Physiologists are looking into renal autoregulatory mechanisms in a species that closely resembles human physiology. Renal blood flow and glomerular filtration rate are measured in an anesthetized animal in response to changes in mean arterial pressure during one of their experiments. The data they collect is depicted in the graph below. Assuming a hematocrit of 0.50, what is the best estimate of the filtration fraction when the mean arterial pressure is 120 mm Hg?

Question

Physiologists are looking into renal autoregulatory mechanisms in a species that closely resembles human physiology. Renal blood flow and glomerular filtration rate are measured in an anesthetized animal in response to changes in mean arterial pressure during one of their experiments. The data they collect is depicted in the graph below.  Assuming a hematocrit of 0.50, what is the best estimate of the filtration fraction when the mean arterial pressure is 120 mm Hg?

Quizplus · Accepted Answer

Eductional Objective: The filtration fraction (FF) is the fraction of plasma flowing through the glomeruli that is filtered into Bowman's space via the glomerular capillaries. It is defined as the ratio of glomerular filtration rate (GFR) to renal plasma flow (RPF):
RPF is used to calculate FF rather than RBF because RBF includes the volume of blood occupied by erythrocytes, which is not available for filtration across the glomerular capillaries. The RPF more accurately quantifies the volume of plasma that can pass through the glomerular capillaries and can be calculated from the RBF using the following equation: 
In this case, at a mean arterial pressure of 120 mm Hg, the experimental animal has a RBF of 1.0 L/min and a GFR of 0.1 L/min. Because the hematocrit is 0.5, this gives:
Therefore, FF = (0.1 L/min) / (0.5 L/min) = 0.2.

Physiologists Are Looking into Renal Autoregulatory Mechanisms in a Species