The lymphatic system is parallel to the cardiovascular system. This means that it is part of the vascular system and crucial to the immune system. Composed of lymphatic vessels, it is a network that functions to carry a clear fluid known as lymph toward the heart. It is a unique one-way system that eliminates toxic by-products through the end organs such as through the liver, colon, lungs, skin, and kidneys.
The lymphatic system was first described by Olaus Rudbeck and Thomas Bartholin in the seventeenth century. It is not a closed system. The lymphatic system consists of organs that contain lymphoid tissue, vessels that transport lymph, and fluids known as lymph.
While the human circulatory system is a closed system that processes an average of 20 liters of blood per day, about 17 liters is reabsorbed with the 3 remaining liters in the interstitial fluid. This means that one of the main functions of the lymphatic system is to provide a return route for the surplus 3 liters. Other functions include absorption of fat-soluble vitamins and fats from the digestive system and transportation of these components to the venous circulation. Another crucial function of the lymphatic system is serving as defense against other invading organisms. This is performed by the lymph nodes, spleen, and thymus. The lymphoid tissue are the main sites of lymphocyte production.