Answer
Substances cross capillary walls through intercellular clefts and fenestrations, by transcytosis, and through plasma membranes of endothelial cells.
Work Step by Step
The ultimate function of the cardiovascular system is to facilitate capillary exchange, that is, the movement of substances between the blood and the interstitial fluid(ISF). Substances enter and leave the blood mainly in three ways-- diffusion, transcytosis, and bulk flow.