Abstract
Summary
Measurements of the dimensions of proximal and distal tubules were made on nephrons obtained by microdissection from the kidneys of three female dogs. In any nephron, the length, average cross section, and volume (as for a cylinder) of the proximal tubule from its attachment to the glomerulus to the thin portion of Henle's loop were always larger than the same values for the distal tubule measured from the point of attachment to the glomerular vascular pole to entry into the collecting tubule. Proximal-distal volume ratios averaged 5.34 ± 1.32 (SD), 5.88 ± 1.46, and 7.59 ± 1.51 for each of the three dogs. The proximal convolutions accounted for 74.8 ± 9.1%, 71.0 ± 7.6%, and 77.0 ± 6.0% of the total proximal volume in the same animals. The convolutions bulked equally large in the distal tubule, making up 75.3 ± 10.9%, 70.0 ± 10.3%, and 69.1 ± 9.3% of the total, respectively. Proximal convolutions exceeded distal convolutions in volume, with ratios of 5.46 ± 1.97, 5.66 ± 1.67, and 8.95 ± 2.25 times, respectively. The volumes of proximal and distal tubules in the same nephron were significantly correlated in keeping with an intersegmental functional balance between residual filtered load leaving the proximal tubule and the capacity of the distal tubule to deal with it. The relative size of proximal and distal convolutions suggests that proximal reabsorbate determines the microenvironment of the distal convolutions.
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