G. Carl Huber

The significance of the structure of the medullary loop of the renal tubule of mammalia

A method of maceration has been devised recently 1 by means of which it is possible to isolate the entire renal tubule of adult mammals. Certain of the renal tubules thus isolated have been stained and permanently mounted in glycerine. This enables a study of their form in a manner hitherto not possible and admits of an accurate determination of their epithelial lining. Each mammalian renal tubule possesses four types of epithelium: (1) The pavement epithelium surrounding the glomerulus and lining the glomerular capsule; (2) the specific renal epithelium of the proximal convoluted portion and its medullary segment; (3) the pavement epithelium of the medullary loop; (4) the cubic or short columnar epithelium of the ascending or distal arm of the medullary loop and the distal convoluted portion. The following table shows the distribution of the last three types of epithelium in renal tubules of the rabbit, the tubules selected representing A, a tubule with renal corpuscle situated at the periphery of the cortex; B, a tubule with renal corpuscle situated in the deeper portion of the outer half of the cortex; C, a tubule the renal corpuscle of which is situated in the deepest part of the cortex. The tubules selected represent type tubules and were selected with a view of drawing attention to the fact that the character of the tubule, and perhaps also its functions, changes with the position of the renal corpuscle in the cortex. Tubules with renal corpuscles situated near the periphery of the cortex possess short medullary loops with short segments lined by pavement epithelium. The deeper in the cortex the renal corpuscle is situated the longer becomes the medullary loop and the longer the segment of the loop lined by pavement epithelium.