Substances absorbed by the lymphatic route are partly fat-like substances. For example, a portion of glycerol and fatty acids end up in the blood circulation through the lymphatic circulation. Some other substances, such as inorganic salts, water, amino acids, glucose, and another portion of lipids are absorbed directly into the blood circulatory system. Lymph, also known as lymphatic fluid, is a colorless, transparent fluid in humans and animals that contains lymphocytes and is formed partly by the infiltration of tissue fluid into lymphatic vessels. Lymphatic vessels are tubes similar in structure to veins and are distributed throughout the body. Lymph circulates in the lymphatic vessels and eventually flows into the veins, where some of the tissue fluid flows into the bloodstream and back again. Lymph is found in all parts of the body and has a vital role in the body’s immune system. The lymphatic system is an important defense system in the human body and is found throughout the body. It is composed of lymphatic vessels (divided into capillary lymphatic vessels, lymphatic ducts, lymphatic trunks and lymphatic conduits), lymphatic tissues (divided into diffuse lymphatic tissues and lymphatic nodes), and lymphatic organs (such as the thymus gland, bone marrow, spleen, tonsils, etc.).