Which formula calculates the net filtration pressure (NFP)?

The net filtration pressure (NFP) is a crucial concept in renal physiology as it influences the formation of urine. It reflects the balance of forces favoring and opposing filtration in the renal corpuscle. The correct formula for calculating NFP is derived from the forces at play:

NFP is the net result of the glomerular blood hydrostatic pressure (GBHP), which promotes filtration, opposing it is the capsular hydrostatic pressure (CHP) and the blood colloid osmotic pressure (BCOP) that resist filtration.

In the correct formula, GBHP is taken as a positive force since it pushes fluid out of the capillaries into the Bowman’s capsule. Conversely, CHP and BCOP are subtracted because they work against this filtration process. CHP refers to the pressure of the fluid already in the capsule that opposes the entry of more fluid, while BCOP represents the osmotic pressure due to proteins in the blood that draws fluid back into the capillaries.

Thus, the formula NFP = GBHP - CHP - BCOP accurately combines these pressures: it adds the promoting force (GBHP) and subtracts the opposing forces (CHP and BCOP), leading to a clear understanding of how much net fluid is