Glandular epithelial and myoepithelial cells are the most important cells associated with mammary ducts and lobules. Glandular epithelial cells line the duct system, whereas myoepithelial cells lie deep within the epithelium between the epithelial cells and the basal lamina. These cells, arranged in a basketlike network, are present in the secretory portions of the gland. In routine hematoxylin and eosin (H&E) preparation, the myoepithelial cells are more apparent in the larger ducts. However, in the immunocytochemical preparation, their discontinuous, basketlike arrangement is better visualized within the alveoli (Fig. 23.33). Contraction of myoepithelial cells assists in milk ejection during lactation. Recent immunoﬂuorescence studies have proven that breast progenitor cells found in the ductular epithelium give rise to both glandular cells of the alveoli and myoepithelial cells.
The morphology of the secretory portion of the mammary gland varies with the menstrual cycle.
FIGURE 23.31 • Photomicrographs of a section through the female nipple. a. This low-magnification micrograph of an H&E–stained sagittal section through the nipple shows the wrinkled surface contour, a thin stratified squamous epithelium, and associated sebaceous glands (arrows). The core of the nipple consists of dense connective tissue, smooth muscle bundles, and the lactiferous ducts that open at the nipple surface. 6. b. The wall of one of the lactiferous ducts is shown here at higher magnification. Its epithelium is stratified cuboidal, consisting of two-cell layers. As it approaches the tip of the nipple, it changes to a stratified squamous epithelium and becomes continuous with the epidermis. 175. c. A higher magnification of the sebaceous gland from the rectangle in a. Note how the glandular epithelium is continuous with the epidermis (arrows), and the sebum is being secreted onto the epidermal surface. 90. d. A higher magnification showing bundles of smooth muscle in longitudinal and cross-sectional profiles. 350.
In the inactive gland, the glandular component is sparse and ductules appear as cords formed by the cuboidal-shaped epconsists chiefly of duct elements (Fig. 23.34 and Plate 102, ithelial cells with little or no lumen. During the luteal phase, page 892). During the menstrual cycle, the inactive breast the epithelial cells increase in height, and lumina appear in undergoes slight cyclic changes. Early during the follicular the ducts as small amounts of secretions accumulate. Also, phase, the intralobular stroma is less dense, and terminal fluid accumulates in the connective tissue. This is followed by
FIGURE 23.32 • Terminal Duct Lobular Unit a. This schematic diagram shows components of the terminal duct lobular unit (TDLU). Terminal ductules and intralobular collecting duct are surrounded by a specialized hormonally sensitive loose connective tissue called intralobular stroma. TDLU are separated from each other by interlobular stroma containing variable amount of dense irregular connective tissue and adipose tissue. In active mammary glands, terminal ductules differentiate into milk-producing alveoli. b. This photomicrograph shows the TDLU from an inactive mammary gland. The clear area in the upper part of the image represents adipose cells. 120.
FIGURE 23.33 • Myoepithelial cells in the mammary gland.