Layered over top of the chest muscles, the breast can cover a fairly large area. Breast tissue extends from just below your collarbone (clavicle), to your armpit (axilla) and across to your sternum. The breast itself is a specially designed mass of glandular, fatty, and connective tissues known in medical terms as a "mammary gland".
The breast is made up of 6 distinct elements:
- Lobules are the glands that are responsible for producing milk. They resemble bunches of grapes and most adult women have around 15 to 20 in each breast.
- Ducts are small tubes that carry the milk to the nipple.
- Fatty and connective tissue surround the lobules and ducts to protect them while giving shape, size, and structure to the breast.
- The areola is the circle of darker skin around the nipple. It has small sweat glands that help during breastfeeding.
- The nipple is, of course, at the centre of the areola and is where the milk comes out.
- There are ligaments that run from the skin through the breast tissue. They attach to the pectoral muscles in the chest to provide support.
The Lymphatic System
The lymphatic system is a major offshoot of your circulatory system and plays a critical role in your body's ability to fight disease and infection. Lymph vessels are small, tube-like structures very similar to blood vessels. However, instead of transporting blood they collect and move a clear liquid called “lymph”. Lymph fluid is moved away from organs, in this case the breasts, into the lymph nodes, which are shaped like little beans. The nodes filter infections and toxins and distribute white blood cells where they are needed. This system is specialized further in your breasts, with four distinct types of breast lymph nodes:
- Supraclavicular nodes are above the collarbone.
- Infraclavicular, or subclavicular nodes are located below the collarbone.
- Internal mammary nodes are found inside the chest among the breast tissue and around the sternum.
- Axillary nodes are in the armpit.
Axillary lymph nodes are the most prevalent, with about 30 to 50 in and around each armpit. The exact number differs between women. These lymph nodes can be divided into three levels based on how close to the chest muscle they are:
Level I , or low axilla nodes are found in the bottom part of the armpit, running along the outside edge of the chest muscle.
- Level II , or mid axilla nodes are located a bit higher than level I, in the middle section of the armpit beneath the chest muscle.
- Level III , or high axilla nodes are the highest group axillary nodes, found just below and near the centre of the collarbone. These nodes are higher than the actual breast tissue and run along the inside edge of the chest muscle.
(In the event of breast cancer, it tends to spread to the level I lymph nodes first, before moving to level II and then level III.)
The tissue in your breasts will go through some changes throughout the normal course of your life. The first major change occurs during puberty, but breast tissue also changes during your menstrual cycle, pregnancy, and after menopause.
Prior to puberty, female and male breast tissue aren't all that different from one another. This changes during puberty when female breast tissue begins to develop as it responds to normal increases in estrogen and progesterone in the body. It is during this awkward and uncomfortable phase of life that the breast ducts and milk glands grow. While all breasts are made of both glandular tissue and fatty tissue, younger women tend to have more glandular tissue, which means they have denser breasts. In older women, the glandular tissue of the lobules is replaced with more fatty tissue, making their breasts less dense.
Breast tissue also goes through a monthly change as a part of the normal menstrual cycle. During the first part of the menstrual cycle, the estrogen your body produces is carried to your breasts through your blood and encourages the milk ducts to grow and open. In the second part of your cycle progesterone takes over and stimulates the lobules to begin producing milk. After menopause this monthly cycle stops, but estrogen continues to be made in other parts of your body.
Some women have a lot of breast tissue, and thus have larger breasts, while other women have less tissue resulting in smaller breasts. But regardless of the amount of fatty tissue and the size of the breast, when it comes to healthy milk production, size is irrelevant.