What is the MER (Milk Ejection Reflex) or “Let-Down”?
In between feedings, the clusters of alveoli and the milk ducts fill up with milk. This makes the breasts feel heavy when it is time for the baby to nurse. As the baby sucks, stimulation of the nipple causes the mothers pituitary gland, located in the brain, to release oxytocin. Oxytocin causes contractions in the muscle cells that surround the alveoli. These contractions squeeze milk out of the alveoli and cause the ducts to expand, pushing milk toward the nipple. In a beautiful system of give and take, the breast propels milk as the baby sucks. Some mothers can feel this hormonally induced release. They describe it as a tingling or rushing sensation. Surprising at first, most women come to experience it as a pleasant, and soothing sensation. This is referred to as the let-down, or milk ejection reflex (MER). There are mothers who do not experience the sensation directly, but observe that the other breast will begin to leak or the baby will start to gulp. Other signs that a milk eject
