Lactation

Lactation is controlled by hormone. Prolactin, the hormone needed for milk production, is not secreted during pregnancy, due to the high levels of estrogen and progesterone. After birth, however, the pituitary of the mother starts to produce prolactin. Thus, milk is made.
When the baby sucks the mother's nipples, sensory neurons send the information to the hypothalamus, that will produce oxytocin, and then send to the pituitary, whom will release it. The oxytocin stimulates the movement of the milk, by causing the mammary lobules to contract.