Lactation is the expression of milk from mammary glands. Breast milk production is controlled by two hormones: prolactin and oxytocin. Once the infant (or offspring) suckles on the female's breast, a signal is sent to the brain, which triggers the production of the two hormones. While the secretion of prolactin leads to the production of milk in the alveoli, oxytocin causes the milk flow from the alveoli to the ducts (World Health Organization. 2009).