What is the primary function of the lymphatic system in maintaining fluid balance and supporting immune defense?

• A. It circulates oxygen and removes carbon dioxide from tissues.
• B. It primarily drains venous blood from tissues.
• C. The lymphatic system transports lymph fluid, filters it through lymph nodes, drains excess interstitial fluid, and supports immune surveillance by filtering pathogens and presenting antigens.
• D. It produces lymphocytes in the spleen only.

Answer: (C)

The lymphatic system keeps two big things in balance: fluid in the tissues and the body’s defense against invaders. It does this by collecting interstitial fluid that leaks out of capillaries, forming lymph, and then returning that fluid to the bloodstream. This drainage prevents swelling and helps maintain circulating blood volume. At the same time, lymph passes through lymph nodes where pathogens are filtered out and immune cells review what’s in the fluid. Antigen-presenting cells expose invaders to lymphocytes, helping to trigger and coordinate immune responses. That combination of draining excess fluid and enabling immune surveillance is what makes this function the best fit.

The other options don’t fit the question’s scope. Circulating oxygen and removing carbon dioxide are duties of the respiratory and cardiovascular systems, not the lymphatic system. Draining venous blood is a venous system function, not the lymphatic drainage of interstitial fluid. Lymphocyte production isn’t limited to the spleen; lymphocytes originate in the bone marrow (with maturation in the thymus for T cells), and the spleen supports immune activity rather than being the sole production site.