Neuroendocrine Regulation of Lactation and Milk Ejection

Milk is a secretion of the mammary gland that supplies all of the necessary nutrients for survival of mammalian species. Secretion of milk, or lactation, is the final stage of the reproductive cycle and is completely dependent on secretion of numerous hormones, many of which are, in turn, regulated by the neuroendocrine system. These hormones are responsible for growth of the mammary gland, for initiating secretion of milk at the time of parturition (lactogenesis), and for maintaining secretion of milk in the postpartum period (galactopoiesis) of the reproductive cycle. After milk is secreted from epithelial cells of the mammary gland, it is stored in the lumen of the alveoli and ducts of the gland and then removed in response to suckling or milking. Removal of milk from the mammary gland requires milk ejection, which is a classical neuroendocrine reflex. After a brief description of the anatomy of the mammary gland and the growth patterns of the mammary glandthrough the life cycle of a mammal, the major thrust of this chapter will be to describe hormonal and neuroendocrine regulation of mammary growth, lactogenesis, maintenance of lactation, and milk ejection.