The lobules, as you can see in the picture, group together, forming larger units called lobes. The average breast has between 15 and 20 lobes, which form a spoke pattern originating from the nipple/areola area.
The lobes run into the (milk)ducts which continue through the breast towards the nipple. Once arrived at the nipple, the ducts merge into 6 to 10 larger ducts, called collecting ducts, which connect to the outside.
Lymph nodes run through the entire body, and act as filters for foreign particles, such as cancer cells. The lymph nodes found around the armpit are the most important when it comes to diagnosing breast cancer. Because breast cancer often first spreads to the lymph nodes in the armpit, from the breasts, doctors can determine which stage the breast cancer is in, and in turn, determine the treatment.
The breasts of younger women are mainly made up of glandular tissue, with on average only a small percentage being fat (depending on the woman general percentage of body fat). Therefore the breasts are firmer than in older counterparts. As women grow older, especially due to the loss of estrogen at menopause, the lobes shrivel and are replaced by fat. The breasts become softer, and lose their support. Physical examination and mammography are easier to interpret and are also more accurate.
All components of the breast are influenced by hormones, the glandular tissue being the most sensitive. Very dramatic and totally normal changes can occur in the consistency of the breasts during the menstrual cycle. These changes are most pronounced just before the menstruation, when levels of estrogen and progesterone are at their highest. Right after menstruation, hormone levels are at their lowest and the breast becomes softer and less tender. This is also the best time to perform a self-breast exam or mammogram.
In post menopausal women, who are not taking estrogen supplementation, weight becomes a significant factor in the size and appearance of the breasts. Being mostly composed of fat at this point, small changes in body weight can produce significant changes in breast size.