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25 Cards in this Set
- Front
- Back
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What are the three theories regarding the physiologic mechanims for the onset of labor at term?
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1. Progesterone Withdrawal Theory
2. Fetal-Maternal Communication 3. Oxytocin Induction Theory |
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Describe the Progesterone Withdrawal Theory.
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The theory is based upon the observation that:
1. Progesterone production by corpus luteum is essential for continuation of pregnancy up to 7 weeks. If corpus luteum removed before then, progesterone must be given to prevent spontaneous abortion. 2. Progesterone Tx dec incidence of premature labor after surgery in in women w/ Hx of premature delivery. |
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Is human parturition assoc w/ significant changes in levels of major steroid hormones or in estrogen:progestin ratio?
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No, it's not associated with these changes.
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What is the Fetal-Maternal Communication Theory?
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In some animal species, the fetal hypothal stimulates fetal pituit to secrete ACTH, causing a surge of cortisol from fetal adrenal. The inc secreted glucocorticoids direct placental or luteal steroid synth to estrogens instead of progesterone, initiating labor.
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Do fetal glucocorticoids initiate the changes described by the Fetal-Maternal Communication theory?
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No, the glucocorticoid effects in that theory describe observations in animals, not humans. However, glucocorticoids my be prermissive in the initation of human labor.
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What is the Oxytocin Induction Theory?
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It says that the number of oxytocin receptors in the myometrium increases before the onset of labor. This allows labor at term to be induced w/ oxytocin in doses that result in plasma oxytocin levels in the physiologic range.
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Which prostaglandins are synthesized in the endometrium and myometrium and what do they do?
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PGE2 and PF2-alpha cause contractions of the uterus.
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What is the role of PGE2 in labor?
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In addition to causing contractions of the uterus, PGE2 also ripens the cervix by inducing changes in connective tissue. As the fetal lung matures, it is a source of inc amts of PG's.
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What is the fuctional unit for unterine activity?
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The smooth muscle cell and surrounding connective tissue.
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How is the action potential communicated b/w smooth muscle cells in the uterus?
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By means of gap junctions.
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Compare the number of gap junctions in the non-pregnant uterus w/ that of the pregnant uterus.
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Few gap junctions exist in the non-pregnant uterus. They become larger and more numerous close to term.
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What favors the increase in gap junction formation? What inhibits it?
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The increase in estrogen:progestin ratio near term inc gap jnxn number. Prostaglandin also stimulates gap jnxn formation. Indomethacin inhibits it.
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What is the first stage of labor?
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It starts at the onset of labor and lasts to full dilation of the cervix. There is no increase in Oxytocin during this stage. This stage has two phases: Latent Phase & Active Phase.
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What is the Latent Phase of the first stage of labor?
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It begins w/ the onset of regular uterine contractions to the beginning of the active phase.
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What is the Active Phase of the first stage of labor?
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It begins from the time the rate of cervical dilation begins to change rapidly to full dilation.
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What is the second stage of labor?
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It is the time from full dilation of the cervix to delivery of the infant. Maternal plasma oxytocin levels inc during this stage.
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What is the third stage of labor?
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It is from delivery of the infant to delivery of the placenta.
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What are the seven cardinal movements of labor?
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1. Engagement
2. Descent 3. Flexion 4. Internal Rotation 5. Extension 6. External Rotation 7. Expulsion |
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Describe the "Engagement" cardinal movement.
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It is the first movement and may occur slowly over the last few weeks of pregnancy or after labor begins.
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Describe the "Descent" cardinal movement.
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The fetus begins to descend through the pelvis. There are 4 forces that contribute to descent:
1. Pressure of amnniotic fluid 2. Direct pressure of contracting fundus 3. Valsalva maneuver pressure 4. Straightening & extension of fetal body |
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Describe the "Flexion" cardinal movement.
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Resistence by pelvic structures cause head to flex, decreasing fetal head diameter presenting to the pelvis.
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Describe the "Internal Rotation" cardinal movement.
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This is the positioning of the AP diameter of the head in position with the AP diameter of the pelvic outlet.
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Describe the "Extension" cardinal movement.
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The fetal head now starts to extend due to the new pelvic resistances it is meeting.
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Describe the "External Rotation" cardinal movement.
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The shoulders are in the AP diameter of the pelvis, i.e., one shoulder is anterior behind symphysis and the other is posterior.
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Describe the "Expulsion" cardinal movement.
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Once the anterior shoulder drops below the symphysis and the posterior negotiates the perineum, the body is quickly extruded.
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