LC Exam 2: Parturition Flashcards
Pressure changes during labor and blood flow
Uterine smooth muscle at rest: 25mmHg
Contraction: up to 120mmHg
Pain is ischemic from spiral arteries (placenta is transiently hypoxic, but Wharton’s jelly maintained baby perfusion)
Structure of the cervix and dilation
Mostly collagen 1 and 3
Dilates with contractions, proteases degrade
Internal portion is the part that needs to be dilated (melts away)
Dilation easier in multi-pardous women
Cervical insufficiency
Painless delivery early - miscarrage
Disorganized cervical collagen, can’t hold baby
Stages of labor
1: Contractions to obtain dilation of cervix
2: Complete dilation to delivery of fetus
3: Delivery of fetus to delivery of placenta
4: First 6 hours post
Myometrial phases of labor
0: Quiescence
1: Activation
2: Stimulation (marks 1st stage of labor)
3: Involution (4th stage of labor)
Hormonal keys of myometrial phases
0: Progesterone
1: Estrogen, progesterone (receptor switching), uterine stretch, fetal signal (CRH)
2: Prostaglandins, oxytocin, CRH
3: Oxytocin, inflammatory cells
Uterus growth during pregnancy
Lots of growth Increased oxytocin receptor density Becomes synctyal electrical system (synchonicity): Increased connexon density/gap jxns Mechanotransmission as well
Myometrial inhibtors
Progesterone (blocks myosin light chain, PG inhibitor)
CRH (quiescence in early pregnancy)
Myometrial stimulators
CRH (later)
Oxytocin (receptor increase in labor)
Prostoglandins (receptor increase in labor)
Ca2+ (channel increase in labor)
Oxytocin
Stimulates contraction
Increases Ca2+
Activates myosin LC kinase
Increases PG
Prostaglandins
Source: myometrium, placenta
Increases Ca2+
Weakens amnion and chorion
Membrane PG DH decreases during labor, which increases PG levels
CRH
Switches fxn
Early: quiesence, blocks myosin LC kinase (cAMP, NO)
Late: contraction, activates PKC
Receptor switching
CRH levels increase late (fetus production)
CRHBG goes down at end of preg
Preterm labor treatments
Can only delay up to 48 hours, give course of steroids Calcium antag Oxytocin antag PG inhibitors NO donors Beta-mimetics Mg2+
Ligand - receptor - action:
Prostaglandin
Oxytocin
Epi
PGE2/PGE1 - EP1: Gq - myometrial contraction
PGE2/PGE1 - EP2-4: Gs - cervical ripening/dilation
PGF2a - FP: Gq - myometrial contaction
Oxytocin - OXT: Gq - myometrial contaction
Epi - ß2: Gs - myometrial RELAXATION
Stages and hormones
Stage 1: cervical dilation = prostaglandin
Stage 2: uterine contaction = PG/oxytocin via L-type Ca and ß2 for relaxation
Stage 3: placental delivery = oxytocin hemostasis
Misoprostol
Dinoprostone
M: PGE1 - EP1R in myometrium (better systemically)
D: PGE2 - EP1R in myometrium (lots of AR systemically, can do locally for cervical effect as well)
Note: EP2-4 in cervix
Pitocin
Oxytocin analoge
Milk letdown
Labor induction (no effect on cervix, needs to be dilated)
Useful for postpartum bleeding
Tocolytic agent use and agents
Delay pregnancy up to 48 hours
Betamethasone for lung development
Can’t use cortisol -> placenta inactivates
Terbutaline, indomethacin, ethanol, Mg, Nifedipine
Terbutaline
ß2-agonist
Suppresses contractions, not after 48-72 hours
No affect on PG - less effective is dilated and ruptured
Maternal side effects
Indomethacin
COX 1 and 2 blocker, inhibits PG’s
Used 24-32 weeks
PG -> maintain patent DA
Ethanol
Theoretical. Not used.
MgSO4
Older medication, not used unless anticonvulsant for pre-ecamplsia/ecamplisia
Compete with Ca2+
Nifedipine
Ca channel blocker
Used 32-34 weeks (can use 24-32 if CI to indo.)
Fewer side effects than Mg or ß-ag
17 a hydroxyprogeterone caporate
Progesterone metabolite
Prevent preterm labor
Given 1 week/IM at 16/20 wks pregnant until 36 wks
Hx of >/=1 previous spontaneous preterm birth
Mifepristone
Progesterone antagonist
Early termination
Followed 36-48 hours by prostaglandin to contract rest of contents
(Uterus insensitive to oxytocin until 20-36 weeks)
