Fig. 2.

Upper panel: Electron micrograph illustrating a typical capillary endothelial cell with numerous caveolae. Many of these are connected to the luminal or abluminal plasma membranes (arrows), whereas others are in the cytoplasm. L, lumen scale bar, 100 nm. Lower panel: Schematic diagram illustrating pathways by which molecules can cross the capillary barrier. (1) intercellular cleft; (2) caveolae that may shuttle across the capillary or form a chain of vesicles that connect the lumen and albumen. BL, basal lamina