Expressing Milk

Before Madonna made headlines for practicing Kabbalah, she was telling the world to "Express Yourself." Perhaps her song (and that infamous cone bra) served as inspiration for some new moms to express milk -- a term describing the removal of milk from the body, either manually or mechanically. To understand how women use breast pumps to express milk, let's review the basics of lactation.

After the placenta is discharged from the mother's womb as part of the birthing process, the hormone prolactin tells the mother's body to start producing milk. Her milk supply usually comes in three to five days after delivery, and the more milk that's removed (by child or pump), the more milk that comes in. Suckling triggers the body to produce another hormone, oxytocin, which contracts muscles near the milk glands and eventually causes milk ducts to widen, releasing milk from reserves located around the nipple [source: Davis]. This is known as the milk-ejection reflex (MER) or "let-down."

A baby sucks about 50 to 90 times per minute at the beginning of a feeding, slowing his or her pace once let-down occurs [source: Mark]. Breast pumps mimic this rhythm by cycling, the combination of creating and releasing suction. Most hospital-grade and at-home electric pumps follow a rate of 40 to 60 cycles per minute -- about one pull per second.

Breast pumps vary based on mechanics and manufacturers, but they all work on the same basic principles. A plastic or glass breastshield allows a vacuum to be applied to the breast. The cone- or funnel-shaped part of the breastshield, called the flange, sits over the nipple and areola to create a seal. With the creation of a vacuum around the nipple, air is pulled into the breastshield. The nipple is then drawn into the tunnel, and the areola is pressed against the flange [source: Knorr]. With a manual pump, the mother squeezes a lever or bulb to create and release suction -- a cycling effect that triggers let-down. Battery-powered and electric pumps use motors, which connect to the flanges with plastic tubing to create pull.

The diaphragm, which isn't part of some manual pumps, helps create suction and release. In some pumps, like many of the hospital-grade ones, the diaphragm also creates a barrier separating mother from suction source, preventing contamination [source: Knorr]. A detachable, membranous valve joins with the pump body to help maintain proper suction.

As the pump imitates a baby's nursing rhythm (initial rapid pulls followed by a slower, deeper phase), milk eventually flows. Storage bags and ready-to-feed bottles directly attach to the pump to collect milk.