Glomerulus and Disorders

Abstract

The glomeruli of kidney are selective filtering corpuscles composed of a capillary network, podocytes, and mesangial cells (panel a). The glomerular basement membrane (GBM) is situated between capillary endothelia and podocytes (cf. Fig. 107). All three cell types and the GBM are important for the ultrafiltration of plasma. The fenestrated endothelia (arrowheads in panel b) face the blood and differ from other fenestrated endothelia (cf. Fig. 148), with their larger size of pores and lack of diaphragms. The podocytes protrude in the urinary space (US) and their peculiar shape is best appreciated by scanning electron microscopy (panel c). From their cell body, long ramifications originate, the primary processes, which embrace the capillaries. From them, interdigitating secondary processes originate, the foot processes, which form the narrow filtration slits (30–40 nm wide) that are bridged by slit diaphragms (arrows in panel b). Slit diaphragms resemble adherens intercellular junctions and mark the border between the apical and basal podocyte plasma membrane. The foot process base inserts into the GBM. The transmembrane proteins podocalyxin and podoplanin as well as the podocyte-associated talin 1 are important for the shape of podocytes.