Final answer:
It is necessary to return leaked-out fluid to maintain fluid balance and prevent medical issues like lymphedema. The lymphatic system collects excess interstitial fluid, filters it, and returns the cleansed fluid to the bloodstream.
Step-by-step explanation:
The necessity to return leaked-out fluid to the bloodstream is crucial for maintaining bodily functions. When blood pressure forces plasma to leak from the capillaries into the interstitial space, most of this fluid is reabsorbed directly by the blood vessels. However, approximately 3 out of 20 liters daily are not reabsorbed and must be returned to the circulation through the lymphatic system to prevent fluid imbalance. The lymphatic system collects this interstitial fluid, now termed lymph, and after filtering it through lymph nodes, it returns the cleansed lymph back to the bloodstream. This process is essential for maintaining fluid balance, preventing lymphedema, and supporting the immune system by removing infectious agents and debris from the fluid.