What triggers the milk ejection reflex in breastfeeding?

The milk ejection reflex, also known as the let-down reflex, is primarily triggered by the release of oxytocin. Oxytocin is a hormone produced by the posterior pituitary gland, and its release is stimulated by the infant's suckling at the breast. This hormone travels through the bloodstream to the mammary glands, where it causes the myoepithelial cells surrounding the alveoli to contract. This contraction forces milk from the alveoli through the ductal system towards the nipple, making it available for the nursing infant.

While the release of prolactin plays a critical role in milk production and helps maintain lactation, it does not directly trigger the milk ejection reflex. Increased pressure in the breast and the vibration of the nipple are physical sensations that might influence breastfeeding comfort or encourage suckling, but they are not the primary mechanisms responsible for initiating the physiological process of milk ejection. The key factor in triggering this reflex is indeed the action of oxytocin in response to suckling.