Describe the factors that determine the filtered load of a substance at the renal glomerulus.
A good place to start was with the correct equation for a filtered load and a description of the
components. Better answers described the components and how they differ and change over
the glomerulus. Many candidates usefully based answers around the Starling forces.
A summary of factors including the role of plasma concentration, protein binding, molecular size
and charge was required to pass. Many answers gave examples for the effects of size and
charge and relate endocrine responses to specific alterations in arteriolar tone and how this
affected filtration. A detailed discussion of cardiovascular and endocrine responses to
hypovolaemia was not required.
Some candidates confused clearance with filtered load. Candidates are reminded to write
legibly - especially where subscripts and Greek letters are used. Directional arrows (if used)
should correlate with text.
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:
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