What is parturition?
" It is likely that a "parturition cascade" exists at term which removes the mechanisms maintaining uterine quiescence and recruits factors promoting uterine activity" UptoDate ~ uterus must change from being resistant to contraction to one capable of contraction to deliver baby and placenta
Which phase of labour does uterine parturition occur at?
Between phase 0 and phase 1
Phase 0 is uterine quiescene, no contractility
Phase 1 is uterine preparendness, functinal changes in myometrium and cervix in preparation for active labour (Phase 2)
How does preparation for uterine contractility (parturition cycle 0 occur in humans?
uterotonins: directly involved in contraction of uterine smooth muscle cells.
increase in intracellular calcium in myometrium via oxytocin, prostaglandins (specifically PGF2alpha), endothelin-1 (vasoconstrictor released by vascular endothelial cells)
BUT: serum progesterone does not fall, serum estradiol does not rise so exactly what initiates partuition is not known
What is the difference between uterotropins and uterotonins?
Uterotropins (set the stage for contraction and cervical change)
- relaxin (made by corpus luteum (+ or - G), then by placenta, etc; helps regulate hemodynamic changes, like increases cardiac output, relaxes/softens pubic symphysis)
- arachidonic acid -> prostaglandins
Uterotonins (directly involved in contraction of uterus)
What are some uterotropins (set the stage for cervical change)?
relaxin - hormone produced by the corpus luteum of the ovary, the breast and, during pregnancy, also by the placenta, chorion, and decidua. peaks at 14 days ovulation, declined if non-pregnant. mediates hemodynamic changes in pregnancy, such as increased CO, increased renal blood flow, better arterial compliance, relaxes pelvic ligaments. in males increases sperm motility.
In males, relaxin enhances motility of sperm in semen
Ca++ dependent phospholipases
arachidonic acid -> prostaglandins
progesterone coutneracts these actions and maintains uterine quiescence (non-contractility)
What are some uterotonins in humans?
reminder: uterotonins: directly involved in contraction of myometrium (sm muscle) (need increase in intracellular calcium)
- prostaglandins,sp. PGF2alpha
- endothelin-1 (potent vasoconstrictor, produced by vascular endothelial cells)
What is the role of prostaglandins in labour? What are the two most important ones?
~ prostaglandins - bioactive lipids made from arachidonic acid at or near their site of actions (local); interface with amnion/chorion and myometrium
Two key prostaglandins in labour:
PGE2 - responsible for cervical effacement, highest level near forewaters (where baby's head is) - > designed to break down rigid collagen fibers of uterus -> cervix lowers (effaces) in preparation for labour
"E for ease the cervix"
PGF2 alpha - responsible for uterine contraction -> increases intracellular Ca++ in myometrial smooth muscle cells
"F for fetus forward = uterine contractions"
progesterone inhibits prostaglandin production by increasing prostaglandin dehydrogenase (NSAIDs could work too)
Outline the role of oxitocin in labour?
- precursor of oxytocin made in hypothalamus, released from posterior pituitary in active labour
- oxytocin receptors present in myometrium (increase near term and with estradiol, downregulated by progesterone)
- oxytocin activates phospholipases C -> influence on sarcoplasmic reticulum -> increase in intracellular Ca++ in myometrium of uterus -> contraction
Why is uterine relaxation important during labour?
uterine contraction = reduced blood flow to the fetus, healthy fetus can tolerate reduced blood flow of about 1 minute at a time
myometrial relaxation - simple decrease in intracellular Ca++ (smooth muscle)
labour is a continuous process of contractions and relaxations
Outline physiology of labour? (estradiol, prostaglandins, progesterone, etc)
How does myometrium contract?
What is Cervidil?
PGE2 analogue, aids in cervical effacement