In renal physiology, what primarily drives glomerular filtration across the filtration barrier into Bowman’s space?

• A. Peristaltic contractions of the ureter generating suction at the glomerulus
• B. Net filtration pressure produced mainly by glomerular capillary hydrostatic pressure
• C. High hydrostatic pressure in Bowman’s space pushing fluid into the glomerular capillaries
• D. Active transport of Na+ from the glomerular capillaries into Bowman’s space

Answer: (B)

Verified step by step guidance

1. Understand that glomerular filtration is the process by which fluid is filtered from the blood in the glomerular capillaries into Bowman’s space in the kidney nephron.
2. Identify the forces involved in filtration, which include hydrostatic pressures and osmotic (oncotic) pressures acting across the filtration barrier.
3. Recognize that the primary driving force for filtration is the net filtration pressure (NFP), which is calculated by the equation: \(\text{NFP} = P_{GC} - P_{BS} - \pi_{GC}\), where \(P_{GC}\) is the glomerular capillary hydrostatic pressure, \(P_{BS}\) is the hydrostatic pressure in Bowman’s space, and \(\pi_{GC}\) is the oncotic pressure of the glomerular capillary blood.
4. Note that the glomerular capillary hydrostatic pressure (\(P_{GC}\)) is the main force pushing fluid out of the capillaries into Bowman’s space, overcoming the opposing pressures.
5. Conclude that peristaltic contractions of the ureter, active transport of Na+, or high hydrostatic pressure in Bowman’s space do not primarily drive filtration; instead, it is the net filtration pressure dominated by glomerular capillary hydrostatic pressure.