Physiologists are investigating renal autoregulatory mechanisms in an animal species that closely mimics human physiology. During one of their experiments, renal blood flow and glomerular filtration rate are measured in an anesthetized animal in response to changes in mean arterial pressure. The data they obtain is shown on 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 investigating renal autoregulatory mechanisms in an animal species that closely mimics human physiology.  During one of their experiments, renal blood flow and glomerular filtration rate are measured in an anesthetized animal in response to changes in mean arterial pressure.  The data they obtain is shown on 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

The filtration fraction (FF) is the fraction of plasma flowing through the glomeruli that is filtered across the glomerular capillaries into Bowman's space. It can be thought of as the ratio between the glomerular filtration rate (GFR) and renal plasma flow (RPF): RPF is used to calculate FF rather than renal blood flow (RBF) because RBF includes the volume of the blood that is occupied by erythrocytes, a volume unavailable for filtration across the glomerular capillaries. The RPF quantifies the volume of plasma that is able to pass through the glomerular capillaries more accurately 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. Educational objective: The filtration fraction is the fraction of plasma flowing through the glomeruli that is filtered across the glomerular capillaries into Bowman's space (FF = GFR/RPF). Renal plasma flow can be determined from renal blood flow by multiplying the renal blood flow by (1 - Hematocrit).

Physiologists Are Investigating Renal Autoregulatory Mechanisms in an Animal Species