Electron micrographs of gallbladder epithelium, a. The tall columnar cells display features typical of absorptive cells, with microvilli on their apical surface, an apical junctional complex separating the lumen of the gallbladder from the lateral intercellular space, and numerous mitochondria in the apical portion of the cell, x 3,000. b. During active fluid transport, salt is pumped from the cytoplasm into the intercellular space, and water follows the salt. Both salt and water then diffuse into the cell from the lumen. As this process continues, the intercellular space becomes greatly distended (arrows). Fluid moves from the engorged intercellular space (arrows) across the basal lamina into the underlying connective tissue (CT) and then into blood vessels. The increase in size of the lateral intercellular space during active fluid transport is evident with the light microscope, x3,000.
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