The lymphatic system consists of a network of hollow tubes that carry a protein-rich fluid called lymph. This system also includes lymph nodes, clusters of immune system cells that protect the body from infections. In addition to its protective role, the lymphatic system is essential for returning vital proteins and fluid to the bloodstream. Many types of diseases can affect the lymphatic system, but obstructive conditions, infections and cancer are the most common. Rarely, structural or functional problems may arise.
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Swelling and Lymphedema
Approximately 2 to 4 liters of lymph circulate through the lymphatic system daily. When the lymphatic vessels are cut, scarred, blocked or destroyed, fluid accumulates in the nearby tissues and causes swelling. This condition is termed lymphedema. Common destructive causes include surgery, especially if lymph nodes are removed, and radiation treatment for cancer. Poor venous circulation -- which may occur during late pregnancy -- and immobility due to disease or obesity can also lead to lymphedema.
Lymphadenitis and Lymphangitis
When germs enter the body, they are commonly picked up by the lymphatic system. They often then infect nearby lymph nodes, causing enlargement and tenderness. The medical term for this condition is lymphadenitis, but it is more commonly known as "swollen glands." Many common bacterial and viral infections can cause swollen glands, which go back to normal after the infection clears. The lymphatic vessels can also become infected and inflamed, a condition known as lymphangitis. Red streaks appear on the skin along the route of the inflamed lymphatic vessels, typically accompanied by fever and chills. Streptococcal bacteria are the most common cause of lymphangitis.
Spread of Cancer
Lymphoma is a type of cancer involving immune cells of the lymphatic system known as lymphocytes. This cancer can arise anywhere in the body and is broadly divided into Hodgkin and non-Hodgkin lymphoma types. Lymphangiosarcoma is a rare from of cancer that sometimes develops in people who have had lymphedema for many years. Cancers that start outside the lymphatic system -- such as breast, lung and colon cancers -- also frequently spread to the lymph nodes. This type of cancerous invasion of the lymph nodes is called lymph node metastasis.
The lymphatic vessels sometimes form incorrectly or grow abnormally. For example, a lymphangioma is a noncancerous, lymph-filled growth that arises when small lymphatic vessels do not connect normally with the rest of the lymphatic system. These growths are most commonly seen during infancy and childhood, but adults can also be affected. Lymphangiectasia is another type of structural abnormality of the lymph system that occurs when the lymphatic vessels become damaged and lymph backs up. The affected vessel expands like a balloon, causing a noncancerous growth, which may leak lymph fluid. People with this condition also commonly have lymphedema.
Lymph nodes can be found throughout the body but are most heavily concentrated in areas vulnerable to infection. Each lymph node houses large numbers of infection-fighting cells called lymphocytes. When the lymphocytes do not function properly -- a condition broadly known as an immunodeficiency -- even a minor illness like a cold may become life-threatening. Primary immunodeficiency disorders are inherited and present at birth. Others that develop later in life are called secondary immunodeficiencies, such as the human immunodeficiency virus/AIDS.