Glomerular Filtration and GFR

Determinants of GFR

Glomerular filtration rate (GFR) is determined by the net filtration pressure across the glomerular capillaries. This pressure arises from the balance between hydrostatic pressures and oncotic pressures. The net filtration pressure can be expressed as $P_{net}=(P_{gc}-P_{bs})-({\pi }_{gc}-{\pi }_{bs})$, where $P_{gc}$ is glomerular capillary hydrostatic pressure, $P_{bs}$ is Bowman's space hydrostatic pressure, ${\pi }_{gc}$ is glomerular capillary oncotic pressure, and ${\pi }_{bs}$ is Bowman's space oncotic pressure.

Regulation of GFR

GFR is regulated by changes in arteriolar resistance. Constriction of the afferent arteriole decreases glomerular capillary pressure and thus decreases GFR. Conversely, constriction of the efferent arteriole increases glomerular capillary pressure and increases GFR.

Clinical Significance

Normal GFR is approximately 125 mL per minute. GFR is a key indicator of renal function in clinical practice, used to assess kidney health and diagnose conditions like chronic kidney disease.

Common Pitfalls

A common mistake is confusing the effects of afferent and efferent arteriole constriction on GFR. Remember that afferent constriction reduces GFR, while efferent constriction increases it, but excessive efferent constriction can lead to reduced renal blood flow.

Summary

• GFR is determined by net filtration pressure from hydrostatic and oncotic pressure differences across glomerular capillaries.
• Normal GFR is approximately 125 mL per minute.
• Afferent arteriole constriction decreases GFR, while efferent arteriole constriction increases it.
• GFR is a critical clinical measure of renal function.