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. 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.
It can begin producing these disease-fighters in response to whatever mom has been exposed to, thereby protecting her baby from getting sick. And, not only does the breast make antibodies 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. Not only does this system ensure that baby gets milk when he wants it, but it is also the basis for changing the amount of milk mom makes. This tissue supports and protects the alveoli and the other structures of the breast.