In renal physiology, what pressure gradient directly drives glomerular filtration from the glomerular capillaries into Bowman's space?

• A. Active transport of sodium by the proximal tubule creating water flow
• B. Net filtration pressure (NFP) created by the balance of glomerular capillary hydrostatic pressure, Bowman's space hydrostatic pressure, and plasma oncotic pressure
• C. The osmotic gradient between the cortical and medullary interstitium
• D. Peristaltic contractions of the ureter generating suction at the renal pelvis

Answer: (B)

Verified step by step guidance

1. Identify the process involved: Glomerular filtration is the movement of fluid from the glomerular capillaries into Bowman's space in the nephron of the kidney.
2. Understand the forces at play: Filtration is driven by pressure gradients across the capillary walls, specifically hydrostatic and oncotic pressures.
3. Define the key pressures: Glomerular capillary hydrostatic pressure pushes fluid out of the capillaries, Bowman's space hydrostatic pressure opposes this movement by pushing fluid back, and plasma oncotic pressure (due to plasma proteins) also opposes filtration by pulling water back into the capillaries.
4. Combine these pressures to find the net driving force: The Net Filtration Pressure (NFP) is calculated by subtracting the opposing pressures from the glomerular capillary hydrostatic pressure using the formula: \[\text{NFP} = P_{GC} - P_{BS} - \pi_{GC}\] where \(P_{GC}\) is glomerular capillary hydrostatic pressure, \(P_{BS}\) is Bowman's space hydrostatic pressure, and \(\pi_{GC}\) is plasma oncotic pressure.
5. Recognize that this Net Filtration Pressure (NFP) is the direct pressure gradient responsible for driving glomerular filtration from the capillaries into Bowman's space.