NM 704 Exam 1: Questions With Expert-Level Solutions
Explore the cascade of events believed to cause the initiation of labor. You do
not need to memorize Right Ans - There are placental, fetal and maternal
components. You should be able to give a couple of examples of each. All the
components are inter-related and there are many feedback loops.
Explore the cascade of events believed to cause the initiation of labor. You do
not need to memorize: Placenta Right Ans - declining progesterone and NO
leads to increased production of corticotropin releasing hormone (CRH) by
the placenta, CRH influences transition from progesterone to estrogen
dominance.
Explore the cascade of events believed to cause the initiation of labor. You do
not need to memorize: Fetal Right Ans - placental CRH goes to fetus,
stimulates fetal HPA -> cortisol production -> maturation of fetal lngs.
Triggers increased surfactant and phospholipid production ->induces uterine
ctx mediated in part by stimulation of prostaglandin synthesis in intrauterine
tissues. CRH stimulates fetal production of DHEA-S, which is a substrate of
estrogen.
Explore the cascade of events believed to cause the initiation of labor. You do
not need to memorize: Maternal Right Ans - Maternal: change from
progesterone dominance in quiescence to estrogen-stimulated uterotropin
activation. Pro-inflammatory substances (such as cytokines and leukocytes)
trigger responses in the uterus that increase prostaglandin production,
enhance ctx, and degrade extracellular matrix proteins to facilitate dilation.
Anatomic and physiologic changes of the cervix: Ripening Right Ans -
primary cause is collagen rearrangement. Modulated by inflammatory and
hormonal influences accompanied by increase in water content. Triggered by
increase in inflammation, oxytocin, and prostaglandin activity. Traction on the
cervix from uterine contractions may contribute prior to onset of labor.
Anatomic and physiologic changes of cervix: Effacement Right Ans -
lengthening of the muscle fibers at the internal os, which stretch the
endocervix upward into the lower uterine segment.
,Anatomic and physiologic changes of cervix: Dilation Right Ans - Cervical
os widens. Force of contraction plus hydrostatic action of amniotic fluid or
pressure from presenting fetal part promotes dilation on the softened/low
resistance cervix
Significance of Progesterone in the onset of labor Right Ans - inhibits
contractions. therefore decreases before labor
Significance of Estrogen in the onset of labor Right Ans - Uterotropin.
Causes uterine myometrial cells to express receptors for prostaglandins and
oxytocin and develop gap junctions.
Significance of Prostaglandins in the onset of labor Right Ans - Uterotropin,
uterotonin. Facilitate contractions, increase myometrial sensitivity to
oxytocin, and stimulates formation of gap junctions.
Significance of Oxytocin in the onset of labor Right Ans - Uterotonin.
Released in pulsatile fashion, peaks with fetal ejection reflex.
Significance of Oxytocin receptors in the onset of labor Right Ans - Binding
of oxytocin to receptors in the myometrium stimulates smooth muscle
contractions. Prostaglandin production in decidua stimulated by binding of
oxytocin receptors.
Significance of Gap Junctions in the onset of labor Right Ans -
transmembrane proteins that create a line of communication between two
adjacent myocytes. Action potentials that initiate contractions travel through
gap junctions to create a synchronized contraction
Describe the myometrium Right Ans - - Bundles of smooth muscle fibers.
Three distinct patterns.
- Inner layer: fibers run in a circular pattern that spirals in a perpendicular
orientation to the long axis of the uterus.
- Middle layer: fibers are interlaced and form figure-eight patterns running
diagonally along the long axis of the uterus.
- Outerlayer- arrangement of fibers in both longitudinal and spiral patterns
- Layers become more differentiated in pregnancy w/ hypertrophy and
myometrial cells. Fundus contains primarily muscle fibers, whereas only
10_15% of tissue mass in the cervix is comprised of muscle fibers.
, Myometrium Right Ans - ● The smooth muscle (myometrium) in the uterus
is anatomically different from other types of smooth muscle. Four layers each
of which produces a distinct response to substances that promote or inhibit
contractions
● Uterine muscle is thickest in fundus (greatest contractile strength) → active
segment
○ Muscle bundles in fundus progressively shorten with each contraction,
causing the upper portion of the uterus to thicken and gradually becomes a
smaller cavity→ promotes fetal descent toward more passive lower uterine
segment
● Uterine muscles become thinner toward the lower segment in the isthmus;
this thinner lower uterine segment form the muscular tube through which the
fetus passes
○ The lower uterine segment muscle bundles become longer in response to
contractions in the fundus, creating a distensible structure that is able to
accommodate the fetus, promotes fetal descent
● Physiological retraction ring→ line of demarcation between the active and
passive segment
○ When labor is obstructed the active segment becomes so much thicker and
shorter that one can sometimes see the line between the two uterine
segments → pathologic retraction ring or Bandl's ring
Myometrium activation vs stimulation Right Ans - Activation phase:
increased myometrial excitability and responsiveness to substances that
stimulate ctx. d/t estrogen influence, cells express receptors for prostaglandin
and oxytocin and develop gab junctions.
Triple Descending gradient: Right Ans - Contractions 1. start at the fundus
2. last longer in the fundus 3. progress from fundus to isthmus.
Muscle bundles in the fundus shorten w/ contractions, upper portion of
uterus thickens. Reduced fundal capacity promotes descent of the fetus.
Lower segment muscles become longer and more flexible and accommodate
the fetus.
Describe first 3 phases of parturition: Phase 0 Right Ans - Quiescence:
inhibitors of uterine contractions include progesterone, prostacyclin, relaxin,
nitric oxide, and other hormones
Explore the cascade of events believed to cause the initiation of labor. You do
not need to memorize Right Ans - There are placental, fetal and maternal
components. You should be able to give a couple of examples of each. All the
components are inter-related and there are many feedback loops.
Explore the cascade of events believed to cause the initiation of labor. You do
not need to memorize: Placenta Right Ans - declining progesterone and NO
leads to increased production of corticotropin releasing hormone (CRH) by
the placenta, CRH influences transition from progesterone to estrogen
dominance.
Explore the cascade of events believed to cause the initiation of labor. You do
not need to memorize: Fetal Right Ans - placental CRH goes to fetus,
stimulates fetal HPA -> cortisol production -> maturation of fetal lngs.
Triggers increased surfactant and phospholipid production ->induces uterine
ctx mediated in part by stimulation of prostaglandin synthesis in intrauterine
tissues. CRH stimulates fetal production of DHEA-S, which is a substrate of
estrogen.
Explore the cascade of events believed to cause the initiation of labor. You do
not need to memorize: Maternal Right Ans - Maternal: change from
progesterone dominance in quiescence to estrogen-stimulated uterotropin
activation. Pro-inflammatory substances (such as cytokines and leukocytes)
trigger responses in the uterus that increase prostaglandin production,
enhance ctx, and degrade extracellular matrix proteins to facilitate dilation.
Anatomic and physiologic changes of the cervix: Ripening Right Ans -
primary cause is collagen rearrangement. Modulated by inflammatory and
hormonal influences accompanied by increase in water content. Triggered by
increase in inflammation, oxytocin, and prostaglandin activity. Traction on the
cervix from uterine contractions may contribute prior to onset of labor.
Anatomic and physiologic changes of cervix: Effacement Right Ans -
lengthening of the muscle fibers at the internal os, which stretch the
endocervix upward into the lower uterine segment.
,Anatomic and physiologic changes of cervix: Dilation Right Ans - Cervical
os widens. Force of contraction plus hydrostatic action of amniotic fluid or
pressure from presenting fetal part promotes dilation on the softened/low
resistance cervix
Significance of Progesterone in the onset of labor Right Ans - inhibits
contractions. therefore decreases before labor
Significance of Estrogen in the onset of labor Right Ans - Uterotropin.
Causes uterine myometrial cells to express receptors for prostaglandins and
oxytocin and develop gap junctions.
Significance of Prostaglandins in the onset of labor Right Ans - Uterotropin,
uterotonin. Facilitate contractions, increase myometrial sensitivity to
oxytocin, and stimulates formation of gap junctions.
Significance of Oxytocin in the onset of labor Right Ans - Uterotonin.
Released in pulsatile fashion, peaks with fetal ejection reflex.
Significance of Oxytocin receptors in the onset of labor Right Ans - Binding
of oxytocin to receptors in the myometrium stimulates smooth muscle
contractions. Prostaglandin production in decidua stimulated by binding of
oxytocin receptors.
Significance of Gap Junctions in the onset of labor Right Ans -
transmembrane proteins that create a line of communication between two
adjacent myocytes. Action potentials that initiate contractions travel through
gap junctions to create a synchronized contraction
Describe the myometrium Right Ans - - Bundles of smooth muscle fibers.
Three distinct patterns.
- Inner layer: fibers run in a circular pattern that spirals in a perpendicular
orientation to the long axis of the uterus.
- Middle layer: fibers are interlaced and form figure-eight patterns running
diagonally along the long axis of the uterus.
- Outerlayer- arrangement of fibers in both longitudinal and spiral patterns
- Layers become more differentiated in pregnancy w/ hypertrophy and
myometrial cells. Fundus contains primarily muscle fibers, whereas only
10_15% of tissue mass in the cervix is comprised of muscle fibers.
, Myometrium Right Ans - ● The smooth muscle (myometrium) in the uterus
is anatomically different from other types of smooth muscle. Four layers each
of which produces a distinct response to substances that promote or inhibit
contractions
● Uterine muscle is thickest in fundus (greatest contractile strength) → active
segment
○ Muscle bundles in fundus progressively shorten with each contraction,
causing the upper portion of the uterus to thicken and gradually becomes a
smaller cavity→ promotes fetal descent toward more passive lower uterine
segment
● Uterine muscles become thinner toward the lower segment in the isthmus;
this thinner lower uterine segment form the muscular tube through which the
fetus passes
○ The lower uterine segment muscle bundles become longer in response to
contractions in the fundus, creating a distensible structure that is able to
accommodate the fetus, promotes fetal descent
● Physiological retraction ring→ line of demarcation between the active and
passive segment
○ When labor is obstructed the active segment becomes so much thicker and
shorter that one can sometimes see the line between the two uterine
segments → pathologic retraction ring or Bandl's ring
Myometrium activation vs stimulation Right Ans - Activation phase:
increased myometrial excitability and responsiveness to substances that
stimulate ctx. d/t estrogen influence, cells express receptors for prostaglandin
and oxytocin and develop gab junctions.
Triple Descending gradient: Right Ans - Contractions 1. start at the fundus
2. last longer in the fundus 3. progress from fundus to isthmus.
Muscle bundles in the fundus shorten w/ contractions, upper portion of
uterus thickens. Reduced fundal capacity promotes descent of the fetus.
Lower segment muscles become longer and more flexible and accommodate
the fetus.
Describe first 3 phases of parturition: Phase 0 Right Ans - Quiescence:
inhibitors of uterine contractions include progesterone, prostacyclin, relaxin,
nitric oxide, and other hormones
