histology of breast

8/10/2019 Histology of Breast

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Histology of Breast


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Alveolar development in the breast during pregnancy. The micrographs show the major changes in the mammary glands during

pregnancy and lactation that involve mainly the secretory alveoli, lobules and ducts. (a): The mammary glands of adult, nonpregnant

women are inactive, with small ducts and few lobules (L) having secretory alveoli which are not welldeveloped. The structure with the

large lumen in each lobule is part of the duct; the smaller structures are the small, undeveloped alveoli. The breasts are composed

largely of connective tissue (CT), having considerable fat. (b): The glands become active during pregnancy, with the duct system growing

rapidly and the secretory units of each lobule becoming much larger and more extensively branched. In this micrograph adipocytes (A)

are included but these are only a small fraction of those present. (c): During lactation, the lobules are greatly enlarged and the lumens

of both the numerous glandular alveoli (A) and the excretory ducts (D) are filled with milk. The protein content of milk makes it

eosinophilic in histological sections. At this time the intralobular connective tissue is more sparse and difficult to see, except for small

septa (arrows). All X60, H&E.


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Active versus lactating alveoli. Glandular alveoli develop completely only during pregnancy and begin milkproduction near the end of pregnancy. (a): Micrograph shows alveoli (A) develop as spherical structures composedof cuboidal epithelial cells surrounded by the contractile processes of myoepithelial cells (M). Development occurs

at different rates throughout the breast. Late in pregnancy lymphocytes (L) leave venules (V), accumulate in theintralobular connective tissue and differentiate as plasma cells (P). IgA secreted by these cells is transferred intomilk and helps confer passive immunity from the mother to the nursing infant. A small amount of milk is beginningto accumulate in the lumen of the duct (arrow). X400. H&E. (b): Micrograph from a plastic section shows secretorycells of the lactating gland,to be more columnar and contain variously sized lipid droplets, which are also visible inthe milk (LD). Connective tissue appears less cellular, although blood vessels (V) and lymphocytes remain present.Secretory cells in the enclosed area are shown diagrammatically in Figure 2226. X400. PT.


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Secretion in the mammary gland. Alveolar cells of the lactating mammary gland are highly active in

protein synthesis on rough ER and lipid synthesis. Most proteins are packaged into secretoryvesicles in the Golgi apparatus and secreted at the apical end of the cells by typical exocytosis ormerocrine secretion. Lipids coalesce as free cytoplasmic droplets. These grow in size and eventuallyundergo aprcrine secretion, in which they are extruded from the cell along a portion of the apicalcell membrane (and often a small amount of attached cytoplasm.) Both types of secretion areshown here in a sequence moving from left to right. Similar cells are seen in the enclosed area inthe light micrograph shown in Figure 2224.


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Apoptosis during postlactational mammary gland regression. Afterweaning, all glandular alveoli of the breast regress, as shown in thisplastic section of a single alveolus. The secretory cells now have alow cuboidal structure and many cells are undergoing apoptosis andhave sloughed into the lumen. Milk with lipid droplets is also stillpresent there. The dead cells and other tissue debris are removedby macrophages. X400. PT.

histology of breast

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