The mamma consists of gland tissue; of fibrous tissue, connecting
its lobes; and of fatty tissue in the intervals between the lobes. The gland
tissue, when freed from fibrous tissue and fat, is of a pale reddish color,
firm in texture, flattened from before backward and thicker in the center than
at the circumference. The subcutaneous surface of the mamma presents numerous
irregular processes which project toward the skin and are joined to it by bands
of connective tissue. It consists of numerous lobes, and these are composed
of lobules, connected together by areolar tissue, bloodvessels, and ducts. The
smallest lobules consist of a cluster of rounded alveoli, which open into the
smallest branches of the lactiferous ducts; these ducts unite to form larger
ducts, and these end in a single canal, corresponding with one of the chief
subdivisions of the gland. The number of excretory ducts varies from fifteen
to twenty; they are termed the tubuli lactiferi. They converge
toward the areola, beneath which they form dilatations or ampullę,
which serve as reservoirs for the milk, and, at the base of the papillę,
become contracted, and pursue a straight course to its summit, perforating it
by separate orifices considerably narrower than the ducts themselves. The ducts
are composed of areolar tissue containing longitudinal and transverse elastic
fibers; muscular fibers are entirely absent; they are lined by columnar epithelium
resting on a basement membrane. The epithelium of the mamma differs according
to the state of activity of the organ. In the gland of a woman who is not pregnant
or suckling, the alveoli are very small and solid, being filled with a mass
of granular polyhedral cells. During pregnancy the alveoli enlarge, and the
cells undergo rapid multiplication. At the commencement of lactation, the cells
in the center of the alveolus undergo fatty degeneration, and are eliminated
in the first milk, as colostrum corpuscles. The peripheral
cells of the alveolus remain, and form a single layer of granular, short columnar
cells, with spherical nuclei, lining the basement membrane. The cells, during
the state of activity of the gland, are capable of forming, in their interior,
oil globules, which are then ejected into the lumen of the alveolus, and constitute
the milk globules. When the acini are distended by the accumulation of the secretion
the lining epithelium becomes flattened.
FIG. 1172- Dissection of the lower half of the mamma during
the period of lactation. (Luschka.) Click on the image to see it full size.
FIG. 1173- Section of portion of mamma. Click on the image to see it full size.
The fibrous tissue invests the entire surface of the mamma,
and sends down septa between its lobes, connecting them together.
The fatty tissue covers the surface of the gland, and occupies
the interval between its lobes. It usually exists in considerable abundance,
and determines the form and size of the gland. There is no fat immediately beneath
the areola and papilla.
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