PSIO 532 Study Guide - Final Guide: Renal Function, Efferent Arteriole, Inulin
Physiology 532 – Renal Physiology
Inulin Clearance
There are three common ways of measuring/estimating GFR:
Cinulin is the standard for measuring GFR, but is used less in human studies now (being
replaced by a substance called iothalamate that is handled similarly to inulin by the
kidney).
Clearance of Inulin
Thus, the clearance of inulin equals
the GFR
Cin = GFR = Ujn_* V
Ain
Clearance of creatinine closely
approximates the GFR.
afferent glomerulus efferent
arteriole arteriole
GFR « Ucr * V
Acr
Document Summary
There are three common ways of measuring/estimating gfr: Cinulin is the standard for measuring gfr, but is used less in human studies now (being replaced by a substance called iothalamate that is handled similarly to inulin by the kidney). afferent arteriole glomerulus efferent arteriole. Thus, the clearance of inulin equals the gfr. It is made from creatine and is converted by enzymes to creatinine in the plasma by enzymes. The amount of creatinine that is made on a daily basis is the same everyday because our muscle mass relatively stays the same day to day. Muscle is infusing creatinine at a constant rate. Secretion can be ignored in healthy individuals and if your gfr is 40-50% of normal. -> secretion would overestimate your gfr by a few percentages. However, at very low gfr (20%), the secretion can be significant and thus at very low. Gfr the creatinine clearance will overestimate gfr; ccr ~ gfr.