Superficial nephron tubular-vascular relationships in the rat kidney

Abstract

Silicone rubber injections of methyl salicylate-cleared rat kidneys were performed. In 50 of 56 injections of superficial nephrons with their accompanying blood supply, the efferent vessel and early proximal tubule were closely approximated. In 18 of 21 tubular injections filling through the pars recta, the proximal tubule folded upon itself with early and late proximal segments, in close contact, located over their parent glomerulus, and the midproximal segments separate and located over their parent interlobular artery. The distribution of blood was serially through the early-late proximal region above the glomerulus via a long unbranched efferent vessel, via branches over the capsular surface, via capillaries down through the midproximal region, then into the interlobular vein. The observed anatomical pattern of the superficial nephron appears to permit direct functional interactions between the juxtaposed early and late proximal tubule, and in turn may effect midproximal function via the distribution of blood (modified by early proximal) from the efferent vessel to midproximal convolutions. In addition, the relationship between specific segments of the proximal tubule and specific portions of the postglomerular peritubular blood supply may be important in determining the distribution of peritubular physical forces to these nephrons.

Axial heterogeneity of intracellular pH in rat proximal convoluted tubule.

“…Our finding that late proximal convolutions are located near star vessels confirms our previous observations and those made by others (30)(31)(32)(33). The present studies also illustrate a surfacing pattern of proximal convolutions not previously appreciated.…”

“…The surfacing pattern of early proximal convolutions suggested to us that in superficial nephrons the initial portion of the proximal tubule must move away from its own glomerulus to later emerge in the outer region of the star vessel complex. This unfolding pattern of early proximal tubule has been shown in deeper cortical nephrons by Weinstein and Szyjewicz (33). The folding back of the proximal tubule toward its star vessel creates a countercurrent pattern of tubular fluid and capillary flows on the cortical surface.…”

“…3). The vascular portion of this system is composed of peritubular capillaries derived from penetrating branches of surface capillaries and draining into the interlobular vein located below the point where the proximal tubule folds back toward its own star vessel (31,33).…”

Vascular geometry and oxygen diffusion in the vicinity of artery-vein pairs in the kidney

“…3A). This is due to the tortuosity of capillaries and tubules located in the renal cortex (1,46). A second consideration, on which we based the reduction in V O2 with respect to the aspect ratio of the tubules, is shown in Fig.…”

“…3B. The tortuous segments of tubules and their servicing peritubular capillaries demonstrate a high degree of geometrical complexity in 3D (46). This makes it difficult to correlate the aspect ratio and V O2 for tubules obtained by sectioning of tissue along the tortuous segments of the tubules.…”