What fluid circulates through the lymphatic system?

The fluid that circulates through the lymphatic system is lymph. Lymph is a clear fluid that originates from interstitial fluid, which is the fluid found between cells. Once this interstitial fluid enters the lymphatic vessels, it is called lymph. The primary function of the lymphatic system is to transport lymph throughout the body, helping to remove waste products, excess fluids, and foreign materials, such as pathogens. Lymph also plays a crucial role in the immune system, as it transports lymphocytes and other immune cells.

In contrast, plasma is the liquid component of blood and does not circulate in the lymphatic system; instead, it is part of the circulatory system. Serum is a component of blood that remains after clotting, containing water, electrolytes, antibodies, and other substances, but it is not relevant to the lymphatic system either. Interstitial fluid is the precursor to lymph and is found in the spaces between cells, but once it enters the lymphatic vessels, it becomes lymph, making lymph the correct term for the fluid specifically associated with the lymphatic system.