Final answer:
Large solutes can diffuse through endothelial cells via intracellular clefts or by being encapsulated within vesicles by endocytosis and exocytosis. Fenestrations in capillary walls allow passage of substances based on size and electric charge, while osmosis facilitates bulk flow of water.
Step-by-step explanation:
Large solutes can diffuse through the endothelial cells via different pathways. One such pathway is through intracellular clefts, which are gaps between endothelial cells that allow certain substances to pass. Another mode of transport for large solutes, including large plasma proteins, is through endocytosis and exocytosis; this involves the substances being packaged into vesicles within the endothelial cells before being transported in or out. Additionally, large molecules can pass through fenestrations in the capillary walls, which are small openings that permit the passage of substances primarily based on size, with most substances crossing readily if they are less than 4 nm and up to 8 nm in size.
The capillary endothelium also prevents the filtration of blood cells or large proteins, allowing other constituents through. Factors affecting the movement of substances through fenestrations include size, electric charge, and presence of the basement membrane, which filters medium-to-large proteins. The net movement of water across capillary walls, known as bulk flow, takes place via another process called osmosis, which is essential in regulating the distribution of water in the body's compartments.