Reduction in GFR



As noted in Chapter 28, the rate of glomerular filtration may fall as a result of a decrease in cap­illary hydrostatic pressure, a change in the rate of rise of capillary oncotic pressure, or a decrease in the permeability of the capillary wall. Endothelial cell swelling, capillary occlusion or sclerosis, and glomerular scarring all decrease glomerular cap­illary pressure and blood flow. In other cases, glo­merular architecture is little affected. In animals, a reduction in the permeability (Kf) of the glo­merular capillary has been found in similar cir­cumstances.

Even when glomerular permeability is reduced, GFR can be maintained near normal by raising the hydrostatic pressure and/or blood flow within the glomerular capillary bed. This may be accom­plished by relaxation of the tone of the afferent arteriole relative to the efferent arteriole. Vaso­active agents of renal origin appear to participate in this response. In some glomerular diseases, a progressive fall in GFR is seen, continuing long after any evidence for immunological injury can be found. In such cases, these adaptive hemody­namic changes in the glomerulus lead to physical, nonimmunological injury of the glomerular cap­illaries and result in progressive glomerular scle­rosis.