The image shows cell membranes of two neighboring endothelial cells #1 and #2. Each membrane looks like a trilaminar structure comprising two dark sheets (electron-dense ones) and a clear zone between them. The zone is hydrophobic and shared by both lipid layers of the membrane. Integral membrane proteins, which are embedded into the lipid bilayer, are usually not visible. Tight (or occluding) junctions (for more details, see cit10), connect the neighboring epithelial cells. The junctions close the intercellular space and control both its size and the flow capacity between the vessel lumen and the interstitial space around the capillary.

In the cytoplasm one of these cells contains a rounded vesicle, which is also formed by the membrane. About a half of this vesicle’s surface is clathrin-coated; another other half has no coating. Clathrin-coated vesicles appear result from cell membrane invaginations (for more details, see cit15).

The orifice of a caveola, which is a plasma membrane invagination, is blocked by a thin single-layered diaphragm. The basal lamina underlies cell membranes from the side of interstitial space. The basal lamina is present in epithelial cells strata that are attached to it.