The inner medulla of rabbit's kidney was examined for the total internal circumferences of Henle's thin segments and collecting tubules at a given medullary height. The results could be approximated by H(x)=168 (e0.60x-1) for Henle's thin segments and A(x)=114 (e0.39x-1) for the collecting tubules. In the expressions x is a distance in mm taken along a medullary ray from the medullary apex to a certain point of the inner medulla, and H(x) and A(x) give the total internal circumferences in mm of Henle's thin segments and collecting tubules respectively on a curved surface defined by x. As indicated by different exponents in H(x) and A(x), quantitative predominance of Henle's thin segments over collecting tubules toward the external border of the inner medulla was demonstrated. This was also an expression that in the pile of Henle's loops short loops were overwhelmingly larger in number than long ones. On the assumption that Henle's loops supply sodium to the interstitial tissue and produce a gradient of sodium concentration rising toward the medullary apex, the structural principle of the inner medulla would counteract the effect. Our histometrical analysis did not consequently favor the counter-current hypothesis. The above equations are to be used in our forthcoming mathematical analysis on the mechanism of urinary concentration. © 1969, Tohoku University Medical Press. All rights reserved.
