Approximately 20% of the renal plasma flow is filtered at the glomerulus, a value known as the filtration fraction. This occurs because only a portion of plasma entering the glomerular capillaries passes through the filtration barrier into Bowman's capsule. The remaining plasma exits via the efferent arteriole to participate in tubular secretion and reabsorption. Understanding the filtration fraction is crucial in assessing glomerular function and renal clearance, which has direct implications in diagnosing and managing renal diseases. An abnormally high or low filtration fraction can indicate pathological changes in glomerular hemodynamics.

Reference: Guyton and Hall Textbook of Medical Physiology, Guyton & Hall, 14th Edition.