What is the Glomerular Filtration Rate (GFR)? Discuss the physiological factors that can influence it.
Generally this question was well answered. Almost all answers gave the correct value for GFR
and the correct formula for Starling’s forces across the glomerular membrane.
Better answers discussed the physiological factors affecting each force (hydrostatic and
osmotic) across the membrane in a stepwise logical manner.
Some answers discussed the control of renal blood flow; this was not expected and therefore
was not rewarded.
If this question was well answered, how come 60% of the candidates fail it?
Glomerular filtration rate (GFR) is the sum of the ultrafiltrate produced by all nephrons
Glomerular ultrafiltration is described by the Starling equation:
GFR = Kf [ (Pgc - PBC) - σ(Πgc - Πi) ]
Glomerular filtration of solutes is affected by:
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Horster, M., and K. Thurau. "Micropuncture studies on the filtration rate of single superficial and juxtamedullary glomeruli in the rat kidney." Pflüger's Archiv für die gesamte Physiologie des Menschen und der Tiere 301.2 (1968): 162-181.
Deen, William M., et al. "Dynamics of glomerular ultrafiltration in the rat. IV. Determination of the ultrafiltration coefficient." The Journal of clinical investigation 52.6 (1973): 1500-1508.
Hoang, Khoi, et al. "Determinants of glomerular hypofiltration in aging humans." Kidney international 64.4 (2003): 1417-1424.
Deen, William M., Matthew J. Lazzara, and Bryan D. Myers. "Structural determinants of glomerular permeability." American Journal of Physiology-Renal Physiology 281.4 (2001): F579-F596.