What is the formula for net filtration pressure?

The formula for net filtration pressure (NFP) is designed to assess the balance of forces that determine how fluids move across capillary membranes, particularly in the context of renal physiology where it impacts glomerular filtration. The correct formulation takes into account the hydrostatic and oncotic pressures involved.

In the correct formula, net filtration pressure is defined as the difference between the hydrostatic pressure in the capillary (Pc) and the interstitial fluid pressure (Pi), minus the difference between the oncotic pressure in the capillary (∏c) and the oncotic pressure in the interstitium (∏i). This relationship can be summarized as:

Pnet = (Pc - Pi) - (∏c - ∏i)

This indicates that the net filtration pressure is influenced not only by the hydrostatic forces pushing fluid out of the capillaries but also by the oncotic pressures that tend to pull fluid back into the capillaries. Understanding this balance is crucial for evaluating how well the kidneys filter blood and regulate fluid balance in the body.

The other proposed options do not accurately represent the factors involved in net filtration pressure. For example, using a positive sign instead of a negative one when calculating the effects of oncotic pressure leads