ELECTRON ^IKKOSCOPY 



cells. Tlie intor('alat(Hl coll has a large luunbcr 

 of sphorical initDchoiulria wliich arc clustered 

 mostly above the nucleus, thus giving the 

 cell a dark appearance which has lead some 

 investigators to call it a dark cell (Fig. 10). 

 This seems justifiable when considering that 

 the main cell type has few mitochondria and 

 a light cyt(»i)lasni. This cell is therefore called 

 a light cell. There are other structurally 

 important differences between the two cell 

 types. The luminal surface of the dark cell 

 usuall}^ has quite abundant microvilli, 

 whereas the light cell has few or none. The 

 vesicles of the luminal part of the dark cell 

 cytoplasm and the RNA-granules are numer- 

 ous as against a scarcity of these structures 

 in the light cell. The similarity between the 

 dark intercalated cells of the cortical collect- 

 ing duct and the cells of the distal convolu- 

 tion strongly suggests that the former ac- 

 tually represents a certain variety of cells of 

 the distal convolution which are distributed 

 along the cortical collecting duct. 



Collecting Tubule. The collecting tubule 

 begins in the outer cortex and runs in a 

 straight course toward the medulla, each 

 nephron being connected to a collecting tu- 

 bule by the cortical collecting duct. The con- 

 vergence of successive orders of collecting 

 tubules in progressively deeper layers gives 

 rise to vessels of mcreasing caliber until fi- 

 nally the papillary ducts are reached. These 

 ducts discharge their contents into the renal 

 pelvis. 



It is believed that very few processes re- 

 lated to the composition of the urine occur 

 in the collecting tubule. The final concentra- 

 tion of the urine seems, however, to be estab- 

 lished here, possibly mediated by a certain 

 reabsorption of sodium chloride. It has also 

 been suggested that the permeability of the 

 cells of the collecting tubules may be in- 

 fluenced by the action of the antidiuretic 

 hormone (ADH) of the pituitary. 



Structurally, the cells of the collecting 

 tubule are rather poor (Fig. 7). The cells are 

 of a cuboidal type with a very light cyto- 



plasm containing a small amount of IINA- 

 particles and a few small and widely scat- 

 tered spherical mitochondria. Large granules 

 of the lipid type occur frequently, together 

 with a small Golgi complex. The luminal sur- 

 face displays a varying number of very short 

 microvilli and the basal plasma membrane 

 shows remnants of extremely shallow infold- 

 ings. The cell borders are straight and the 

 cells are held together by distinct terminal 

 bars close to the surface. The nuclei are 

 fairly large, occupying a good portion of the 

 cell body. 



REFERENCES 



Sjostrand, F. S. and Rhodin, J., "The ultra- 

 structure of the proximal convoluted tubules 

 of the mouse kidney as revealed by high reso- 

 lution electron microscopy," Exper. Cell Re- 

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Hall, B. V., "Studies of the normal glomerular 

 structure by electron microscopy," Proc. 

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 p. 1, 1953. 



Rhodin, J., "Correlation of ultrastructural or- 

 ganization and function in normal and experi- 

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 1954, Karolinska Institutet. 



Pease, D. C, "Fine structures of the kidney seen 

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HalL; B. v., "Further studies of the normal struc- 

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Rhodin, J., "Electron microscopy of the glomeru- 

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Pease ; D. C, "Electron microscopy of the vascu- 

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Pease, D. C, "Electron microscopy of the tubular 

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RusKA, H., Moore, D. H., and Weinstock, J., 

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Rhodin, J., "Anatomy of kidney tubules," Int. 

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Rhodin, J., "Ergebnisse der elektronenmikros- 

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