Mammary glands are the accessory reproductive glands within the breasts that function in milk production. Fifteen to twenty-five lobes of glandular tissue containing mammary alveoli synthesize and secrete the milk in the mammary glands, a process known as lactation. The milk is transferred via a system of lactiferous ducts that converge to the nipple. Ligamentous and fatty tissue surround the ducts and give support and shape to the breasts.

Lactation begins after delivery of a baby. The initial secretion of the mammary glands before true lactation begins is termed colostrum. Colostrum is a thin yellowish fluid that contains proteins and immunoglobins, which initiates temporary passive immunity in the newborn. Delivery of the placenta decreases the levels of estrogen and progesterone that, in conjunction with prolactin, initiate the production of milk. In the days following delivery, milk production ceases and will only occur...