The Human Breast

Anatomy & Physiology
Each of these accessory reproductive glands lies on the superior surface of the chest wall lying mostly on top of the pectoralis major muscle. The glandular portions are basically modified sweat glands. In women, the breasts are responsible for lactation; in men, they are normally undeveloped and without function.

The breast is made of lobes of glandular tissue with associated ducts for transfer of the milk to the exterior and supportive fibrous and fatty tissue. About 80-85% of normal breast tissue is fat during the reproductive years. The 15-25 lobes are further divided into lobules containing alveoli (small saclike features) of secretory cells with smaller ducts that conduct the 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 and during lactation the cells secrete milk substances, i.e. proteins and lipids. Muscular cells surrounding the alveoli contract to express the milk during lactation. Breast tissue is supported by ligaments called Cooper’s ligaments that keep the breasts in their characteristic shape and postition. In the elderly or in pregnancy these ligaments become loose or stretched, respectively, and the breasts sag.

Reproductive hormones are important in the development of the breast in puberty and in lactation. Estrogen promotes the growth of the gland and ducts while progesterone stimulates the development of milk producing cells. Prolactin, released from the anterior pituitary gland, stimulates milk production. Oxytocin, released from the posterior pituitary in response to suckling, causes milk ejection from the lactating breast.

The lymphatic system drains the tissues of the breast of excess fluid. Lymph nodes along the pathway of drainage screen for foreign bodies such as bacteria or viruses. The lymph nodes can also become enlarged when migrating cancer cells get lodged in the nodes. This is why lymph nodes located in the arm pit are checked during a breast exam and why they are often cut out along with cancerous tissue in the treatment of breast cancer.

Puberty and Maturity
In response to hormone stimulation, the breasts enlarge due to the growth of ductal and alveolar tissues and an increase in fat deposits. The nipple and areola also enlarge and become more senstitive to touch. When the woman begins to menstruate, the breasts undergo a periodic premenstrual phase that varies with the individual but can include an increase in size, swelling and tenderness. The symptoms subside within a few days of the onset of bleeding. During pregnancy, the breasts increase in size dramatically due to the influence of progesterone. The nipple and areola become deeply pigmented and increase in size. Most of the fat is replaced by the necessary machinery to produce milk by late pregnancy. After delivery the breasts begin to secrete milk. The gland rapidly returns to the prepregnant state when nursing ceases. The postmenopausal breast may retain its shape but the milk producing machinery is mostly replaced by fat.

Lactation
The breasts become fully developed under the influence of estrogen, progesterone and prolactin during preganancy. Prolactin causes the production of milk, and oxytocin release (via the suckling reflex) causes the contraction of smooth muscle cells in the ducts to eject the milk from the nipple. The first secretion of the mammary gland after delivery is called colostrum. It contains more protein and less fat than subsequent milk and contains antibodies that impart some passive immunity to the infant. Most of the time it takes 1-3 days after delivery for milk production to reach appreciable levels. The drop in circulating estrogens and progesterone caused by the expulsion of the placenta at delivery initiates milk production. Estrogen antagonizes the positive effect of prolactin on milk production. The physical stimulation of suckling causes the release of oxytocin and stimulates prolactin secretion stimulating more milk production.

Benign Breast Tumors
These include fibroademoma, periductal fibromas (connective tissue tumor), intraductal epithelial tumor, retention cysts, lipomas (fatty tumor), chronic cystic mastitis and fat necrosis. Most often they occur during the reproductive period of life or just after. These are often difficult to distinguish from malignant tumors and must be watched for a change in size, or lymphatic involvement, in which case the growth should be cut out and examined. Mammograms, ultrasound, thermography and aspiration of cystic forms can aid in diagnosis.

Malignant Breast Tumors
Breast cancer is the most common type of cancer in women and is a major public health problem in the U.S. with 1 in 8 women expected to be diagnosed sometime during their lives. Cancers of the breast are treated by several measures dependent on the patients’ age, clinical status, the type and size of the tumor, the degree of spread, and the estrogen responsiveness of the tumor. Some 35% of cancer of the breast in women of childbearing age are estrogen-dependent, meaning that their continued growth is dependent on the presence of estrogen. Symptoms are often dramatically decreased by the removal of the ovaries, the major source of estrogen. Breast cancer in males occurs but is rare.

Risk factors associated with breast cancer are:

  • beginning menstruation early &/or late menopause.
  • no children or children born after age 30.
  • history of fibrocystic desease.
  • family history of breast cancer.

Breast cancer is usually detected by self exam where the woman finds a lump that is painless, non tender and movable. In more advanced cases the lump becomes anchored to the underlying muscle. The skin may show signs of the cancer by dimpling or retraction. Mammography, thermography, and ultrasound may be used for diagnosis. Breast biopsy is used for confimation of diagnosis. Treatment can include surgery in the form of lumpectomy or mastectomy, sometimes followed by radiation, chemotherapy or endocrine therapy.

Breast Self Exam
Many medical personnel can provide instruction for performing a breast self exam. This procedure should be done monthly shortly after the menstural period because the changes induced in the breast by progesterone may confuse results. The procedure should also be done monthly after menopause. If any abnomality is discovered, a physician should be contacted.
A physician will generally palpate the breasts in a similar manner during a physical exam. The basic steps include:

  • Lie down with one hand behind your head.
  • With the other hand, gently feel the extended breast,  pressing lightly, with flattened fingers. Begin at the outer axillary portion (near arm pit) and move in a circular clockwise pattern inwardly toward the nipple. Gently feel for lumps or thickenings. Remember to feel all parts of the breast, including the underarm area.
  • Repeat the same procedure sitting up with the hand still behind your head.
  • Repeat the above steps for the other breast.

Gynecomastia
This is breast development in the male caused by a shift in the estrogen:androgen ratio due to increased circulating estrogens or a decrease in circulating androgens. But there may be multiple causes. For instance, digoxin can cause gynecomastia infrequently because it is weakly estrogenic. The diuretic spironolactone can also cause gynecomastia.