How Does Breast Milk Production Work?

Alveoli

The female breast, prepregnancy, contains an entire network of milk ducts. Hormones released during pregnancy send a signal to these milk ducts: "We're going to be working soon, so get ready!" In response, the milk ducts multiply in number and increase in size. As the ducts grow, they branch off into separate canals, and at the end of each canal, or ductule, a cluster of alveoli forms. Picture a clump of grapes and you'll have an idea of the shape of a cluster of alveoli; they're just much smaller. These sacs are where the milk is actually made.

After birth, your body releases the hormone prolactin. This hormone is from your pituitary gland (which is in the brain); it sends a signal to your body to begin full milk production. The alveoli and milk duct systems are already in place, and your body has been ready and able to produce milk since sometime during your second trimester. It's common for pregnant women to leak some of the earliest milk, called colostrum, before the baby is born. But once the baby is born and the prolactin is released, the alveoli begin their work in earnest and produce enough milk to keep your newborn baby full and happy.

Milk Ducts

After the milk is produced in the alveoli, it simply needs to get to baby. When your body gets the signal that it's time to breastfeed (which can occur from simply hearing your baby cry or from the motion of the baby suckling), it releases oxytocin. This hormone causes the tiny muscles that surround the alveoli to contract and push the milk out of the alveoli and up into the milk ducts. The milk ducts flow from the alveoli all the way to the milk sinuses, which are located on the areola, the dark area surrounding the nipple.

Milk Sinuses

The milk sinuses are the means of getting milk from your breast into your baby's mouth. They are the tiny openings, like straws, that are located on the areola. When your baby creates a suction with his mouth, the milk is released from these openings and into baby's mouth.

Supply and Demand

The actual amount of milk a mother produces is usually simply a matter of supply and demand. The more you feed your baby, the more milk your body will produce. Usually your breasts will be very full, even painfully so, during the first few days of breastfeeding. This is because your body doesn't yet know how much milk is needed, so it is carefully producing enough for the most demanding eater. As you settle into a routine with your baby, your body will get the message of how much milk is needed and when. If you are very consistent and nurse, say, every 2 hours, you might find your milk automatically letting down on the 2-hour mark, even before you have started feeding.