Figure 135

Mechanisms of proximal tubule cell—mediated reductions in glomerular filtration rate (GFR) following ischemic injury. A, GFR depends on four factors: 1) adequate blood flow to the glomerulus; 2) an adequate glomerular capillary pressure as determined by afferent and efferent arteriolar resistance; 3) glomerular permeability; and 4) low intratubular pressure. B, Afferent arteriolar constriction diminishes GFR by reducing blood flow—and, therefore, glomerular capillary pressure. This occurs in response to a high distal sodium delivery and is mediated by tubular glomerular feedback. C, Obstruction of the tubular lumen by cast formation increases tubular pressure and, when it exceeds glomerular capillary pressure, a marked decrease or no filtration occurs. D, Back-leak occurs when the paracellular space between cells is open for the flux of glomerular filtrate to leak back into the extracellular space and into the blood stream. This is believed to occur through open tight junctions.

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