Describe the factors that determine glomerular filtration rate (GFR) in the kidney
(70% of marks). Outline methods by which GFR can be measured (30% of marks).
Good answers included a description of Starling forces acting at the glomerular basement
membrane. A description of the local and systemic factors influencing each component was
It was expected candidates would discuss autoregulation of GFR & RBF, tubuloglomerular
feedback, and integrated responses the body uses to keep GFR steady.
Confusion about the nature of induced effects on afferent or efferent arteriolar dilation and
constriction limited marks for some candidates. Many failed to mention the effects of mesangial
surface area, Bowmans space pressure or serum protein content.
Candidates were expected to outline the methods of GFR estimation. Better responses
described the rationale behind the use and limitations. Creatinine clearance, inulin and nuclear
medicine techniques all scored marks. Some candidates made no attempt at this section and
missed the opportunity to score marks. Estimates of CrCl/GFR [eGFR by formulae such as
Cockcroft Gault, and serum Cr] are not measurement of GFR.
Glomerular ultrafiltration is described by the Starling equation:
GFR = Kf [ (Pgc - PBC) - σ(Πgc - Πi) ]
Regulation of glomerular ultrafiltration is achieved by controlling the vascular resistance of the afferent and efferent arterioles, via these factors:
As for "outline methods by which GFR can be measured", we're going to assume the examiners meant "briefly, in three minutes, list all the methods and marker substances you can think of". Thus:
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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.
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