Which term refers to the bodily network described as lining the body with fluid-filled tissues and a substantial portion of body fluids?

• A. Interstitium
• B. Endothelium
• C. Peritoneum
• D. Cartilage

Answer: (A)

Interstitium is the network of fluid-filled spaces that permeate most tissues and surround individual cells. It contains interstitial fluid, which forms a large portion of the body's extracellular fluids. This expansive, fluid-filled network is the medium through which nutrients, gases, and waste diffuse between blood vessels and cells, effectively lining the body with fluid-filled tissues. The other options describe specific surfaces or tissues: endothelium lines the inner surfaces of blood and lymphatic vessels, peritoneum lines the abdominal cavity, and cartilage is a dense, supportive tissue, not a widespread fluid-filled network.