GLOMERULAR FILTRATION RATE

• The volume of ultrafiltrate formed by all of the nephrons of the kidneys per minute;
• Units = mL/min.
• Typical healthy GFR is between 110-130 mL/min; it varies based on sex, body composition, age, and other factors.

GFR is directly proportional to:

• Filtration membrane permeability
• Surface area available for filtration
• Net filtration pressure is largely influenced by hydrostatic glomerular capillary pressure (PGC), which is easily adjusted by altering blood flow through the glomerulus.
• Of the three variables that determine GFR, net filtration pressure is the easiest to manipulate.

Key Relationships:

Baseline:

• Constant supply of renal blood flows through the afferent arteriole, glomerulus, and efferent arteriole.
• Constant hydrostatic capillary pressure.
• Constant GFR.

Afferent Arteriole Constriction:

• Reduces renal blood flow
• Reduces hydrostatic capillary pressure
• Reduces GFR

Afferent Arteriole Dilation:

• Increases renal blood flow
• Increases hydrostatic capillary pressure
• Increases GFR

Efferent Arteriole Mild Constriction:

• Decreases renal blood flow
• Increases hydrostatic capillary pressure
• Increases GFR

Efferent Arteriole Extreme Constriction:

• Decreases renal blood flow
• Increases capillary oncotic forces
• Decreases GFR

Efferent Arteriole Dilation:

• Increases renal blood flow
• Decreases hydrostatic capillary pressure
• Decreases GFR

Clinical Correlations:

• GFR is clinically measured to evaluate kidney functioning.
• GFR can be altered by medications that cause vasoconstriction or vasodilation.