Breast facts:
- The breasts are medically known as the mammary glands.
- The mammary glands are made up of lobules, milk-producing glandular structures, and a system of ducts that transport milk.
- Lymphatic vessels in the breast drain excess fluid.
- Breast growth begins at puberty in humans, in contrast to other types of primates in which breasts enlarge only during lactation.
- Breast tissue develops in the fetus along the so-called "milk lines," extending from the armpit to the groin.
What are the breasts (mammary glands)?
The breasts, located on the front of the chest, are medically known as the mammary glands. The term "breast" is sometimes used to refer to the area at the front of the chest.
What are the anatomical features of the breast?
The mammary gland is made up of lobules, glandular structures that produce milk in females when stimulated to do so. The lobules drain into a system of ducts, connecting channels that transport the milk to the nipple. Between the glandular tissue and ducts, the breast contains fat tissue and connective tissue.
Both males and females have breasts; the structure of the male breast is nearly identical to that of the female breast, except that the male breast tissue lacks the specialized lobules, as there is no physiologic need for milk production by the male breast. Abnormal enlargement of the male breasts is medically known as gynecomastia.
The breast does not contain muscles. Breast tissue is located on top of the muscles of the chest wall. Blood vessels and lymphatic vessels (a system of vessels that drains fluid) are located throughout the breast. The lymphatic vessels in the breast drain to the lymph nodes in the underarm area (axilla) and behind the breast bone (sternum).
In females, milk exits the breast at the nipple, which is surrounded by a darkened area of skin called the areola. The areola contains small, modified sweat glands known as Montgomery's glands. These glands secrete fluid that serves to lubricate the nipple during breastfeeding.
What happens to the breasts in pregnancy?
During pregnancy, the breasts grow further due to stimulation by estrogens (female hormones). The growth during pregnancy is more uniform than that observed at puberty. The amount of tissue capable of producing milk is approximately the same in all women, so women with smaller breasts produce the same amount of milk as women with larger breasts. During pregnancy, the areola becomes darker and enlarges in size.
How does breast tissue develop?
Breast tissue begins to form in the fourth week of fetal life. In the fetus, breast tissue develops along two "milk lines" that start at the armpit and extend to the groin. Uncommonly, an extra (ancillary) breast can develop along this line. On the skin surface, an extra nipple (supernumerary nipple) may develop along this line.
How are human breasts different from other species?
In other primates (such as apes), the breasts develop only when they are producing milk. After the young have been weaned, the breasts flatten again. In humans, the breasts enlarge at puberty and stay enlarged throughout a woman's life.
What are the most common medical conditions affecting the breasts?
Breast health is a source of concern for most women. Although breast cancer is a fairly common malignancy affecting one out of every eight women in the U.S. at some point in life, benign (non-cancerous) conditions of the breast are much more common. In fact, most masses and lumps in the breasts are not cancer. Breast cancer occurs in males as well, but it accounts for a small percentage of all breast cancers.
Among the benign breast conditions, cysts and fibrocystic changes are common. One type of benign tumor in particular, known as a fibroadenoma, is common in young women. Infections of the breast tissue can also occur, particularly during breastfeeding. Mastitis is the medical term for inflammation of the breast.