It is important for women to become familiar with the normal anatomy and physiology (function) of their breasts so that they can recognize early signs of possible abnormalities. This section outlines basic information on breast composition, development, and typical changes from puberty to pregnancy to menopause.
The breast is a mass of glandular, fatty, and fibrous tissues positioned over the pectoral muscles of the chest wall and attached to the chest wall by fibrous strands called Cooper’s ligaments. A layer of fatty tissue surrounds the breast glands and extends throughout the breast. The fatty tissue gives the breast a soft consistency.
The glandular tissues of the breast house the lobules (milk producing glands at the ends of the lobes) and the ducts (milk passages). Toward the nipple, each duct widens to form a sac (ampulla). During lactation, the bulbs on the ends of the lobules produce milk. Once milk is produced, it is transferred through the ducts to the nipple.
The breast is composed of:
milk glands (lobules) that produce milk
ducts that transport milk from the milk glands (lobules) to the nipple
areola (pink or brown pigmented region surrounding the nipple)
connective (fibrous) tissue that surrounds the lobules and ducts
Arteries carry oxygen rich blood from the heart to the chest wall and the breasts and veins take de-oxygenated blood back to the heart. The axillary artery extends from the armpit and supplies the outer half of the breast with blood; the internal mammary artery extends down from neck and supplies the inner portion of the breast.
Initial Breast Development
Human breast tissue begins to develop in the sixth week of fetal life. Breast tissue initially develops along the lines of the armpits and extends to the groin (this is called the milk ridge). By the ninth week of fetal life, it regresses (goes back) to the chest area, leaving two breast buds on the upper half of the chest. In females, columns of cells grow inward from each breast bud, becoming separate sweat glands with ducts leading to the nipple. Both male and female infants have very small breasts and actually experience some nipple discharge during the first few days after birth.
Female breasts do not begin growing until puberty—the period in life when the body undergoes a variety of changes to prepare for reproduction. Puberty usually begins for women around age 10 or 11. After pubic hair begins to grow, the breasts will begin responding to hormonal changes in the body. Specifically, the production of two hormones, estrogen and progesterone, signal the development of the glandular breast tissue. This initial growth of the breast may be somewhat painful for some girls. During this time, fat and fibrous breast tissue becomes more elastic. The breast ducts begin to grow and this growth continues until menstruation begins (typically one to two years after breast development has begun). Menstruation prepares the breasts and ovaries for potential pregnancy.
Breast Size, Appearance, and Changes Over Time
The size and shape of women’s breasts varies considerably. Some women have a large amount of breast tissue, and therefore, have large breasts. Other women have a smaller amount of tissue with little breast fat.
Factors that may influence a woman’s breast size include:
Volume of breast tissue
Weight loss or gain
History of pregnancies and lactation
Thickness and elasticity of the breast skin
Degree of hormonal influences on the breast (particularly estrogen and progesterone)
A woman’s breasts are rarely balanced (symmetrical). Usually, one breast is slightly larger or smaller, higher or lower, or shaped differently than the other. The size and characteristics of the nipple also vary greater from one woman to another. In some women, the nipples are constantly erect. In others, they will only become erect when stimulated by cold or touch. Some women also have inverted (turned in) nipples. Inverted nipples are not a cause for concern unless the condition is a new change. Since there are hair follicles around the nipple, hair on the breast is not uncommon.
The nipple can be flat, round, or cylindrical in shape. The color of the nipple is determined by the thinness and pigmentation of its skin. The nipple and areola (pigmented region surrounding the nipple) contain specialized muscle fibers that respond to stimulation to make the nipple erect. The areola also houses the Montgomery’s gland that may appear as tiny, raised bumps on the surface of the areola. The Montgomery’s gland helps lubricate the areola. When the nipple is stimulated, the muscle fibers will contract, the areola will pucker, and the nipples become hard.
Breast shape and appearance undergo a number of changes as a woman ages. In young women, the breast skin stretches and expands as the breasts grow, creating a rounded appearance. Young women tend to have denser breasts (more glandular tissue) than older women.