Lymph
The blood plasma-like fluid, which escapes from the capillaries into the extracellular space, fills the interstitial extracellular spaces depending on arterial and venous blood pressure, tissue pressure and colloidosmotic pressure.
It is partly collected by the blind ending lymph capillaries of the lymph vessel system and is derived with the support of the muscle pump. Larger lymphatic vessels and lymph nodes have valves to prevent reverse flow. As it flows through the lymph nodes, the lymph absorbs abundantly lymphocytes. The lymph vessels unite in the thoracic duct, which opens into the upper vena cava before the heart.