Transmission electron micrograph of the apical portion of a transitional epithelial cell. a. The cytoplasm displays small vesicles, filaments, and mitochondria, but the most distinctive feature of the cell is its fusiform vesicles (FV). x27,000. b. The higher magnification shows that the membrane forming the vesicles appears to be similar to the plasma membrane of the cell surface (arrows). Both membranes are thickened and give the impression of possessing a degree of rigidity greater than that of plasma membrane in other locations. The thickened plasma membrane represents a sectioned view of a surface plaque. The fusiform vesicles are formed by the infolding of the plaques in the cells of the relaxed urinary bladder, x 60,000.
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