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25 Cards in this Set

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What are the three theories regarding the physiologic mechanims for the onset of labor at term?
1. Progesterone Withdrawal Theory
2. Fetal-Maternal Communication
3. Oxytocin Induction Theory
Describe the Progesterone Withdrawal Theory.
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.
Is human parturition assoc w/ significant changes in levels of major steroid hormones or in estrogen:progestin ratio?
No, it's not associated with these changes.
What is the Fetal-Maternal Communication Theory?
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.
Do fetal glucocorticoids initiate the changes described by the Fetal-Maternal Communication theory?
No, the glucocorticoid effects in that theory describe observations in animals, not humans. However, glucocorticoids my be prermissive in the initation of human labor.
What is the Oxytocin Induction Theory?
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.
Which prostaglandins are synthesized in the endometrium and myometrium and what do they do?
PGE2 and PF2-alpha cause contractions of the uterus.
What is the role of PGE2 in labor?
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.
What is the fuctional unit for unterine activity?
The smooth muscle cell and surrounding connective tissue.
How is the action potential communicated b/w smooth muscle cells in the uterus?
By means of gap junctions.
Compare the number of gap junctions in the non-pregnant uterus w/ that of the pregnant uterus.
Few gap junctions exist in the non-pregnant uterus. They become larger and more numerous close to term.
What favors the increase in gap junction formation? What inhibits it?
The increase in estrogen:progestin ratio near term inc gap jnxn number. Prostaglandin also stimulates gap jnxn formation. Indomethacin inhibits it.
What is the first stage of labor?
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.
What is the Latent Phase of the first stage of labor?
It begins w/ the onset of regular uterine contractions to the beginning of the active phase.
What is the Active Phase of the first stage of labor?
It begins from the time the rate of cervical dilation begins to change rapidly to full dilation.
What is the second stage of labor?
It is the time from full dilation of the cervix to delivery of the infant. Maternal plasma oxytocin levels inc during this stage.
What is the third stage of labor?
It is from delivery of the infant to delivery of the placenta.
What are the seven cardinal movements of labor?
1. Engagement
2. Descent
3. Flexion
4. Internal Rotation
5. Extension
6. External Rotation
7. Expulsion
Describe the "Engagement" cardinal movement.
It is the first movement and may occur slowly over the last few weeks of pregnancy or after labor begins.
Describe the "Descent" cardinal movement.
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
Describe the "Flexion" cardinal movement.
Resistence by pelvic structures cause head to flex, decreasing fetal head diameter presenting to the pelvis.
Describe the "Internal Rotation" cardinal movement.
This is the positioning of the AP diameter of the head in position with the AP diameter of the pelvic outlet.
Describe the "Extension" cardinal movement.
The fetal head now starts to extend due to the new pelvic resistances it is meeting.
Describe the "External Rotation" cardinal movement.
The shoulders are in the AP diameter of the pelvis, i.e., one shoulder is anterior behind symphysis and the other is posterior.
Describe the "Expulsion" cardinal movement.
Once the anterior shoulder drops below the symphysis and the posterior negotiates the perineum, the body is quickly extruded.