Lymphatic System

Ready for a trivia question?

Which of these is the result of a parasitic infection of the lymphatic system that causes enormous swelling of the legs and scrotum?

  • A. Hypertrichosis
  • B. Cotard’s Syndrome
  • C. Elephantiasis
  • D. Wolf-Parkinson-White Syndrome

Drum roll please…..

If you answered C, congratulations! If you answered A, B, or D, keep reading.

The lymphatic system is responsible for absorbing excess interstitial fluid and transporting this fluid, called lymph, to ducts that drain into veins. The lymphatic system is also responsible for producing lymphocytes, which are the white blood cells involved in immunity.

The lymphatic system has three main roles: to transport interstitial fluid originally from blood filtrate back to the blood, to transport absorbed fat from the small intestine to the blood, and to provide immunological defense against pathogens.

As blood circulates throughout the body supplying oxygen to tissues, some fluid leaks from the blood into the surrounding tissues (interstitial fluid is formed by filtration of plasma out of blood capillaries). This leakage helps maintain an efficient movement of nutrients and salts from blood into the tissues. Because more than 3 liters of fluid leak from the circulatory system into tissues every day, some of that fluid must return to the circulatory system, otherwise a person would swell up like a balloon. Fortunately, the lymphatic system exists to remove excess fluid from our tissues.

Once fluid collects in lymphatic capillaries, it is referred to as lymph. Lymphatic capillaries are microscopic close-ended tubes that form immense networks in the intercellular spaces within most organs. These capillaries have porous junctions, therefore allowing interstitial fluid, proteins, extravasated white blood cells, microorganisms, absorbed fat, and fat-soluble vitamins to enter. The lymph is carried into larger lymph vessels called lymph ducts. Lymph ducts are similar to veins in that they contain valves to prevent backflow. The lymph moves via peristaltic waves of contraction throughout the lymph vessels until the lymph empties into either the thoracic duct or the right lymphatic duct. These ducts drain into the left and right subclavian veins, respectively. Thus, interstitial fluid is ultimately returned to the cardiovascular system.

Lymph nodes help remove pathogens from the lymph before it enters the circulatory system. Lymph nodes contain phagocytic cells which act as filters, trapping bacteria and other microorganisms that cause disease. If you have had “swollen glands”, then your lymph nodes were swollen in your neck, helping trap and destroy bacteria and other pathogens. The tonsils, thymus, and spleen—the lymphoid organs—are all sites of lymphocyte production. Certain lymphocytes, called T cells, mature in the thymus before they function in the immune system. T cells respond to antigens, which provoke an immune response from one’s body. Although the lymphatic system transports lymphocytes for immune protection, it may also transport cancer cells through the porous lymphatic capillaries, thereby helping cancer metastasize.

Now, finally to explain our trivia question… Lymphedema is excessive protein and associated fluid in the interstitial tissue, caused by inadequate lymphatic drainage. In tropical equatorial regions in the world, most commonly in Africa, a parasitic infection of the lymphatic system causes elephantiasis. Elephantiasis is a lymphedema that produces massive swelling of the legs and scrotum. The skin develops a rough appearance and usually darkens. Lymph flow also becomes obstructed. This disease is caused by a species of nematode worms, and is transmitted by mosquitoes. Chemotherapy, antibiotics, and lymphatic massage have all proven to be helpful treatments.

Take a look at this video about the lymphatic system!


Fox, Stuart I. “Blood, Heart, and Circulation.” Human Physiology. 10th ed. New York, NY: McGraw-Hill, 2008. 424-25. Print.

Levine, Miller. “Circulatory and Respiratory Systems.” Biology. Boston, Massachusetts: Pearson Prentice Hall, 2008. 954-55. Print.

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Written by Rob Nelson

Rob is an ecologist from the University of Hawaii. He is the co-creator and director of Untamed Science. His goal is to create videos and content that are entertaining, accurate, and educational. When he's not making science content, he races whitewater kayaks and works on Stone Age Man.

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