The main building parts of the female breast are nipple, lactiferous sinus, lobules, ducts, and stroma. The lobules are glands that are producing the milk. After being produced, the milk passes through the ducts. The ducts connect the lobules and the nipple. Stroma represents a fatty tissue that surrounds the ducts and lobules, lymphatic and blood vessels.
An adult woman has around 20 lobes in each breast. One lobe is built from 20 to 50 lobules. The ducts are attached to the lobules. Smaller ducts join together into the increasingly larger duct. Each breast has around 10 ducts systems, and each duct has its own popping at the nipple.
There is also muscle tissue present in the nipples. The muscle tissue allows the nipples to become erect in response to stimulation or breastfeeding. With the help of the muscle tissue found around the lobules, the milk is squeezed into the ducts.