13. Filtration

Question 1

renal filtration fraction - definition

Answer 1

is the ratio of the glomerular filtration rate ( GFR) to the renal plasma flow ( RPF)

Question 2

Renal filtration fraction - calculation and normal value

Answer 2

FF = GFR / RPF = 20% ( normally)

Question 3

filtered load calcularion

Answer 3

filtered load ( mg /min) = GFR ( ml/min ) x plasma concentration

Question 4

• How is the filtration fraction for a molecule determined? What is the expected filtration fraction in a healthy individual?

Answer 4

By determining the ratio of the glomerular filtration rate to renal plasma flow; it is normally around 20%

Question 5

• Prostaglandins are infused into a rat’s renal arteries. What effects do they have on the glomeruli? What drug class can block them

Answer 5

They preferentially dilate afferent arterioles, increasing both the GFR and the RPF to keep the FF constant; NSAIDs

Question 6

• Angiotensin II (AT II) is infused into a rat’s renal arteries. What effects does it have on the glomeruli? What drug class can block it?

Answer 6

AT II preferentially constricts efferent arterioles, increasing GFR and decreasing RPF to increase FF; ACE inhibitors

Question 7

• Prostaglandins ____ (increase/decrease) renal plasma flow and ____ (increase/decrease) glomerular filtration rate.

Answer 7

Increase; increase

Question 8

• ____ (Prostaglandins/Angiotensin II) alter(s) renal plasma flow and glomerular filtration rate such that filtration fraction is maintained.

Answer 8

Prostaglandins (increase both renal plasma flow and glomerular filtration rate) (inhibited by NSAIDs)

Question 9

• In terms of filtration in the glomerulus, the filtered load is equal to the glomerular filtration rate multiplied by what?

Answer 9

The plasma concentration

Question 10

• Angiotensin II ____ (increases/decreases) renal plasma flow and ____ (increases/decreases) glomerular filtration rate.

Answer 10

Decreases; increases

Question 11

• A man takes an ACE inhibitor. How does its blockage of angiotensin II (AT II) affect the filtration factor (FF)?

Answer 11

FF decreases (renal plasma flow increases, and the glomerular filtration rate decreases)

Question 12

• A man takes several capsules of extra-strength ibuprofen. What effect does this have on his afferent arterioles in his kidneys?

Answer 12

NSAIDs block prostaglandins’ dilatory effect on afferent arterioles, thus his afferent arterioles constrict, which decreases GFR and RPF

Question 13

• A patient’s GFR is 125 mL/min, and RPF is 500 mL/min. What is the filtration fraction (FF)?

Answer 13

FF = GFR/RPF = (125 mL/min)/(500 mL/min) = 0.25 = 25%

Question 14

• After a patient whose GFR is 125 mL/min takes a drug, a plasma concentration of 10 mg/mL is measured. What is the filtered load (mg/min)?

Answer 14

Filtered load = GFR × plasma concentration = 125 mL/min × 10 mg/mL = 1250 mg/min

Question 15

• GFR can be estimated with ____ clearance; RPF is best estimated with ____ clearance.

Answer 15

Creatinine; PAH