Q.(a) Explain the role of oxytocin and relaxin in parturition and lactation. OR

Parturition (childbirth) is triggered near term as rising oestrogen (relative to progesterone) increases uterine contractility beyond the weak Braxton-Hicks contractions of earlier pregnancy; foetal descent stretches the cervix, producing a neurohumoral Ferguson (foetal ejection) reflex that releases oxytocin from the posterior pituitary, driving the strong uterine contractions that expel the baby through the birth canal, followed by the placenta and cord remnants (the 'afterbirth'). Relaxin, from the placenta and corpus luteum, assists by relaxing the pelvic ligaments and dilating the cervix; when normal delivery is not possible, a Caesarean section is performed instead. Lactation is milk production by the mammary glands: rising oestrogen, progesterone and hPL late in pregnancy prime the hypothalamus and anterior pituitary to secrete prolactin, which drives milk synthesis (lactogenesis), while oxytocin ca …