A researcher is studying the effect of various manipulations on kidney blood flow and glomerular filtration. Which of the following is most likely to both decrease renal plasma flow and increase the filtration fraction?

Question

A researcher is studying the effect of various manipulations on kidney blood flow and glomerular filtration.  Which of the following is most likely to both decrease renal plasma flow and increase the filtration fraction?

Quizplus · Accepted Answer

Constriction of the efferent (outgoing) arteriole will impede blood flow through the kidney. This will decrease RPF, but will increase glomerular capillary hydrostatic pressure as the fluid "backs up" in the glomerulus, increasing hydrostatic pressure. As described below, this increased glomerular hydrostatic pressure will cause an increase in the filtration fraction. 11ec160b_3cf4_570f_9249_6debd05a37a8_MD0001_00 The renal plasma flow (RPF) is the volume of plasma that is delivered to the kidney per unit time. The RPF is provided by the renal blood flow, which delivers both erythrocytes and plasma to the kidney. The RPF is theoretically calculated by subtracting the amount of erythrocytes (hematocrit) from the total renal blood flow. Clinically, however, RPF is generally estimated by calculating the paraaminohippuric acid (PAH) clearance. RPF is linked to the glomerular filtration rate (GFR) and the filtration fraction (FF) by the following equation: FF = GFR / RPF The filtration fraction refers to the proportion of the RPF that is filtered from the glomerular capillaries into Bowman's space and is expressed as a percentage. Using the equation above, one can observe that increases in GFR or decreases in RPF will increase the FF. The GFR is dependent on hydrostatic and oncotic pressures in the glomerular capillaries and Bowman's space and can be calculated with the following equation: GFR = K_f ((P_G - P_B) - (π_G - π_B)) Where Kf refers to the coefficient of filtration, P_G refers to the hydrostatic pressure in the glomerular capillaries, P_B refers to the hydrostatic pressure in Bowman's space, π_G refers to the oncotic pressure in the glomerular capillaries and π_B refers to the oncotic pressure in Bowman's space. Increases in the glomerular capillary hydrostatic pressure or the Bowman's space oncotic pressure will increase GFR, while increases in capillary oncotic pressure or Bowman's space hydrostatic pressure will decrease GFR. (Choice A) Hyperproteinemia causes increased glomerular capillary oncotic pressure thereby decreasing GFR. This will have no effect on the RPF, but will cause a decreased FF due to the decreased GFR. (Choice B) Bladder neck obstruction causes an increase in Bowman's space hydrostatic pressure thereby decreasing GFR. This too will have no effect on the RPF, but will cause a decreased FF due to the decreased GFR. (Choice D) Constriction of the afferent (incoming) arteriole causes a decrease in glomerular capillary hydrostatic pressure leading to a decreased GFR. RPF is also decreased by this process. The FF remains unchanged due to decreases in both GFR and RPF. (Choice E) Dilation of the efferent arteriole causes decreased glomerular capillary hydrostatic pressure leading to a decrease in GFR. The RPF is increased by this process, and the FF is decreased due to the decrease in GFR and increase in RPF. Educational Objective: Increases in the capillary hydrostatic pressure or the Bowman's space oncotic pressure will increase GFR, while increases in capillary oncotic pressure or Bowman's space hydrostatic pressure will decrease GFR. The filtration fraction (FF) can be calculated by dividing the GFR by the renal plasma flow (RPF). Increases in GFR or decreases in RPF will increase the FF.

A Researcher Is Studying the Effect of Various Manipulations on Kidney