Each breast has 15 to 20 sections, or lobes, that surround the nipple, like spokes on a wheel. Inside these lobes are smaller lobes, called lobules. At the end of each lobule are tiny "bulbs" that produce milk. These structures are linked together by small tubes called ducts, which carry milk to the nipples. The nipple is in the center of a dark area of skin called the areola. The areola contains small glands that lubricate the nipple during breastfeeding. Fat fills the spaces between the lobes and ducts. There are no muscles in the breasts, but muscles lie under each breast and cover the ribs.
Each breast also contains blood vessels and vessels that transport lymph. Lymph is a fluid that travels through the lymphatic system and carries cells that help the body fight infections. The lymph vessels lead to the lymph nodes (small, bean-shaped glands that are part of the infection-fighting lymphatic system). A group of lymph nodes are located in the armpits, above the collarbone, and in the chest. If the cancer has reached these nodes, it may mean that cancer cells have spread to other parts of the body.
Lymph nodes are also found in many other parts of the body.
Breast development and function depend on the hormones estrogen and progesterone, which are produced in the ovaries. Estrogen elongates the ducts and causes them to create side branches. Progesterone increases the number and size of the lobules in order to prepare the breast for nourishing a baby. After ovulation, progesterone makes the breast cells grow, and blood vessels enlarge and fill with blood. At this time, the breasts often become engorged with fluid and may be tender and swollen.
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 2/23/2009...#8330