Ultrastructure of the human mammary ductule

Abstract

Terminal ductules of resting premenopausal breast were studied to determine the limits of normal ultrastructural variability. The lumen of the ductule is enclosed by columnar epithelial cells; and these, in turn, are enclosed by a discontinuous layer of myoepithelial cells. Some epithelial cells extend from the lumen through the discontinuities among the myoepithelial cells to the basement membrane. Usually, ductules with closely apposed cells have simple basement membranes, while those with separated cells have multiple basement membranes. Microvilli are present in clear spaces in lumens and between cells but are absent from occluded lumens. Some lumens contain orderly arrangements of filamentous material of maximum unit diameter of 410 Å. Both cell types vary in density from light to dark. Two types of nuclear inclusion are found. Position, smaller mitochondria, hemidesmosomes and dark patches on myofibrils distinguish myoepithelial from epithelial cells. The distinctions are quantitative rather than qualitative, and there are suggestions of an essential similarity between the 2 cell types. Copyright © 1969 American Cancer Society