The specimen shown here is from a lactating mammary gland. It is similar in appearance to the gland at the late proliferative stage but differs mainly to the extent that the alveoli are more uniform in appearance and their lumina are larger. As in the late proliferative stage, several alveoli can be seen merging with one another (asterisks). The use of osmium in this specimen stains the lipid component of the secretion. The inset reveals the lipid droplets within the epithelial cell cytoplasm as well as lipid that has been secreted into the lumen appearance to the alveolar epithelium. The cells of both components are secretory. The alveoli as well as the intralobular ducts consist of a single layer of cuboidal epithelial cells subtended by myoepithelial cells. Often, what appear to be several alveoli are seen merging with one another (asterisks). Such profiles represent alveolar units opening into a duct. Interlobular ducts are easy to identify as they are surrounded by dense connective tissue. In one instance, an intralobular duct can be seen emptying into an interlobular duct (arrow). The inset shows the secretory epithelium at a much higher magnification. Note that it is a simple columnar epithelium. The nucleus of a myoepithelial cell (M) is seen at the base of the epithelium. Generally, these cells are difficult to recognize. Also, as noted above, numerous plasma cells (P) and lymphocytes (Ly) are present in the loose connective tissue of the lobule.
of the alveolus. The lipid first appears as small droplets within the epithelial cells. These droplets become larger and ultimately are secreted into the alveolar lumen along with milk proteins. The milk proteins are present in small vacuoles in the apical part of the cell but cannot be seen by light microscopic methods. They are secreted by exocytosis. The lipid droplets, in contrast, are large and surrounded by the apical cell membrane as they are pinched off to enter the lumen; thus it is an apocrine secretion. Several interlobular ducts are evident. One of these ducts reveals a small branch, an ending intralobular duct (arrows) joining the interlobular duct.
D, interlobular duct Ly, lymphocyte M, myoepithelial cell P, plasma cell S, connective tissue septa TDLU, terminal duct lobular unit arrow, union of intralobular duct with interlobular duct asterisks, sites of merging alveoli KEY
PLATE 103 • MAMMARY GLAND, LATE PROLIFERATIVE AND LACTATING STAGES TDLUTDLUTDLU TDLUTDLUTDLU TDLUTDLUTDLU DDD MMM *** *** *** *** *** *** *** *** DDDDD DDDD LyLyPPLy P SSS SSS
OVERVIEW OF THE EYE / 896 GENERAL STRUCTURE OF THE EYE / 896 Layers of the Eye / 896 Chambers of the Eye / 897 Development of the Eye / 898 MICROSCOPIC STRUCTURE OF THE EYE / 899 Corneoscleral Coat / 899 Vascular Coat (Uvea) / 902 Retina / 907 Crystalline Lens / 915 Vitreous Body / 915 Accessory Structures of the Eye / 916 Folder 24.1 Clinical Correlation: Glaucoma / 905 Folder 24.2 Clinical Correlation: Retinal Detachment / 908 Folder 24.3 Clinical Correlation: Age-Related Macular Degeneration (ARMD) / 909 Folder 24.4 Clinical Correlation: Conjunctivitis / 917