A Compendium of Urinary Biomarkers Indicative of Glomerular Podocytopathy

Figure 2

A simplified glomerulus and initial segment of the nephron are depicted; mesangia and the interweaved, capillary tuft structure are not shown to focus upon a single capillary and its related glomerular filtration apparatus. Also not depicted is the continuity between the visceral and parietal epithelial layers of the glomerulus. A glomerular capillary is lined by the fenestrated endothelia, which is intimately associated with the glomerular basement membrane (GBM). Also associated with the GBM is the visceral epithelial layer consisting of podocytes; the podocyte is made up of a cell body and processes that allow it to wrap finger-like projects about glomerular capillaries. Interposed between podocyte foot processes is a space spanned by the slit diaphragm—a key structure in the limitation of particles (based on size) from passing into the ultrafiltrate. Material/fluid that passes through the endothelia, GBM, and podocyte/slit diaphragm (these three constitute the glomerular filtration apparatus) makes it into Bowman’s space, and the fluid at this point is termed ultrafiltrate. The ultrafiltrate from here passes through the length of the nephron—with modification possible—and urinary tract. The podocytes that lay on the left side of the shown capillary (1) are shown in a normal, healthy state: foot processes exist with developed slit diaphragms in between. In contrast, the right side of the capillary exhibits podocytes of an injured phenotype (2) effacement is present (other manifestations of an injured podocyte are not depicted, but can be read about in the paper), and at times podocytes may shed material later to be found in urine. If the podocyte is injured to a certain degree, it may detach from the underlying GBM and be observed in collected urine. A GBM denuded of podocytes may develop and lend itself as a surface for adherence with the parietal epithelium.