Fig. 1.

A schematic view of glomerular ultrafiltration across the glomerular capillary. The Starling’s forces at work are the (1) glomerular transcapillary hydraulic pressure ΔP which is the difference between the glomerular and Bowman’s Space hydrostatic pressures and (2) the opposing glomerular capillary oncotic pressure (π _GC). Bowman’s Space oncotic pressure is negligible and usually disregarded. The difference between ΔP and π _GC at any given point is the net ultrafiltration pressure (P _UF). ΔP remains constant across the length of the glomerular capillary. However, because π _GC rises as plasma proteins concentrate, the rate of ultrafiltration decreases along the length of the capillary