Observations on the Ultrastructure and Genesis of Urinary Calculi

Abstract

Conventional and scanning electron microscopy of calcigerous renal calculi disclosed typical concentric laminations, radial striations and microspherules. Random axial distribution of oxalate crystals and their coating by electron-dense matrix fibers wtih a definite parallel orientation and cross-linkages were evident. The biochemical relationship of uromucoid to matrix substance A is described. Renal sialidase may convert the urinary uromucoid to matrix substance A, whose apatite-covered fibers may be responsible for epitaxial nucleation of some crystal systems. The intimate apatite-matrix relationship occurred in the human nephron, probably as an intracellular phenomenon. Subsequent extrusion of these mineralized complexes into the lumen of the nephron (intranephronic calculosis) may, in some instances, represent the initial microanatomic stage of renal calculogenesis.