Causes of onset of labor (4)
prostaglandins: the major sites of synthesis of prostaglandins are placenta,fetal membranes,decidual cells and myometrium. Synthesis is trigged by ---rise in estrogen level, altered estrogen-progesterone balance, mechanical stretching in late pregnancy, increase in oxytocin receptors specially in the decidua vera, infection, separation or rupture of the membranes.
Oxytocin:it is probable that myometrial contraction is more dependent on its own readiness to respond to oxytocin. oxytocin level reaches the maximum at the monent of the birth.