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The lymphatic system is a network that runs throughout the human body, which has a number of different functions. Serving as one of the body’s main vessels of immunity, the lymphatic's primary function is to create immune cells. The system also helps to shuttle away fluids from tissue in the body, as well as absorb fat and move that fat to the circulatory system.
It is easiest to think of the lymphatic system as being, in many ways, analogous to the circulatory system. Both are extensive networks of tubes that go virtually everywhere in the body. But where the circulatory system moves blood around the body, the lymphatic system moves a clear liquid known as lymph throughout the body.
Lymph is full of white blood cells, also known as lymphocytes, which are the body’s main tools in the immune response. When plasma is released into tissue to help the body, the lymph vessels are where it ultimately drains, so that they can transport it away from the tissue to the thoracic duct, where it is returned to the circulatory system.
At a point along the body within the lymphatic system there are small nodes, known as lymph nodes. These lymph nodes are full of white blood cells, and act as vessels to filter out foreign matter. When the body fights off sickness, the white blood cell count increases dramatically to help battle the virus or bacteria, and the white blood cells collect in the lymph nodes. This is why the lymph nodes may swell when a person has an infection. There are hundreds of lymph nodes found throughout the human body, but they tend to be found in large clusters in the groin, chest, neck, abdomen, and armpits.
Unlike the heart for the circulatory system, the lymphatic system isn’t pressurized by a muscle and therefore lymph doesn’t flow at nearly the same speed. Instead, the flow of lymph through the system is fairly slow, driven by small valves, and the slight contraction of muscles around the skeleton. Because the pressure involved is so slight, it is actually fairly easy to hamper the flow of lymph throughout the body. Since the results are not nearly as drastic as, for example, hampering the flow of blood would be, many people do not immediately notice a change. Even wearing very tight clothing for long periods of time can slow down the functioning of the lymphatic system, resulting in the fluid buildup usually referred to as edema.
There are a number of various medical conditions in which the lymphatic system is either hampered or is acting incorrectly. Lymphoma is perhaps the most well-known of these conditions, in which the system becomes cancerous. Lymphedema is also fairly common, with nearly 200 million people suffering from it worldwide. Lymphedema is usually caused either by an inherited condition, or by some sort of trauma to lymph nodes, such as after radiation therapy or surgery. Fluid begins to accumulate in an area, the skin may discolor, and limbs may become extremely heavy and full of fluid. If left untreated, lymphedema can become elephantiasis, where the skin thickens greatly and limbs or localized regions of the body become incredibly swollen.