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United States Department of Agriculture

Agricultural Research Service

Title: Physiology of lactation

item Hopkinson, Judy
item Schanler, Richard

Submitted to: Electronic Publication
Publication Type: Popular Publication
Publication Acceptance Date: 5/11/2005
Publication Date: 5/11/2005
Citation: Hopkinson, J., Schanler, R.J. 2005. Physiology of lactation. UpToDate Online Journal [serial online]. 14.3. Available:

Interpretive Summary: Physicians are expected to offer guidance and medical care for lactating women and breastfed infants. In order to provide quality evidence-based care, they must keep up with a vast medical and scientific literature on this topic, as well as hundreds of other medical topics. Up-To-Date is an on-line publication that provides physicians with comprehensive summaries of the literature covering background material and incorporating each new scientific discovery as it is published. Physicians use this and a handful of similar resources to provide the highest quality, evidence-based care to the public. Scientists familiar with each topic area author and maintain these reviews. This particular article explains current understanding of the physiology of human lactation and the scientific data on which that understanding is based.

Technical Abstract: The breast changes in size, shape, and function during puberty, pregnancy, and lactation. The physiology of lactation is reviewed here. The breast is composed of fat and connective tissue that supports a tubuloalveolar structure. During development, anatomic changes involving new lobule formation and maturation occur in puberty, pregnancy and lactation. Milk production or lactogenesis occurs in two stages. Stage I or secretory initiation takes place during the second half of pregnancy with the formation of fully differentiated secretory units and production of small amounts of milk. Stage II or secretory activation is marked by the onset of copious milk production after delivery. Milk is a complex fluid with both chemical and cellular components. The synthesis and secretion of components that make up breast milk are carried out by the following five processes: exocytosis, reverse pinocytosis, transcytosis, apical transport, and paracellular movement. Milk production is primarily regulated by the emptying of the breast. Other important factors include prolactin levels, feedback inhibition and lactose synthesis. Myoepithelial cell contraction, under the influence of oxytocin forces milk into the ducts from the alveolar lumens.

Last Modified: 06/26/2017
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