Q.Explain the neuroendocrine mechanism underlying parturition, including the role of the foetal ejection reflex and oxytocin.

[!TLDR]

The foetal ejection reflex is a positive-feedback loop -- foetal-head pressure and mild contractions trigger oxytocin, which strengthens contractions and increases cervical stretch, triggering yet more oxytocin -- that escalates until delivery. …

As the foetus reaches full term, mild, irregular uterine contractions increase, and pressure exerted by the foetus's head against the cervix generates sensory signals relayed to the mother's hypothalamus. These signals stimulate release of oxytocin from the posterior pituitary; oxytocin acts directly on the myometrium to make contractions stronger, and it also stimulates the placenta to release prostaglandins, which further intensify uterine contractility. Unlike most hormonal loops, which work by negative feedback, this is a positive-feedback loop: stronger contractions push the foetal head more firmly against the cervix, stretching it further, which generates even stronger sensory signals to the hypothalamus and triggers release of still more oxytocin, which again intensifies the contractions. This escalating cycle, the foetal ejection reflex, causes contractions to grow progressively stronger, longer and more frequent until they are powerful enough to fully dilate the cervix and expel the foetus through the birth canal. The l …

Present the mechanism explicitly as a loop, not a straight chain: identify the starting stimulus, the hormone released, what that hormone does, and how that effect feeds back to increase the original stimulus -- and name it as pos …

Describing parturition as driven by ordinary negative feedback like most other hormonal loops -- parturition is a deliberately-noted exception, where rising oxytocin/stretch drives even more oxytocin release rather than suppressing it, and this …