Large molecules in colloid solutions remain in which space?

• A. Intracellular space
• B. Vascular space
• C. Interstitial space
• D. Lymphatic space

Answer: (B)

Large molecules in colloid solutions stay in the intravascular (vascular) space because capillary walls selectively restrict their movement. The endothelium allows water and small solutes to pass, but big proteins are too large to cross, so they remain confined to the blood vessels. This is the basis for how colloid expanders work: they raise oncotic pressure and draw fluid from the interstitial space back into the bloodstream, keeping the large molecules inside the vascular compartment.