What is the primary role of the lymphatic system in maintaining fluid balance within the body?

The lymphatic system plays a crucial role in maintaining fluid balance in the body by collecting and returning excess interstitial fluid to the bloodstream. Interstitial fluid, which is the fluid that surrounds cells, can accumulate in tissues, leading to swelling or edema. The lymphatic system captures this excess fluid through lymphatic capillaries, which are highly permeable and can take up larger molecules and particulate matter that the blood capillaries cannot. Once collected, lymph travels through lymphatic vessels and eventually returns to the circulatory system at the junction of the subclavian veins.

This process ensures that the fluid levels in tissues remain balanced, preventing both dehydration (due to excessive fluid loss) and overhydration (due to fluid retention). While the other options describe important functions of different systems (like oxygen transport, nutrient absorption, and toxin filtration), they do not encompass the primary function of the lymphatic system, which centers around fluid balance and homeostasis.