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8 Cards in this Set
- Front
- Back
3 theories for physiological mechanism for onset of labor at term (Obj 1)
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1. Progesterone withdrawal
(evidence is elusive: human parturition NOT assoc w/significant changes in levels of major steroid hormones or est:progest ratio) 2. Fetal-Maternal Communication: Animal Studies (NOT HUMANS)- fetal hypo stimulates fetal pit to incr ACTH ==>incr cortisol ==>incr est:progest ratio ==>labor 3. Oxytocin: **most supported theory in humans -inhibiting oxytocin can prevent labor -increased oxytocin lvels during labor (although oxytocin does not incr before labor) -uterine responsiveness to oxytocin incr dur pregnancy and is maximum at term |
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role of prostaglandins in labor
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*PGE2 and PF2 are synthesized in the endometrium/myometrium and cause uterine contractions
-giving prostaglandins at any point in pregnancy induces labor/abortion -fetal lung produces more and more prostaglandins as it matures==>thus might be a signal to mother that ready to be born |
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Mechanism for Uterine Contractions at the Cellular Level
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A. Smooth Muscle Contraction
-Ca activates contraction -intermediate filaments (100A) link myosin (150A) and actin (60A) ==>organized yet highly flexible mechanical unit ==>allows uterus to assume any shape necessary for contraction, regardless of fetal size or position B. Gap Jxns -this is how AP for contraction travels b/w cells -incr # gap jxns in pregnancy vs. non-preg -PG's stim production of gap jxns, indomethacin inhibits -incr est:progest ==>incr gap jxns C. Coordination of Contractions -reduced ability of SR to uptake Ca2+ causes higher intracellular Ca2+==>contract -PG, oxytocin, & ACh reduce Ca uptake==>contraction -progest & cAMP promote Ca uptake -near term, incr est:progest ratio ==> -incr # oxytocin receptors |
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what is important factor in the initation of uterine contractions?
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incr est:progest ratio==>
1. incr est receptors==> -incr oxytocin receptors -incr PG syn -incr gap jxns -incr intracell Ca decr progest==> -destabilize uterine and membrane lysosomes==>free enzymes that trigger PG production and active cervical collagenase |
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diff b/w nulliparas vs. multiparas women in preg
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for last 3 days of preg, mean cervical dilation is larger in multiparas (2.2 cm) than nulliparous (1.8 cm)
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Stages of Labor (Obj 3)
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Stage 1:
Onset of Labor==>Full Dilation of Cervix -starts when contractions become vigorousenough to cause effacement (shortening) and dilation of cervix -ends when cervix is dilated enough (10 cm) to allow passage of fetal head -PG increse during this phse (but not before) -NO increase in oxytocin *2 phases: -Latent Phase: onset of contractions-->start of active phase -Active Phase: when cervix begins to rapidly dilate (3-4 cm) til full dilation (10 cm) Stage 2: Full Dilation of Cervix==>Delivery of Baby -incr oxytocin Stage 3: Delivery of Baby==>Delivery of Placenta -very important to deliver the placenta. In the past, failure to deliver placenta caused infxn. |
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Cardinal Mvmts of Labor (Obj 4) & positon of fetal head (Obj 5)
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1. Engagement
-passage of biparietal diameter (greatest transverse diameter of flexed fetus head) thru pelvic inlet 2. Descent -baby must descend to be born **descent beyond engagement may not occur in nulliparas, but may begin with engagement in multiparas 3. Flexion -head flexes d/t resistence by pelvic structure 4. Internal Rotation -head rotates into Ant-post diameter of pelvic inlet 5. Extension -head must extend 6. External Rotation -sholders rotate to ant-post position 7. Expulsion -first ant shoulder, then post shoulder |
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diff in labor b/w nulliparas vs. multiparas
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-last 3 days of preg, cervix dilated more in multiparas (2.2 cm) vs. nulliparas (1.8 cm)
-descent beyond engagement may not occur in nulliparas, but may begin with engagement in multiparas |