normal and abnormal partruition Flashcards
Labor
Clinical definition- Cervical dilation, effacement, consistency, position and fetal head decend lead to birth
Achieved by uterine contractions occuring in a regular pattern
Uterine changes
The uterus undergoes tremendous change during pregnancy to allow for labor
Size increases, Cellular connectivity
Uterine increases in size from 7- grams to 1200 grams, significant increase in uterine blood supply (17% of CO by birth, vs 2% in non gravid, brain receives 15%), myometrial cell proliferation, myometrial cell hypertrophy
Gap juntions increase during pregnancy, this is key to labor contraction generation
Uterine contraction mechanism
Myometrial cells-
Contract spontaneously, are smooth muscle cells, contract due to actin and myosin myofilament interaction
An independent myometrial action potential, increase in intracellular calcium, Calcium binds calmodulin, myosin light chain kinase is activated
Myosin is phosphorylated (ATP is hydrolyzed), Myosin undergoes structural change, myosin forms a crossbridge with actin leading to contraction
Myometrial cells need to contract in synchrony to generate a uterine contraction- gap junctions between myometrial cells allow for action potentials to spend leading to cells to contract in synchrony
Timing of labor, why doesnt laboroccur throughout pregnancy- whats the mechanism that times labor for around 40 weeks
Labor phenotype- transition from the quiescence phase to labor phase involves a shift from progesterone dominance to estrogen dominance
Progesterone (inhibits intracellular calcium entry, inhibits release from sarcoplasmic reticulum, membrane hyperpolarize via potassium channels, inhibits expression of contraction associated protein genes, levels are constant before and during labor, tissue level may vary
Estrogen- increases gap junctions between myometrial cells allowing for contraction synchrony between cells, increasess oxytocin receptor and prostaglandin receptor expression in myometrium
Uterine stretch and estrogen upregulate contraction associated proteins in the myometrium
initiate excitation, increase frequency and amplitude of contractions
Gap junction protein connexin 43, oxytocin receptor, CRH receptor, COX 2 enzyme
Oxytocin
GPCR activates phospholipase C, stimulates Release of calcium from intracellular stores, myosin light chain kinase activation
Oxytocin synthesized by hypothalamus, stored in the posterior pituitary, increases prostaglandin and estrogen level
what is the trigger for labor
fetal adrenal gland, and the fetal HPA axis
Stages of labor
Regular contractions leading to cervial dilation over time
1st stage- latent phase- contraction with slow cervical dilation, active phase- contractions with fast cervical dilation
2nd stage- complete dilation until delivery of fetus
3rd stage- post delivery of fetus to delivery of placenta
4th stage- one hour after delivery of placenta, constant myometrial contraction that limits blood loss
Pre term labor
Definition- delivery between 20 weeks gestation and 37 Weeks gestation, contraction mechanism is the same
Pharmacology of preterm labor
Magnesium, Beta 2 agonists, CCB, Prostaglandin synthesis
Progesterone is preventative but does not stop preterm labor for past history and short cervic
causes of preterm labor
Uterine distention (CAP expression, CRH and estrogen increase, oxytocin release, uterine activation)
Infection (toxins produced by bacteria stimulate cytokine production leading to prostaglandin release)
Maternal fetal stress (premature rise in cortisol and estrogen can induce labor, phenotype and stimulate fetal adrenal c19 hormones
Preterm premature rupture of membranes- apoptosis of cellular compartment of fetal membrane matrix metalloproteinases play a role
Post partum hemorrhage
hemorrhage is the leading cause of international maternal mortiality, in the US thromboembolism is the leading cause thanks to standardize delivery practice
Post partum hemorrhage is best defined as bleeding leading to symptoms of hypovolemia (>500ml blood loss after vaginal or >1L after C section
Atony describes uterine relaxation during the 4th stage leading to excessive blood loss, pharmacologic treatment with oxytocin, prostaglandins, ergot alkaloid
