Distribution of Blood in the Functional Kidney

Abstract

It has long been known that the kidney, in its functioning state, is distended with blood (1-4). Rose-Bradford (1) stressed the "passive" character of this distension, for he noted that the kidney swelled when the blood pressure rose and shrank when it fell. Text- fig. 1 shows how the organ collapses when its circulation is abruptly cut off; in this instance, although drainage was obviously incomplete, it shrank from a volume of 49 cc. to a volume of 39 cc., showing that at least 20 per cent of its normal functioning volume was distending fluid. This fluid drains from the renal vein when the renal artery is occluded; in quantity, when drainage is complete, it averages 26 per cent of the functionally distended kidney (5, 6).This aspect of renal behavior has, however, been overlooked by those investigating the functional vascular morphology of the organ. Led recently by Trueta el al. (7), many studies of blood distribution have been attempted, using particularly the technic of injecting India ink into the vascular system and then, at necropsy, examining the distribution of ink. In such studies, the distribution of ink at necropsy should reflect the distribution while the organ is functioning. But if the kidney's blood were to drain out after removal, the subsequent localization of the dye would give only very rough information about the distribution of blood in the functioning organ. The latter is not thoroughly known and hence the present study was undertaken.Actually, the fluid naturally distending the kidney is not blood alone; rather, it is a fluid containing less red cells and less plasma protein than simultaneously drawn blood, the same amount of Na and Ca, and increased quantities of K, C1, urea, and PO4 (6). Because kidney interstitial fluid (or lymph) has approximately this same composition, we have concluded that the distending fluid is very probably a mixture of blood and interstitial fluid. Furthermore, since the distending fluid contains only about half the red cells that blood contains (6), the volume of its two components, in terms of percentage of the functionally distended kidney, is 13 per cent blood and 13 per cent interstitial fluid.

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