A new mother tells you that when she nurses her baby, she feels as if she is having menstrual cramps. How would you explain this phenomenon?
During nursing, the mechanical stimulus of suckling triggers a neural reflex that leads to the release of oxytocin from the posterior pituitary. Oxytocin enters the bloodstream and stimulates contractile cells that surround the secretory cells in the mammary glands to contract and move milk into the lactiferous sinuses—the milk let-down reflex. Oxytocin also stimulates smooth muscle cells of the myometrium, so the rise in oxytocin sometimes leads to uterine contractions as well, producing a feeling similar to menstrual cramping. The uterine contractions help stem uterine bleeding.
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