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Summary Human Mouse

2.1.1. Early Development of the Human Breast

The human mammary gland, as with all mammals, originates from the milk line that extends bilaterally from the axilla to the groin. In humans, two milk buds form during early fetal development and extend into the fat pad stroma to form ducts.

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	The milk line develops in the fetus extending from the axilla to the groin as an epidermally derived structure from the skin. The slide shows a transverse section with early branching of the major lactiferous ducts. Epon embedded toluidine blue staining.		In females a doughnut shaped disk of stroma, into which the branching duct tree descends, is forming several years before the onset of menses. This 2mm thick slice of breast shows the blue staining of the epithelium since nuclei stain with the hematoxylin. Note the early formation of lobules around one of the ducts and the convergence of the major lactiferous ducts at the nipple.
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	As the breast enlarges the dense connective tissue stroma is dispersed by fat.		The darkly stained small round, grape-like masses are the cellular lobules, the hormone sensitive, potentially milk producing microorgans. They stain blue since hematoxylin stains the nuclei. Each is 1-2mm in diameter. A breast contains thousands of lobules in young adult females.