What is the primary function of the lymphatic system?

• A. To transport blood throughout the body
• B. To filter the blood in the kidneys
• C. To transport lymph, a fluid containing infection-fighting white blood cells, throughout the body
• D. To regulate body temperature

Answer: (C)

The lymphatic system’s main job is to move lymph, a fluid that bathes tissues and carries immune cells, through the body. Lymph forms from interstitial fluid and travels via lymph vessels toward the bloodstream. Along the way, lymph passes through lymph nodes where pathogens are filtered and immune responses can be activated. This system helps maintain fluid balance and supports the body’s defense against infection, which is why the description of transporting lymph containing infection-fighting white blood cells best captures its primary function.

The other ideas fit different body systems: transporting blood is the job of the cardiovascular system, filtering blood in the kidneys is the renal/urinary system, and regulating body temperature involves the skin, nerves, and circulatory responses rather than the lymphatic pathway.