Updated: 9/4/2020

Filtration

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Introduction
  • Filtration fraction (FF) represents the ratio between glomerular filtration rate (GFR) and renal plasma flow (RPF)
    • this in turn represents which fraction of RPF becomes filtered via the glomerular capillaries
      • the normal filtration fraction is ~20% and thus implies that 80% of the RPF is not filtered
        • the unfiltered RPF will then be part of the peritubular capillary blood flow after entering the efferent arteriole
    • Filtration fraction (FF) = GFR / RPF
    • Filtered load = GFR x plasma concentration
  • Renal plasma flow (RPF)
    • can be determined by using clearance of para-aminohippuric acid (PAH)
      • RPF = [U(PAH) x V] / [RA(PAH) - RV (PAH)]
        • U(PAH) = urine concentration of PAH (mg/mL)
        • V = urine flow rate (mL/min)
        • RA(PAH) = renal artery concentration of PAH (mg/mL)
        • RV(PAH) = renal vein concentration of PAH (mg/mL)
    • determining the RPF will allow you to determine the renal blood flow (RBF)
      • RBF = RPF / (1 - hematocrit)
 
Changes in Starling Force and Its Effect On RPF, GFR, and FF
Condition
RPF
GFR FF (GFR/RPF)
Afferent arteriole constriction
  • Unchanged
Efferent arteriole constriction

↑ plasma protein concentration
  • Unchanged
↓ plasma protein concentration
  • Unchanged
Ureter constriction
  • Unchanged

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Questions (5)
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(M1.RL.12.69) A healthy 30-year-old female has a measured creatinine clearance of 100 mL/min. She has a filtration fraction (FF) of 25%. Serum analysis reveals a creatinine level of 0.9 mg/dL and an elevated hematocrit of 0.6. Which of the following is the best estimate of this patient’s renal blood flow?

QID: 101023
1

400 mL/min

24%

(24/98)

2

600 mL/min

10%

(10/98)

3

800 mL/min

10%

(10/98)

4

1.0 L/min

40%

(39/98)

5

1.2 L/min

9%

(9/98)

M 1 E

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(M1.RL.12.20) Activation of the renin-angiotensin-aldosterone system yields a significant physiological effect on renal blood flow and filtration. Which of the following is most likely to occur in response to increased levels of Angiotensin-II?

QID: 100974
1

Increased renal plasma flow, decreased filtration fraction

9%

(4/46)

2

Increased renal plasma flow, increased filtration fraction

28%

(13/46)

3

Decreased renal plasma flow, decreased filtration fraction

2%

(1/46)

4

Decreased renal plasma flow, increased filtration fraction

57%

(26/46)

5

Decreased renal plasma flow, increased glomerular capillary oncotic pressure

2%

(1/46)

M 1 D

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Evidence (7)
EXPERT COMMENTS (16)
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