Development of the human renal glomerulus I. Differentiation of the filtering membrane

The development of the human renal glomerulus, in particular its filtering membrane, has been studied by light microscopy with a high resolution technique as a necessary and complementary step for electron microscopical studies. The glomerular filtering membrane is a triple layered structure composed of the visceral epithelium, the capillary endothelium and a basement membrane interposed between them. These three layers have different and definite origins in the metanephrogenic blastema, but close interdependency during the developmental process exists. Mesenchymal cells were demonstrated migrating from the renal interstitium into the invaginating wall of the renal vesicle and transforming into the endothelial and mesangial cells. The visceral epithelium originates from the invaginated wall of the primitive renal vesicle and is transformed from a mass of cells into a special membrane concomitant with the differentiation of the capillary loops. The basement membrane is produced later by the close association of the other two cellular layers.