Breast Anatomy and Function
Let's review the structure and function of the
breast. Some of the terms like "lymph nodes" and "lobules"
may be new to you, but they will help you
understand breast cancer treatment better.
Although the general shape of a breast is circular or teardrop, breast
tissue can be found from the collarbone to the bra line, and from
the breastbone to the armpit. That is why it is important for you
and your physician to examine that entire area during breast examination.
Breasts are made up of milk-producing glands and milk-carrying ducts,
imbedded in fatty tissue and fibrous supportive tissue. The glands
are grouped in sections, called lobes. Each lobe has many smaller
lobules that end in dozens of tiny grape-like bulbs where milk is
produced. Slender tubes called ducts carry the milk from the lobes
to the nipple. Most of the rest of the breast is composed of fatty
tissue and fibrous supportive tissue.
Two muscles, the pectoralis major and the pectoralis minor, are attached
to the ribs under the breast. One of these muscles may be cut to allow
room for an implant. There are no muscles within the breast itself.
The area of darker skin around the nipple is called the areola.
Arteries and veins carry blood to and from the breast, supplying it
with nutrients and oxygen.
An important concept to understand is the lymphatic system. Lymph
is the fluid that leaks out of the blood vessels and accumulates between
cells. Lymph ducts collect this fluid and return it to the main circulation.
Along the way, lymphatic fluid is filtered through small bean-shaped
structures called lymph nodes, which trap debris such as bacteria,
or escaped cancer cells. You may think of the lymphatic system as
a network of sewer lines.
Most of the lymphatic fluid from the breast drains toward the armpit
area (the axilla), where it is filtered through the axillary lymph
nodes. By examining these nodes, the surgeon can get a good indication
of whether cancer cells have begun to escape from the breast toward
the rest of the body.
From birth to old age, breasts go through more changes than almost
any other organ in the body.
One to two years before menarche (first menstrual period) breasts
begin to grow under the influence of the female hormones estrogen
During reproductive years, variations in the levels of these hormones
cause the breasts to go through monthly cycles: milk glands become
engorged and the breasts swell, as if getting ready for a pregnancy,
then return to their inactive state again.
At menopause, levels of hormones drop, many milk producing glands
shrink and disappear, and some of the breast tissue is replaced with
All these changes sometimes damage the cells' DNA (the genetic material
tells the cell how to divide and grow). This damage may lead to cancer.
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