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.