Published online by Cambridge University Press: 16 May 2011
Introduction
Mammary glands do not normally feature prominently in discussions of reproduction. Instead, discussions of reproduction deservedly emphasize the primary sex organs, the reproductive tract and the cardinal hormones (gonadotrophins and gonadal steroids) involved. However, newborn mammals cannot process foraged food and only the mammary gland is capable of synthesizing renewable food, in the form of milk, which is digestible by the neonates. Milk is a complex nutrient, consisting mainly of milk sugar (lactose), lipids, the milk proteins (casein and whey) as well as monovalent and divalent cations and immune antibodies. The female mammary glands are markedly altered functionally and morphologically during pregnancy in preparation for the production of this complex liquid food mixture for delivery to the neonates. The mammary gland thus forms an important adjunct to the mammalian reproductive system and is essential for the survival of mammalian species.
The conversion from inactive to active milk-producing mammary tissues requires extensive surges in cell proliferation as well as metabolic modifications. These alterations occur regularly during each ovulatory cycle in preparation for a potential pregnancy and the post-partum lactational activity.
In the absence of pregnancy, the proliferative rate returns to basal levels in the normal breast. The regulation of these proliferative oscillations depends on the steroid hormone milieu within microregions of the breast. It is argued that dysregulation of this microenvironment can lead to conditions within regions of the breast that result in foci of neoplasia.
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