Anatomy of the renal interstitium

The interstitium of the kidney comprises the extravascular intertubular spaces of the renal parenchyma, with their attendant cellular elements and extracellular substances. As we define it here, the interstitium is bounded on all sides by tubular and vascular basement membranes. This suggests including the lymphatics within the interstitium. That the vascular compartment on the other hand should be distinguished from the interstitium—in contrast to what is often assumed—is suggested by evidence of significant solute polarization between capillary plasma and the interstitium [1].The interstitium of the kidney is not a simple passive space in which the “true” functional units—nephrons and vessels—are embedded. Rather, it mediates and in fact modulates almost all exchange among the tubular and vascular elements of the renal parenchyma; along with segmental specialization of the nephron, it underlies the functional zonation of the kidney; it probably influences glomerular filtration through its effects on tubuloglomerular feedback; it decisively affects growth and differentiation of parenchymal cells; it determines the compliance of the peritubular micro vasculature; the cells of the interstitium produce a variety of local (autocoid) and systemic hormones; and alterations in the interstitium contribute to the clinical manifestations of renal disease.This review will deal with the various cellular and extracellular elements of the renal interstitium under normal conditions. The studies on which our conclusions are based were conducted principally in experimental animals, in particular the rat