Final answer:
Sappey's line is associated with the lymphatic drainage system, which functions to absorb excess interstitial fluid and return it to the blood circulation.
Step-by-step explanation:
Sappey's line is associated with lymphatic drainage. The lymphatic system, which includes lymphatic vessels and capillaries, is responsible for the collection and transport of interstitial fluid, which is the fluid found between cells. This system plays a vital role in maintaining fluid balance within the body by absorbing excess fluid and returning it to the bloodstream through the lymph nodes and lymph ducts.