STRUCTURE-STABILIZING FORCES IN THE GLOMERULAR TUFT

The glomerular tuft is constantly exposed to considerable expansile fo rces resulting from high capillary pressures. Counterforces must be ge nerated in order to maintain structural stability. This review analyze s those structures of the glomerular tuft capable of developing such s tabilizing forces. Two systems are described. A basic system consists of the glomerular basement membrane (GBM) and the mesangium. The GBM r epresents the main skeletal element of the glomerular tuff. In general , opposing portions of the GBM are bridged by contractile mesangial ce ll processes, generating inwardly directed forces that balance the exp ansile forces resulting from pressure gradients across the GBM. A seco nd structure-stabilizing role of the podocytes appears to be superimpo sed on this system. Podocytes are attached to the GBM by numerous foot processes that contain a contractile system. The foot process attachm ents probably stabilize small patches of the underlying GBM, counterac ting local elastic distension. In addition, podocytes may contribute t o the stabilization of the folding pattern of the tuff by linking neig hboring capillary loops to each other.