Q.Explain the steps of parturition.

Prolactin is the key hormone that triggers and sustains milk production in the mammary glands after delivery.

During pregnancy, rising levels of oestrogen and progesterone promote growth and development of the mammary gland tissue, but these same high hormone levels also inhibit actual milk secretion. After childbirth, oestrogen and progesterone levels fall sharply, removing this inhibition, and prolactin (secreted by the anterior pituitary in response to the infant's suckling) becomes the dominant hormone driving and sustaining milk synthesis and secretion (lactogenesis), and its continued release (stimulated by ongoing suckling) maintains lactation throughout the nursing period. Oestrogen mainly promotes duct development, FSH regulates ovarian follicle growth (not lactation), and oxytocin, while important for lactation, acts specifically to cause contraction of myoepithelial cells around the alveoli, producing the milk-ejection/let-down reflex, rather than initiating milk synthesis itself.

Relaxin relaxes the pelvic ligaments and muscles during parturition (childbirth).

Relaxin, produced mainly by the ovary/placenta near term, loosens the pubic symphysis and pelvic ligaments and softens the cervix, allowing the pelvis to widen and the baby to pass through the birth canal more easily.

Why the others are wrong: insulin regulates blood glucose; adrenaline is the 'fight-or-flight' hormone; thyroxine controls metabolism — none relax the pelvic organs for delivery.

Oxytocin is the "rapid birth hormone" that causes the strong uterine contractions of labour.

Oxytocin is secreted by the posterior pituitary (from hypothalamic neurosecretory cells) and acts on the myometrium of the uterus, causing powerful rhythmic contractions that expel the foetus during parturition — a classic positive-feedback loop, where stretching of the cervix further stimulates oxytocin release. Insulin and glucagon are pancreatic hormones that regulate blood glucose and have no role in birth; vasopressin (ADH) regulates water reabsorption in the kidney, not uterine contraction.