PHYSIOLOGY OF LACTATION
ANATOMY
The breast is made of lobes of glandular tissue, with associated ducts for transfer
of milk to the exterior and supportive fibrous and fatty tissue. On average, there
are 15–20 lobes in each breast, arranged roughly in a wheel-spoke pattern
emanating from the nipple area. The distribution of the lobes, however, is not
even.
There is a preponderance of glandular tissue in the upper outer portion of the
breast (responsible for the tenderness in this region that many women
experience prior to their menstrual cycle).
About 80–85% of normal breast tissue is fat during the reproductive years.
The 15–20 lobes are further divided into lobules containing alveoli (small
saclike features) of secretory cells with smaller ducts that conduct milk to
larger ducts and finally to a reservoir that lies just under the nipple. In the
nonpregnant, nonlactating breast, the alveoli are small.
During pregnancy, the alveoli enlarge; during lactation, the cells secrete milk
substances (proteins and lipids). With the release of oxytocin, the muscular
cells surrounding the alveoli contract to express the milk during lactation.
Ligaments called Cooper ligaments, which keep the breasts in their
characteristic shape and position, support breast tissue. In the elderly or
during pregnancy, these ligaments become loose or stretched, respectively,
and the breasts sag.
The lymphatic system drains excess fluid from the tissues of the breast into
the axillary nodes. Lymph nodes along the pathway of drainage screen for
Figure I-1-2. Sagittal View of Breast
foreign bodies such as bacteria or viruses