Capillary blood is composed of interstitial fluid, intracellular fluids, and arterial and venous blood. Which option expresses this statement as true?

• A. True
• B. False
• C. Only interstitial fluid
• D. Only arterial blood

Answer: (A)

Capillary blood is the blood that flows through the small vessels, consisting of plasma and formed elements (red cells, white cells, platelets) moving within the vessels. Interstitial fluid is the extracellular fluid that surrounds tissue cells outside the capillaries, and intracellular fluid is the fluid contained inside the cells. These are separate compartments. While capillary exchange allows water and solutes to move between plasma and the surrounding interstitial fluid, interstitial fluid itself is not part of capillary blood, and intracellular fluid is not part of blood at all. So the statement blends fluids from different compartments and isn’t accurate, even though capillary plasma can exchange with interstitial fluid.