The glomerulus is a capillary bed enclosed by Bowman's capsule. The filtration membrane' separating the blood plasma and the filtrate in the capsule is impermeable to large plasma proteins but permits the passage of water, electrolytes and small molecules. The filtrate formed passes into the proximal convoluted tubule (PCT).
The afferent arteriole supplies the glomerulus with blood. Blood leaves the glomerulus via the efferent arteriole that quickly gives rise to the peritubular capillaries.
There are three factors that control the volume of filtrate (F) produced from blood plasma.
The pressure against the inside of the capillary wall is called blood hydrostatic pressure (HPb). An increase in blood pressure (BP) will increase the hydrostatic pressure as indicated by the solid arrow.
The block arrow labeled F represents the filtrate entering the capsule. An increase in blood hydrostatic pressure (HPb) will increase the volume of filtrate (F) formed as indicated by the solid arrow between these two symbols.
Because the 'filtration membrane' is impermeable to large plasma proteins they accumulate in the remaining plasma. This increases the blood osmotic pressure (OP) causing water to return to the plasma from the filtrate. Thus, as osmotic pressure increases the net volume of filtrate decreases as indicated by the dashed arrow.
Filtrate accumulation inside Bowman's capsule establishes a capsular hydrostatic pressure (HPc) that opposes the formation of additional filtrate. This is represented by the dashed arrow pointing back to the block filtration arrow.
Last Updated: 7/19/2005