FINE STRUCTURE OF THE TRANSITIONAL EPITHELIUM OF THE DOG URETER

Abstract

The fine structure of the transitional epithelium of adult dog ureter has been studied in thin sections with an electron microscope. It is thought that the light cells represent an active stage and that the dark cells represent a less active stage of the same cell type according to the shape of nucleus and cell organella. The dark cells are also consideced as a type to be the result of pressure by adjacent cells or newly formed cells. The free luminal surface of the celis and many cytoplasmic vesicles in these cells are bounded by a thick unit membrane. These vesicles or vacuoles are considered to function as a defense of the cytoplasm, when the epithelial cells change the form. The vesicles and the plasma membrane maintain angular conformations which suggest the membrane to be unsually rigid. It is supposed that the plasma membrane of the superficial cells is the major barrier to the free flow of water from the cytoplasma into the hypertonic urine. The possible origin of the thick plasma membrane in the Golgi apparatus was shown. All the cells of the epithelium have a dense feltwork of tonofilaments which ramify throughout the cytoplasm. The ton8filaments connect frequently with intercellular desmosomes. Keratohyalinlike granules were seen in the tonofilaments.