How Your Body Makes Milk
Your body started preparing to make milk while you were still just a fetus. Both male and female infants have mammary glands and a rudimentary ductal system at birth. Some newborns even secrete small amounts of milk as a reaction to maternal hormones circulating in their blood. However, this reaction is temporary. The female breast continues to develop well into adulthood.
The Milk Making System
The structure within our breasts that makes and delivers milk has been likened to a tree. Each breast contains many trees, which grow up from the nipple. Further up, a network of branches grows from the trunk and these branches are covered in leaves. The leaves are actually alveoli, the structure that produces the milk. They are framed by other cells that cause the milk to flow into the branches, or ductules, through the trunk, the duct, and out one of the many holes in the nipple. Each tree is called a lobe and is surrounded by fat. It is the fat that gives the breast its shape and size.
The duct system mentioned above begins developing when a girl hits puberty. With every menstrual cycle, more branches grow on the trees. The most significant development occurs during pregnancy when the alveoli multiply and grow. It is like the tree filling out with leaves. Your breasts will probably grow and be tender. These are positive signs that all is working well.
Milk Production
Our breasts begin producing colostrum around 12 to 16 weeks into the pregnancy. This is the milk that your baby will receive until your body begins producing mature milk. Delivery of the placenta triggers hormones in your body to start producing mature milk. This process takes a few days. At this point, your body does not know how much milk to make or even if it needs to feed one baby or triplets. Many women have too much milk around the 3rd or 4th day postpartum. Frequent feeding helps to relieve the fullness and sets your body up to produce enough milk for your baby for the next six months.
Milk Delivery
As you breastfeed your baby, your brain receives the message to produce a hormone called oxytocin, which causes the alveoli to compress and literally squeeze out the milk. The milk flows down the ducts and through the nipple. You might even see it spray out of your breast. This is called the Milk Ejection Reflex (MER). Your MER can be triggered by your baby's cry as well as her touch and sometimes just by thinking about her. In general though, the more milk you have, the stronger it will flow. On the other hand, if you have lost sensitivity in your nipples though surgery or nerve damage, your MER will be impaired.
Fooling Mother Nature
You do not have to experience pregnancy and birth in order to breastfeed. There are ways to get the right hormones to produce milk for adopted children. This is called "induced lactation." A board certified lactation consultant or doctor of breastfeeding medicine can help you reach your goals.