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Anatomy and Physiology of Lactation

2001; Elsevier BV; Volume: 48; Issue: 1 Linguagem: Inglês

10.1016/s0031-3955(05)70283-2

1557-8240

Margaret C. Neville,

Neonatal Respiratory Health Research

The defining characteristic of all animals of the class Mammalia is the provision of milk, a fluid the composition of which exactly mirrors the needs of the young of the species. Although the location and external form of the mammary glands differ among species, the general phases of development and the mechanisms of milk production are remarkably similar. For this reason, researchers have been able to draw on a myriad of work in animals to understand this process. In humans, milk is produced and stored in differentiated alveolar units, often called lobules, in the breast. The amount of milk produced is regulated by prolactin and local factors. Removal of milk from the breast is accomplished by a process called milk ejection, brought about by a neuroendocrine reflex that ends with the secretion of oxytocin from the posterior pituitary gland and its interaction with myoepithelial cells that surround the ducts and alveoli. In humans, the small ducts coalesce into 15 to 25 main ducts that drain sectors of the gland. The main ducts dilate into small sinuses as they near the areolus, where they open directly on the nipple. In this article, the developmental stages of the human mammary gland are described, followed by a discussion of the major principles of human milk secretion and ejection. Finally, interactions between lactation and maternal metabolism are outlined briefly, and the interaction of lactation with fertility is discussed. The transition from pregnancy to lactation, called lactogenesis, is described in the article by Neville et al (p. 35) in this issue.