What is the primary function of the lymphatic system?

The primary function of the lymphatic system is to return excess interstitial fluid to the bloodstream. This function is vital for maintaining fluid balance within the body. The interstitial fluid is the fluid that surrounds the cells in tissues, and it can accumulate if not properly drained. The lymphatic system collects this excess fluid, known as lymph, and it eventually transports this lymph back to the circulatory system, ensuring that the body's tissues do not become swollen or edematous.

Additionally, the lymphatic system plays an important role in immune function, as it transports lymphocytes and other immune cells and filters lymph through lymph nodes. However, its primary and most fundamental role is to manage and return interstitial fluid, which prevents potential complications from fluid overload.

The other options do not accurately describe the primary role of the lymphatic system. While red blood cell production occurs primarily in the bone marrow, filtering blood for pathogens is primarily the job of the spleen and other lymphoid organs rather than the lymphatic system itself. Transporting oxygen to body tissues is a function of the circulatory system and is carried out by red blood cells within the bloodstream.