Final answer:
The lymphatic system provides a one-way route for fluid from the tissue spaces to enter the blood.
Step-by-step explanation:
The fluid that bathes the cells, known as interstitial fluid, is absorbed by tiny lymphatic vessels and forms lymph. This lymph then proceeds to lymph nodes and eventually enters the blood.
In contrast to the closed circulatory system, where blood is present inside blood vessels, in an open circulatory system, the circulatory fluid directly bathes the internal organs. In an open system, there is no separation between blood and interstitial fluid.
In summary, the lymphatic system is responsible for collecting interstitial fluid and returning it to the bloodstream, providing a one-way route for fluid from the tissue spaces to enter the blood.