The Lymphatic System
The lymphatic system is an extensive drainage network that helps keep bodily fluid levels in balance and defends the body against infections. It is made up of a complex network of lymphoid organs, lymph nodes, lymph ducts, lymph tissues, lymph capillaries and a network of lymphatic vessels that carry lymph and other substances throughout the body.
In comparison to the cardiovascular system the lymphatic system has not in the past been the focus of much research. However its' important role in the body's immune system has meant that it has increasingly become the focus of research in more recent times.
The spleen, which is located in the upper left part of the abdomen under the ribcage, works as part of the lymphatic system to protect the body, clearing worn out red blood cells and other foreign bodies from the bloodstream to help fight off infection.
The lymphatic system has three functions:
- The removal of excess fluids from body tissues. This process is crucial because water, proteins, and other substances are continuously leaking out of tiny blood capillaries into the surrounding body tissues. If the lymphatic system didn't drain the excess fluid from the tissues, the lymph fluid would build up in the body's tissues, and they would swell.
- Absorption of fatty acids and subsequent transport of fat, chyle, to the circulatory system.
- Production of immune cells (such as lymphocytes, monocytes, and antibody producing cells called plasma cells).
Fluid and Protein Balance
As blood moves through the arteries and veins, 10% of the fluid filtered by the capillaries, along with vital proteins, becomes trapped in the tissues of the body. This loss of this fluid (approximately 1-2 liters/day) would rapidly become life threatening if the lymphatic system did not properly function. The lymphatic system collects this fluid and returns it to the circulatory system.
Immunity and Spread of Infection
The lymphatic system plays an integral role in the immune functions of the body. It is the first line of defense against disease. This network of vessels and nodes transports and filters lymph fluid containing antibodies and lymphocytes (good) and bacteria (bad). The body's first contact with these invaders signals the lymphatics, calling upon this system to orchestrate the way the infection-fighting cells prevent illness and diseases from invading microorganisms. The spleen also helps the body fight infection. The spleen contains lymphocytes and another kind of white blood cell called macrophages, which engulf and destroy bacteria, dead tissue, and foreign matter and remove them from the blood passing through the spleen.
Lymph vessels in the lining of the gastrointestinal tract absorb fats from food. A malfunction of this part of the lymphatic system can result in serious malnutrition. The lymphatic system also impacts diseases such as excessive obesity caused by abnormal fat and carbohydrate metabolism.
The lymphatic system is a network of very small tubes (or vessels) that drain lymph fluid from all over the body. The major parts of the lymph tissue are located in the bone marrow, spleen, thymus gland, lymph nodes, and the tonsils. The heart, lungs, intestines, liver, and skin also contain lymphatic tissue.
One of the major lymphatic vessels is the thoracic duct, which begins near the lower part of the spine and collects lymph from the pelvis, abdomen, and lower chest. The thoracic duct runs up through the chest and empties into the blood through a large vein near the left side of the neck. The right lymphatic duct is the other major lymphatic vessel and collects lymph from the right side of the neck, chest, and arm, and empties into a large vein near the right side of the neck.
Lymph nodes are round or kidney-shaped, and can be up to 1 inch in diameter. Most of the lymph nodes are found in clusters in the neck, armpit, and groin area. Nodes are also located along the lymphatic pathways in the chest, abdomen, and pelvis, where they filter the blood. Inside the lymph nodes, lymphocytes called T-cells and B-cells help the body fight infection. Lymphatic tissue is also scattered throughout the body in different major organs and in and around the gastrointestinal tract.
How a Healthy Lymph System Typically Works
Carrying Away Waste
Lymph fluid drains into lymph capillaries, which are tiny vessels. The fluid is then pushed along when a person breathes or the muscles contract. The lymph capillaries are very thin, and they have many tiny openings that allow gases, water, and nutrients to pass through to the surrounding cells, nourishing them and taking away waste products. When lymph fluid leaks through in this way it is called interstitial fluid. Lymph vessels collect the interstitial fluid and then return it to the bloodstream by emptying it into large veins in the upper chest, near the neck.
Lymph fluid enters the lymph nodes, where macrophages fight off foreign bodies like bacteria, removing them from the bloodstream. After these substances have been filtered out, the lymph fluid leaves the lymph nodes and returns to the veins, where it re-enters the bloodstream.
Looking at the Lymphatic System
Lymphatic vessels and lymph nodes can be visualized by the process of lymphangiography. A radiopaque (not transparent to x-rays) contrast material is injected into a lymphatic vessel. This will show up the vessel and its' connections to other lymph vessels. The fluid is left in the system for 24 hours and the lymph nodes can then be observed by X-rays. This technique is quite important in the treatment of neoplasms and other disorders of the lymphatic system. The technique is also used to locate lymph nodes for radiation therapy or for surgical removal.
*From The Merck Manual of Medical Information – Second Home Edition, p. 1053, edited by Mark H. Beers. Copyright 2003 by Merck & Co., Inc., Whitehouse Station, NJ. Available at:http://www.merck.com/mmhe Accessed (April 25, 2008).
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