Which system is described as a network of fluid-filled tissues that line the body and relates to a fifth of body fluids?

• A. Interstitium
• B. Endocrine System
• C. Lymphatic System
• D. Digestive System

Answer: (A)

The interstitium is the network of fluid-filled spaces between cells in our tissues. It forms part of the extracellular fluid and acts as the bath that surrounds cells, carrying nutrients to them and taking waste away. This interstitial fluid accounts for about a fifth of the body’s fluids, which matches the description of a network of fluid-filled tissues lining the body. It’s distinct from systems like the endocrine (hormones), lymphatic (drainage vessels), or digestive (breaking down food) systems. The key idea is that the interstitium is the cellular surroundings—fluid-filled spaces that lie between cells throughout the body.