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The breasts are secondary reproductive glands of ectodermal origin. They are frequently referred to as modified sweat glands. Each breast lies on the superior aspect of the chest wall. In women, the breasts are the organs of lactation, whereas in men, the breasts are normally functionless and undeveloped.

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Histology

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The adult female breast contains glandular and ductal elements, stroma consisting of fibrous tissue that binds the individual lobes together and adipose tissue within and between the lobes.

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Each breast consists of 12–20 conical lobes. The base of each lobe is in close proximity to the ribs. The apex, which contains the major excretory duct of the lobe, is deep to the areola and nipple. In turn, each lobe consists of a group of lobules. The lobules have several lactiferous ducts, which unite to form a major duct that drains the lobes as they course toward the nipple–areolar complex. Each of the major ducts widens to form an ampulla as they travel toward the areola and then narrow at its individual opening in the nipple. The lobules are held in place by a meshwork of loose, fatty areolar tissue. The fatty tissue increases toward the periphery of the lobule and gives the breast its bulk and hemispheric shape.

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Approximately 80–85% of the normal breast is adipose tissue. The breast tissues are joined to the overlying skin and subcutaneous tissue by fibrous strands.

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In the nonpregnant, nonlactating breast, the alveoli are small and tightly packed. During pregnancy, the alveoli hypertrophy, and their lining cells proliferate in number. During lactation, the alveolar cells secrete proteins and lipids, which comprise breast milk.

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The deep surface of the breast lies on the fascia that covers the chest muscles. The fascial stroma, derived from the superficial fascia of the chest wall, is condensed into multiple bands that run from the breast into the subcutaneous tissues and the corium of the skin overlying the breast. These fascial bands—Cooper's ligaments—support the breast in its upright position on the chest wall. These bands may be distorted by a tumor, resulting in pathologic skin dimpling.

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Histologic Changes in the Female Breast during the Life Span

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In response to multiglandular stimulation during puberty, the female breast starts to enlarge and eventually assumes its conical or spherical shape. Growth is the result of an increase in acinar tissue, ductal size and branching, and deposits of adipose, the main factor in breast enlargement. Also during puberty, the nipple and areola enlarge. Smooth muscle fibers surround the base of the nipple, and the nipple becomes more sensitive to touch.

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Once menses is established, the breast undergoes a periodic premenstrual phase during which the acinar cells increase in number and size, the ductal lumens widen, and breast size and turgor increase slightly. Many women have breast tenderness during this phase of the menstrual ...

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