Growth and development of breasts occur around the time of puberty in a girl. Breasts especially change during pregnancy by developing glands. These glands are connected to the nipple by small tubes. The secretion and ejection of milk is under hormonal control, which is ultimately controlled by the brain. When the baby is born a hormone called prolactin stimulates the milk forming glands to produce milk. The baby’s sucking sends messages to the brain which releases a hormone called oxytocin. This makes the muscular walls of the milk producing cells contract. Then the milk ejects down the duct and out through the nipples so that the baby gets a continuous supply of milk while sucking.See more..