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Signals from fully developed foetus and placenta ultimately lead to parturition which requires the release of
estrogen from placenta
oxytocin from maternal pituitary
oxytocin from foetal pituitary
relaxin from placenta.
Solution
(b) : Parturition is induced by a complex neuroendocrine mechanism. The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex. This triggers release of oxytocin from the maternal pituitary. Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates further secretion of oxytocin. The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contractions. This lead to expulsion of the baby out of the uterus through the birth canal.
