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8 Cards in this Set

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3 theories for physiological mechanism for onset of labor at term (Obj 1)
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
role of prostaglandins in labor
*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
Mechanism for Uterine Contractions at the Cellular Level
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
what is important factor in the initation of uterine contractions?
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
diff b/w nulliparas vs. multiparas women in preg
for last 3 days of preg, mean cervical dilation is larger in multiparas (2.2 cm) than nulliparous (1.8 cm)
Stages of Labor (Obj 3)
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.
Cardinal Mvmts of Labor (Obj 4) & positon of fetal head (Obj 5)
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
diff in labor b/w nulliparas vs. multiparas
-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