Breastfeeding - How Breast Milk is Made

Knowing how the breast is made and how it works to produce milk can help you understand the breastfeeding process. The breast actually begins developing in the first few weeks of gestation, before birth. But the mammary gland, the gland that produces milk, does not become fully functional until lactation begins. When a woman's breasts become swollen during pregnancy, this is a sign that the mammary gland is getting ready to work. The breast itself is a gland that is composed of several parts, including glandular tissue, connective tissue, blood, lymph, nerves, and fatty tissue. Fatty tissue is what mostly affects the size of a woman's breast. Breast size does not have an effect on the amount of milk or the quality of milk a woman produces.

Milk is secreted from the alveoli cells. When the alveoli cells are stimulated by a hormone, they contract and push the milk into the ductules and down into larger milk ducts underneath the nipple and areola. When the baby's gums press on the areola and nipple, milk is squeezed into the baby's mouth. The nipple tissue protrudes and becomes firmer with stimulation, which makes it more flexible and easier for the baby to grasp in the mouth. In the diagram, you can see that each mammary gland forms a lobe in the breast. Each lobe consists of a single branch of alveoli and milk ducts that narrow into an opening in the nipple. Each breast has about seven to ten lobes.
The Role of Hormones

Hormones play a key role in breastfeeding. The increase of estrogen during pregnancy stimulates the ductules to grow. After delivery, estrogen levels drop and remain low in the first several months of breastfeeding. The increase of progesterone during pregnancy also causes the alveoli and lobes to grow. Prolactin, also called the "mothering hormone," is another hormone that is increased during pregnancy and adds to the growth of breast tissue. Prolactin levels also rise during feedings as the nipple is stimulated. As prolactin is released from the brain into the mother's bloodstream during breastfeeding, alveolar cells respond by making milk. Oxytocin is the other hormone that plays a vital role because it is necessary for the let-down, or milk-ejection reflex to occur. It stimulates the alveoli cells to contract so the milk can be pushed down into the ducts. Oxytocin also contracts the muscle of the uterus during and after birth, which helps the uterus to get back to its original size and lessens any bleeding a woman may have after giving birth. The release of both prolactin and oxytocin may be responsible in part for a mother's intense feeling of needing to be with her baby.