Female pelvic organs. The interior of each breast is divided into several sections called lobes, which are further subdivided into lobules. Each lobule contains milk-secreting glands cushioned by fat and fibrous connective tissue. An intricate system of tiny ducts arran ged like tree branches carries the milk produced by the glands to a collecting chamber immediately below the nipple. The entire breast is richly supplied with blood vessels, as well as sensory nerves that make them exceptionally sensitive.
Connective tissue attaches the breast to the pectoral muscles of the chest wall.
Although breast milk is not normally produced until the infant begins sucking, a woman's body anticipates the possibility of pregnancy every month. During the first half of the menstrual cycle, rising levels of estrogen stimulate the growth of new cell s in the glands, ducts, and fibrous tissue of the breast. This increase in cell activity is accompanied by an increase in blood flow to the breasts, which may be experienced as fullness, warmth, and, sometimes, tenderness. After ovulation, the second ovar ian hormone, progesterone, is released into the bloodstream. The secreting process then begins in the gland cells.