Breast
(Anatomy and Function)

Picture of the anatomy of the breast.

• The breast generally refers to the front of the chest and medically specifically to the mammary gland.
• (The word "mammary" comes from "mamma," the Greek and Latin word for the breast, which derives from the cry "mama" uttered by infants and young children, sometimes meaning "I want to feed at the breast.")

• The mammary gland is a milk-producing structure that is composed largely of fat cells (cells capable of storing fat). The fat deposits are laid down in the breast under the influence of the female hormone estrogen.
• Just as the surge of estrogens at adolescence encourages this process, androgens, such as testosterone, discourage it.
• Within the mammary gland there is a complex network of branching ducts (tubes or channels). These ducts exit from sac-like structures called lobules.
• The lobules in the breast are the glands that can produce milk in females when they receive the appropriate hormonal stimulation.
• The breast ducts transport milk from the lobules out to the nipple. The milk exits the ducts from the breast at the nipple.

Human breasts function somewhat differently than those of other primates. In other primates, the breasts grow only when the female is producing milk (lactating). When the non-human primate female has weaned her young, her breasts flatten back down. In humans, the breasts develop at adolescence usually well before any pregnancy has occurred and the breasts stay enlarged throughout the remainder of life.

During pregnancy the breasts grow further. This growth is much more uniform than that at adolescence. The breasts of women with small breasts tend to grow about as much during pregnancy as those of women with large breasts. The amount of milk-producing tissue is essentially the same. This is the reason that when milk production begins, small-breasted women produce as much milk as do large-breasted women.

The nipple becomes erect because of such stimuli as a cold environment, breastfeeding, and sexual activity. The nipple of the post-partum female is used by the infant to breastfeed.

The small darkened (pigmented) area around the nipple is called the areola. (The word "areola" is the diminutive of the Latin "area" meaning a small space.) In pregnancy the areola darkens further and spreads in size. The areola contains small modified sweat glands (Montgomery's glands) that secrete moisture that acts as a lubricant for breastfeeding.

The lobules and ducts in the breast are supported by surrounding fatty tissue and the suspensory ligaments of the breast. There are no muscles in the breast. However, the breast tissue is located on top of the muscles of the chest wall. The characteristic bounce of the breast comes from the elasticity of the matrix of connective tissue fibers in the breast.

There are blood vessels and lymphatic vessels in the breast. The lymphatic vessels are thin channels similar to blood vessels; they do not carry blood but collect and carry tissue fluid which ultimately re-enters the blood stream. Breast tissue fluid drains through the lymphatics into the lymph nodes located in the underarm (axilla) and behind the breast bone (sternum).

Although the primary biologic function of the breast is to produce milk to feed a baby, the breast has for many centuries been a symbol of femininity and beauty.

Despite the contemporary concept of an ideal breast, there is no single model that is ideal. The appearance of the normal female breast differs greatly from one woman to another woman, and the breast of any given woman even differs at different times during the woman's life -- before, during and after adolescence, during pregnancy, during the menstrual cycle, and after menopause.

Breast tissue begins to originate by the fourth week of fetal life. It grows along two ridges, one on either side, running from the armpit (axilla) to the groin. These are the so-called milk ridges or milk lines. Breast tissue can develop anywhere along the milk line. It is quite common to have breast tissue up toward and even in the armpit. An extra nipple (supernumerary nipple) can also develop anywhere along the milk line in both women and men, as can a complete auxiliary breast.

Picture of the milk lines

Rarely, the breast may be absent. The normal growth of the breast or nipple never takes place and there is no sign whatsoever of the breast tissue, areola or nipple.

Absence of the breast (also called amastia) frequently does not occur as the only physical problem. Unilateral amastia (amastia just on one side) is often associated with absence of the pectoral muscles (the muscles of the front of the chest). Bilateral amastia (with absence of both breasts) is associated in 40% of cases with multiple congenital anomalies (birth defects) involving other parts of the body as well.

Amastia can be distinguished from amazia -- wherein breast tissue is absent, but the nipple is present -- a condition that typically is a result of radiation or surgery.

When a woman or a man detects a breast lump, breast cancer is likely the greatest health concern. While many breast lumps are harmless (benign), every breast lump should be evaluated by a doctor to exclude or establish a diagnosis of cancer.

Breast cancer is the most common cancer in women and the second most common cause of cancer death in women in the U.S. One in every eight women in the United States develops breast cancer. The risk is even higher for women:

• with previous breast cancer,
• those who have first-degree relatives with breast cancer,
• those with multiple family members with cancer, and
• those who have inherited "cancer genes."

When detected early, breast cancer has a high cure rate, so the most important strategy in improving survival is breast cancer screening of women with regular mammograms.

In addition to cancers, a number of benign tumors and processes can also affect the breast to cause a lump. Fibroadenoma is an example of a common benign tumor of the breast that occurs in young women. Fibroadenoma is completely cured by surgical removal. Other benign processes in the breast include fibrocystic changes and presence of benign cysts.

Infections of the breast, known as mastitis, are particularly common in women who are breastfeeding. When the skin of the nipple (areola) is injured or cracked, such as occurs with nursing, bacteria can enter the wound and cause infections. Infections can either be a deep pocket of pus, in which the infection looks like it is growing down into the breast (an abscess), or a wider area of skin redness that spreads out (cellulitis).

Cosmetic surgeries are sometimes performed when women request breast reduction or breast augmentation. Although different techniques are used, breast implants have been used for surgical breast enlargement. Breast reconstruction is a cosmetic technique that is also commonly performed after surgical breast removal (mastectomy) for breast cancer.