Final answer:
The assertion regarding large solutes diffusing through endothelial cells or intercellular clefts is true. Facilitated diffusion helps small solutes cross cell membranes through specialized channels, but larger molecules like plasma proteins are transported by vesicular transport rather than by simple diffusion.
Step-by-step explanation:
The statement that large solutes may diffuse via the endothelial cells or intercellular clefts is true. To elucidate, in the body's capillaries, small solutes like gases and lipid-soluble molecules can directly pass through the capillary walls. However, larger substances, including glucose, ions, and certain larger molecules, have to utilize mechanisms such as facilitated diffusion to pass through specific membrane channels.
Moreover, substances like plasma proteins that are suspended in blood do not cross the capillary wall by diffusion; instead, they are transported by vesicular transport including endocytosis and exocytosis. This is because plasma proteins are large and structurally do not function as typical solutes; they are too large to dissolve and instead remain dispersed in the plasma forming a colloid.
In terms of facilitated diffusion, this process allows substances to cross cell membranes with the assistance of protein carriers or channels, without which these substances could not pass freely through the lipid bilayer of cell membranes. Therefore, for plasma proteins and other large solutes in blood, facilitated diffusion is not the method by which they cross into the tissue fluid. Instead, they either pass through larger openings such as fenestrations in capillary walls or are carried through the endothelial barrier by transcytosis.