Page 897 - Atlas of Histology with Functional Correlations

FIGURE 21.39 | Mammary Gland During

Proliferation and Early Pregnancy

For milk secretion (lactation), the mammary gland undergoes structural changes.
During the first half of the pregnancy, the intralobular ducts undergo

proliferation and form terminal buds that differentiate into alveoli (2, 7). At this
stage, most of the alveoli are empty, and it is difficult to distinguish between the
small intralobular excretory ducts (10) and the alveoli (2, 7). The intralobular
excretory ducts (10) appear more regular with a more distinct epithelial lining.

The intralobular excretory ducts (10) and the alveoli (2, 7) are lined with two
layers of cells, the luminal epithelium and a basal layer of flattened
myoepithelial cells (8).

A loose intralobular connective tissue (1, 9) surrounds the alveoli (2, 7)

and the ducts (10); a denser connective tissue with adipose cells (6) surrounds
the individual lobules and forms interlobular connective tissue septa (3). The
interlobular excretory ducts (4, 11), lined with taller columnar cells, course in
the interlobular connective tissue septa (3) to join the larger lactiferous duct (5)
that is lined with a low pseudostratified columnar epithelium. Each lactiferous

duct (5) collects the secretory product from the lobe and transports it to the
nipple.

FIGURE 21.39 ■ Mammary gland during proliferation and early pregnancy.
Stain: hematoxylin and eosin. Left, medium magnification; right, high
magnification.

FIGURE 21.40 | Mammary Gland During

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