parturition
Phase 1 (activation)
Occurs in third trimester
Promote a switch from quiescent to active uterusIncrease excitability & responsiveness to stimulators by Increase expression of gap junctionsIncrease G protein-coupled receptorsOxytocin receptorsIncrease PGF receptors
Slide22Phases of parturition
Phase 1:
activation of uterus
upregulation
of contraction-associated proteins -- connexin-43 -- increase gap junctions
50X increase
myometrial
oxytocin receptors
uterus responsive to uterotonins
dilation and effacement of cervix, cervical softening due to rearrangement of collagen fibers,
Slide23Phases of parturition
Phase 2 (stimulation)
Occurs in last 2-3 gestational weeks Increase in synthesis of
Cytokines
Prostaglandins
Oxytocin
Includes 2 stages:
Stage 1
Stage 2
Slide24Phases of parturition
Phase 3 (uterine involution)
Pulsatile
release of oxytocinDelivery of the placenta Involution of the uterusOccurs in 4-5 weeks after deliveryLactation helps in complete involution
Slide25Braxton-Hicks contractions
-- irritability of uterine
muscle --- weak, slow contractions -- begins about 1 month before laborIn contrast: stronger contractions stretch cervix and
force baby
through birth canal
True labor has circadian
rhythm, peaks
between 12 midnight and 5 am.
“labor pains” --
due to ischemia of uterine muscle in early
stage, then stretch of cervix, perineum, vagina
Slide26Mechanics of Parturition
Contractions start at the fundus and spreads to the lower segment
The intensity of contractions is strong at the fundus but weak at the lower segment
In early stages 1 contraction/ 30 minuetsAs labor progress 1 contraction/ 1-3 minutesAbdominal wall muscles contractRhythmical contractions allows blood flow
Slide27Parturition:
Denotes the whole process
by which the baby is born.Labor: Strong uterine contractions, cervical dilatation, forcing the fetus through the birth canal
Labor and Parturition
Slide28Onset of labor
During pregnancy
Periodic episodes of weak and slow rhythmical uterine contractions (Braxton Hicks) 2
nd trimesterTowards end of pregnancyUterine contractions become progressively stronger & regularSuddenly uterine contractions become very strong leading to: cervical effacement and dilatation
Slide29Mechanisms of labor
Effacement
Dilatation
Three “P’s”PowersUterine activityPassagePassenger4/22/2018
29
Slide30Cervical effacement
Effacement is the process by which the cervix prepares for delivery. After the baby has engaged in the pelvis, it gradually drops closer to the cervix; the cervix gradually softens, shortens and becomes thinner. You may hear phrases like "ripens," or "cervical thinning" which refers to effacement.
Slide31Stages of labor
Stage 1:
Commences with the onset of labor and terminates when the cervix has reached full dilatation and membranes ruptured (lasts 8-24 hours).
Stage2:Stage of expulsion begins at full cervical dilatation and ends with expulsion of the fetus (lasts 1-30 minutes).stage 3: Begins with the delivery of the child and ends with the expulsion of the placenta.
Slide321
2
3
Stages of labor
Slide33Stages of Labor
Dilation
Uterine contractions begin and increase
Cervix softens and effaces (thins)Cervix becomes dilatedFull dilation is 10 cmThe amnion ruptures (“breaking the water”)Longest stage at 6–12 hours
Slide34Figure 16.20 (1 of 3)
Stages of Labor
Slide35Stages of Labor
Expulsion
Infant passes through the cervix and vagina
Can last as long as 2 hours, but typically is 50 minutes in the first birth and 20 minutes in subsequent birthsNormal delivery is head first (vertex position)Breech presentation is buttocks-first
Slide36Stages of Labor
Figure 16.20 (2 of 3)
Slide37Stages of Labor
Placental stage
Delivery of the placenta
Usually accomplished within 15 minutes after birth of infantAfterbirth—placenta and attached fetal membranes All placental fragments should be removed to avoid postpartum bleeding
Slide38Stages of Labor
Figure 16.20 (3 of 3)
Slide39New arrival