Which system is responsible for returning excess interstitial fluid to the blood and protecting the body against disease?

The lymphatic system is responsible for returning excess interstitial fluid to the blood and plays a critical role in the immune system by protecting the body against disease. Interstitial fluid, which is the fluid that fills the spaces between cells, can accumulate in tissues if not properly drained. The lymphatic system collects this excess fluid, known as lymph, and transports it back to the bloodstream, thus maintaining fluid balance within the body.

Additionally, the lymphatic system includes lymph nodes and lymphoid organs, which are crucial in filtering the lymph and trapping pathogens, thus supporting the immune response. This system helps the body identify and fight off infections and other diseases, making it an essential component of both fluid management and immune defense.

In contrast, while the circulatory system also transports fluids and plays a role in immune responses, it does not specifically handle the drainage and return of interstitial fluid in the way the lymphatic system does. The respiratory system is primarily involved in gas exchange, and the nervous system is responsible for transmitting signals throughout the body to coordinate various functions, neither of which directly concern the return of interstitial fluid or disease protection.