What is lymph? Is it part of the circulatory system in our bodies?

The fluid called lymph is part of the lymphatic system, together with lymphatic vessels, lymph nodes, the thymus, and the spleen. This system is a crucial support to the immune system and also supplements the cardiovascular system by helping to remove toxins from the body. The lymphatic system works in the following ways:
  • The lymphatic system collects excess fluids and plasma proteins from surrounding tissues and returns them to the blood circulation. Within lymphatic vessels, this collected material forms a usually colorless fluid called lymph, which is transported to the neck, where it empties into the circulatory system.
  • The lymphatic system absorbs lipids and fat-soluble materials from the digestive tract.
  • The lymphatic system filters the lymph by destroying pathogens, inactivating toxins, and removing particulate matter. Lymph nodes, small bodies interspersed along lymphatic vessels, act as cleaning filters and as immune response centers that defend against infection.

The movement of lymph through lymphatic vessels is slow (3 liters/day) compared to blood flow (about 5 liters/minute). Lymph does not circulate like blood, but moves in one direction from its collection in tissues to its return in the blood. There are no lymphatic pumps. Instead, lymph, much like blood in veins, is propelled forward by action of the nearby skeletal muscles, the expansion and contraction of the lungs, and the contraction of the smooth muscle fibers in the walls of the lymphatic vessels. Valves in the lymphatic vessels prevent the backward movement of lymph.