Final answer:
Lymph is the term for the overflow circulatory fluid in spaces between tissues, which is eventually returned to the bloodstream by the lymphatic system after filtration.
Step-by-step explanation:
The overflow circulatory fluid in spaces between tissues is called Lymph. This fluid originates as plasma that leaks out of capillaries into the spaces between cells due to capillary filtration. In humans, around 20 liters of plasma filter into the interstitial space each day, and of this, 17 liters are directly reabsorbed by the blood vessels. The remaining 3 liters, which are not directly reabsorbed, enter the lymphatic system.
The lymphatic system then drains this excess fluid, now called lymph, and returns it to the bloodstream. Lymph is similar in composition to interstitial fluid, except that it has passed through the lymphatic vessels and nodes, where it is filtered - removing infectious agents and debris from the fluid. It ultimately rejoins the circulatory system and contributes to maintaining fluid balance in the body.