Where does interstitial fluid drain?

The correct answer is that interstitial fluid drains into the lymphatic system. Interstitial fluid, which is the fluid that fills the spaces between cells in tissues, plays an important role in maintaining a balance of fluid within the body. While a small portion of interstitial fluid can enter the bloodstream through capillaries, the primary route for drainage of this fluid is through the lymphatic system.

The lymphatic system is a vital component of the immune system and helps to transport excess interstitial fluid back to the circulatory system, preventing fluid accumulation in tissues and maintaining overall fluid balance. This system collects interstitial fluid, which is then termed lymph, and carries it through a network of lymphatic vessels where it eventually re-enters the bloodstream at the thoracic duct.

While other options, such as the kidneys and digestive system, are involved in other functions such as waste removal and absorption of nutrients, they do not directly participate in the drainage of interstitial fluid. Thus, the most accurate response to the question is that interstitial fluid primarily drains into the lymphatic system.