Page 899 - Atlas of Histology with Functional Correlations

decreases, whereas the interlobular connective tissue (3, 9) increases because

of the enlargement of the glandular tissue. Surrounding the alveoli are flattened
myoepithelial cells (10, 12), more visible in the higher magnification on the
right. Located in the interlobular connective tissue (3, 9) are the interlobular
excretory ducts (7, 13), lactiferous ducts (14) with secretory product in their
lumina, various types of blood vessels (5), and adipose cells (6).

FIGURE 21.41 ■ Mammary gland during late pregnancy. Stain: hematoxylin

and eosin. Left, medium magnification; right, high magnification.

FIGURE 21.42 | Mammary Gland During

Lactation

This illustration of a mammary gland shows in greater detail the structure of
alveoli during lactation at both lower (left) and higher (right) magnifications.

A lactating mammary gland exhibits distended alveoli filled with secretions

and vacuoles (1, 5, 9) with some showing irregular branching (1). Because of
increased size of the glandular epithelium (alveoli) and adipose cells (10), the
interlobular connective tissue (3, 7) is reduced when compared to the inactive
gland (Figs. 21.37 and 21.38)

During lactation, not all of the alveoli exhibit secretory activity. The active

alveoli (1, 5, 9) are lined with a low epithelium and filled with milk that appears
as eosinophilic (pink) material with vacuoles of dissolved fat droplets (1, 5, 9).
Some alveoli accumulate secretory product in their cytoplasm, and their apices
appear vacuolated, or light staining, because of the removal of fat during tissue

preparation. Other alveoli appear inactive (4) with empty lumina lined with a

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