A Look at the Amazing Human Milk Factory
By Melissa Clark Vickers, IBCLC
What a marvelous thing the human breast is! It produces all of your baby’s nourishment for at least six months, provides protection from myriad diseases and calms the fussiest of babies. It works on the principle of supply and demand, producing as much milk in just the right composition as baby needs at the time. Let’s take a look at this ingenious factory:
If you look inside the breast, underneath the skin and embedded within fatty tissue, you’ll see what looks like a cluster of grapes with the stems joining to form larger branches all pointing toward the nipple. Each of the grapes is an alveolus (plural: alveoli), and it is here that milk is made from blood. Tiny muscle cells that contract to squeeze milk droplets into tubes or ducts that lead to larger branches surround each alveolus. As these branches come together, there are wider spaces, or sinuses, just behind the nipple that allow the milk to pool. When baby latches on, he’ll compress those sinuses and be rewarded with a mouthful of milk shooting through many tiny, pore-sized openings in the nipple.
Prolactin relaxes Mom and brings out the best in her.
In addition to the alveoli and the milk ducts, the breast has a network of nerves that transmit signals back and forth from the nipple to the brain that drive the whole factory. When Baby begins sucking at the breast, a message is sent to the brain to trigger the release of oxytocin and prolactin. Oxytocin makes the muscle cells around the alveoli contract to squeeze out the milk. This is the same hormone that causes the uterus to contract during labor. Prolactin causes more milk to be produced and also causes a wonderful feeling of well-being. Nicknamed the “mothering hormone,” prolactin relaxes Mom and brings out the best in her, helping her cope with the stresses of parenthood.
Invaders, Take Warning!
In addition to the milk-producing “equipment,” the breast is an antibody factory as well. It can begin producing these disease-fighters in response to whatever Mom has been exposed to, thereby protecting her baby from getting sick. And the breast makes antibodies not only to illnesses Mom has been exposed to but also to whatever Baby has been exposed. The simple act of nursing sends complex signals back and forth between breast and Baby to fight these invaders.
Just the “Fats,” Ma’am
The grapelike clusters of alveoli are surrounded by fatty tissue. This tissue supports and protects the alveoli and the other structures of the breast. Interestingly, the main difference between a small breast and a large breast is not the number of alveoli, but the amount of fat. This is why size makes little difference in a woman’s ability to produce enough milk for her baby.
The Bull’s-eye Approach
The most striking aspect of the breast’s outward appearance is the similarity to a target. A darker area called the areola, which darkens further during pregnancy, surrounds the nipple. Perhaps this is nature’s way of making the breast an easy target for a newborn to find. Just as breast size varies from woman to woman, so does the size of the areola. Some women have areolas barely the size of a quarter, while others may have areolas 3 to 4 inches across. Nature loves variety! Scattered around the nipple and areola are little bumps called Montgomery glands. The function of these glands is not completely understood, although they secrete an oil that discourages bacterial growth and keeps the skin lubricated. The oil from the Montgomery glands is chemically very similar to amniotic fluid and may help the newborn find that nipple for which he’s looking.
Poetry in Motion
Let’s put the pieces together and see how the system works, starting with the very first time the newborn is offered his mother’s breast. A newborn knows what he’s looking for, and provided his mom hasn’t had a lot of medications during labor and delivery that make him sleepy, he’ll be more than willing – and able – to find it. Fascinating research has been done recently where newborns have been allowed to “crawl” up their mothers’ bellies to find the nipples and then attach themselves. We don’t give newborns nearly enough credit for what they can do! Dr. Marshall H. Klaus and Phyllis H. Klaus, CSW, MFCC, describe this beautiful journey in their book, Your Amazing Newborn (Perseus Books Group, 2000):
“The infant usually begins with a time of rest and quiet alertness, during which he rarely cries and appears to take great pleasure in looking at his mother’s face. Around 30 to 40 minutes after birth, the newborn begins making mouthing movements, sometimes with lip smacking, and shortly after, saliva begins to pour down onto his chin. When placed on the mother’s abdomen, babies maneuver in their own ways to reach the nipple. They often use stepping motions of their legs to move ahead, while to move horizontally toward the nipple, they use small push-ups, lowering one arm first in the direction they wish to go. These efforts are interspersed with short rest periods. Sometimes babies change direction in midstream. These actions take effort and time. Parents find patience well worthwhile as they wait and observe their infant on his first journey” (p. 11).
Once Baby latches onto the breast, his sucking triggers the release of oxytocin and prolactin. The oxytocin, in addition to delivering the milk to Baby, causes the uterus to contract. This reduces the risk of bleeding after delivery and helps return the uterus to its pre-pregnancy size. New moms may notice some uterine cramping when they nurse. This is a good sign that Baby is nursing effectively enough to trigger those hormones.
Baby’s initial sucking at the breast is typically quite fast – almost a flutter. This triggers the letdown, and his sucking will change to a deeper and slower suck-swallow pattern. His jaws will be working, his ears will be wiggling and his tummy will be filling! After a few minutes of this slower pattern, he’ll rest a bit and then start sucking faster. Then the suck-swallows begin again. This is a sign that Mom is having multiple letdowns that trigger milk with higher fat content.