Parturition

The signals for parturition originate from the fully developed foetus and the placenta.
They induce mild uterine contractions called the foetal ejection reflex, which triggers release of oxytocin from the maternal pituitary.
Oxytocin is released in response to these signals; it is not their origin.

The signals for parturition originate from the fully developed foetus and the placenta and induce mild uterine contractions, called the foetal ejection reflex.
This triggers the release of oxytocin from the maternal pituitary.
Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulate further secretion of oxytocin.
This stimulatory reflex continues, giving stronger and stronger contractions, until the baby is expelled through the birth canal.
Hence parturition requires the release of oxytocin from the maternal pituitary.

Parturition is induced by a complex neuroendocrine mechanism.
The signals for parturition originate from the fully developed foetus and the placenta; they induce mild uterine contractions called the foetal ejection reflex.
This reflex triggers the release of oxytocin from the maternal pituitary.
Oxytocin acts on the uterine muscle and causes stronger contractions, which in turn stimulate further secretion of oxytocin, until the baby is expelled.
So oxytocin release is a result of the signals, not their origin.
Hence the signals originate from the placenta as well as the fully developed foetus.