Parturition
பிரசவம்
Parturition is not a passive event; it is a complex neuroendocrine reflex. The fetus, not the mother, initiates the signal for its own birth. If you confuse the source of the Fetal Ejection Reflex, you lose marks.
The idea
Parturition is induced by a complex neuroendocrine mechanism. The signals originate from the fully developed fetus and placenta, inducing mild uterine contractions called the Fetal Ejection Reflex. This triggers the release of oxytocin from the maternal posterior pituitary. Oxytocin acts on the uterine muscle to cause stronger contractions, which in turn stimulates further oxytocin secretion, creating a positive feedback loop.
Why it matters
It is the biological mechanism to expel the fully developed fetus from the uterus into the external environment.
NEET lens
NEET focuses on the 'Fetal Ejection Reflex' and the 'Positive Feedback Loop'. Remember: Oxytocin comes from the mother's pituitary, but the signal starts from the fetus. Do not confuse this with negative feedback mechanisms like those in blood glucose regulation. Expect questions on the sequence of events: Fetus -> Placenta -> Pituitary -> Oxytocin -> Uterine Contraction.
Clinical significance
Failure of this neuroendocrine reflex leads to prolonged labor or uterine inertia. In such cases, synthetic oxytocin (Pitocin) must be administered intravenously to induce or augment contractions. Without this intervention, fetal distress or maternal hemorrhage becomes a life-threatening risk.
Introduction
Parturition is the process of childbirth — the expulsion of the fetus and placenta from the uterus at the end of pregnancy (~40 weeks), initiated by a hormonal cascade involving oxytocin, prostaglandins, and corticosteroids, driven by a positive feedback loop.
Core concept
Trigger: fetal hypothalamus-pituitary axis matures → fetal ACTH → fetal adrenal cortex → corticosteroids → placenta shifts from progesterone to estrogen production → estrogen: (1) increases oxytocin receptors on uterus, (2) stimulates prostaglandin synthesis. Parturition cascade: Mild uterine contractions → fetal head pushes cervix → cervix stretches → Ferguson reflex → more oxytocin released → stronger contractions → positive feedback loop → intensifying contractions. Stages of labour: (1) Stage 1: cervical dilation (0→10 cm), longest, ~8-12 hours first labour. (2) Stage 2: fetal expulsion (pushing), 30 min–2 hours. (3) Stage 3: placental delivery (afterbirth), 5-30 min after baby. Relaxin hormone: from corpus luteum and placenta → relaxes pubic symphysis + cervix.
Go deeper
Oxytocin positive feedback: uterine contraction → cervical distension → more oxytocin → more contraction. This is one of the clearest examples of positive feedback in physiology. Oxytocin is used clinically (Pitocin) to induce or augment labor when natural onset is slow.
From Class 10
After ~9 months of pregnancy, the baby is ready to be born. The process of childbirth — contractions that push the baby out — is called parturition.