What is the main function of the lymphatic system?

The primary function of the lymphatic system is to return excess interstitial fluid to the bloodstream and play a crucial role in the body’s immune response. This system collects excess fluid that leaks from blood vessels into surrounding tissues and transports it as lymph back into the circulatory system, preventing edema and maintaining fluid balance in the body.

In addition to fluid balance, the lymphatic system is a key component of the immune system. It houses lymph nodes and lymphoid organs that produce and store immune cells, such as lymphocytes, which help defend the body against pathogens like bacteria and viruses. By facilitating the movement of lymph, the system helps to filter out harmful substances and mobilize immune responses when needed.

Other choices describe functions related to different bodily systems. For instance, filtering blood is primarily managed by the kidneys and spleen, while gas transport is a function of the respiratory and circulatory systems. The digestive system is responsible for breaking down and absorbing food, which does not pertain to the lymphatic system's key functions. Thus, the correct answer captures the essential roles of the lymphatic system in maintaining homeostasis and supporting immunity.