The lymphatic system is part of the circulatory system, comprising a network of lymphatic vessels that carry a clear fluid called lymph directionally towards the heart. Unlike the cardiovascular system the lymphatic system is not a closed system. The circulatory system processes an average of 20 litres of blood per day through capillary filtration which removes plasma while leaving the blood cells. Roughly 17 litres of the filtered plasma get reabsorbed directly into the blood vessels, while the remaining 3 litres are left behind in the interstitial fluid. One of the main functions of the lymph system is to provide an accessory route for these excess 3 litres per day to get returned to the blood.
The lymphatic system has multiple interrelated functions:
It is responsible for the removal of interstitial fluid from tissues
It absorbs and transports fatty acids and fats as chyle from the digestive system
It transports white blood cells to and from the lymph nodes into the bones
The lymph transports antigen-presenting cells (APCs), such as dendritic cells, to the lymph nodes where an immune response is stimulated.