The structural organization of the mouse kidney.

Abstract

The structural organization of the mouse kidney has been investigated by means of standard histology procedures, by injecting the blood vessels and by injecting single nephrons. The arrangement of the nephrons establishes a zonation which, in the medulla, differs to some extend from that seen in other mammalian species. The outer medullary zone consists, in addition to outer and inner stripes, of a third part which we call the innermost stripe—due to its location between the inner stripe proper and the inner zone. As most of the short loops, at this level, have already turned back it contains almost exclusively limbs of long loops of Henle. The blood vessels exhibit the well known basic pattern of the mammalian kidney. Differences do exist, however, with respect to the morphology of the vascular bundles: frequently at the transition of outer and inner stripes, several vascular bundles unite to form large secondary bundles which extend throughout the inner stripe, recovering into the original number of bundles at the transition to the innermost stripe. The limbs of the short loops of Henle run directly through the medullary rays and the outer stripe; thereby, corresponding descending and ascending loop limbs mostly occupy a neighbouring position. At the transition of outer and inner stripes corresponding loop limbs separate from each other, the descending limb running within the vascular bundle, the ascending limb within the interbundle region. At the transition to the innermost stripe the descending limbs leave the bundles, most of them looping back with only a minority of them reaching the innermost stripe. The limbs of the long loops of Henle directly, without passing the medullary rays, penetrate or emerge from the outer stripe, respectively. Throughout the total renal medulla, corresponding limbs of long loops mostly run separated from each other. In the inner stripe their descending limbs, in contrast to those of short loops, are nerve included within a vascular bundle. In the inner zone neither of the loop limbs occupy a constant histotopographical position. The short and long loops of Henle differ both in histotopographical position and in their epithelia. Even at the light microscopic level it may be seen that the thin descending limbs of long loops are equipped with a thicker and apparently more complex epithelium than those of the short loops. The characteristic course of short and long loops of Henle in combination with the differences in the epithelial lining of their descending limbs suggest sa different function of both loops in the renal medullary concentrating process.