How is renal blood flow (RBF) calculated?

Renal blood flow (RBF) is an important physiological parameter that reflects the volume of blood delivered to the kidneys per unit time. The correct formula for calculating renal blood flow is based on the relationship between renal plasma flow (RPF) and hematocrit (Hct), which represents the proportion of blood volume made up by red blood cells.

The formula RBF = RPF / (1 - Hct) effectively accounts for the proportion of blood that is plasma versus cells. Since not all blood contributes to plasma flow, we need to adjust the renal plasma flow to account for the cellular component in the blood. This adjustment involves dividing the renal plasma flow by the fraction of the blood that is plasma, which is expressed as (1 - Hct). By doing so, we can accurately determine the total volume of blood flowing through the renal circulation.

The reasoning behind the other options reinforces the validity of this choice: while RPF and Hct are integral components in determining RBF, they do not maintain the correct relational formula to reflect how plasma flow and hematocrit interact in calculating overall blood flow. Therefore, the formula depicting the relationship between RBP, RPF, and Hct must include division by (1 - Hct) to