Topic 42 - Renal plasma flow (RPF), filtration fraction

Question 1

Words to include in renal plasma flow (RPF)

Answer 1

• Plasma amount flowing through the kidney (RPF)
• Flick-principle
  
  • Law of conservation of matter
  • A. renalis / arterial side
  • V. renalis / venous side
  • Urine
• Clearance of substance filtered and completely excreted (RPF)
• P-aminohippuric acid (PAH)
  
  • Filtered
  • Secreted
• A. renalis
• V. renalis
• Urine
• Secretion and reabsorption in the tubules
• The amount of matter
  
  • U x V
• Appearing on the given
  
  • Pv x RPF
• Location is one unit of time
  
  • Pa x RPF
• Pa x RPF = Pv x RPF + U x V

Question 2

Words to include in filtration fraction

Answer 2

• GFR/RPF = 120(Cin)/670(Cpah) = 0.18
• Regulation
  
  • Efferent arteriole
    
    • Adaptive contraction
  • Tubulo-glomerular feedback
• Rise of blood pressure
  
  • Afferent arteriole
    
    • Vasoconstriction
      
      • Bayliss effect
  • Efferent arteriole
    
    • Vasodilation
• Fall of blood pressure
  
  • Afferent arteriole
    
    • Vasodilation
  • Efferent arteriole
    
    • Vasoconstriction

Question 3

Renal plasma flow

Answer 3

• RPF: The volume of blood plasma delivered to the kidney per unit time
• RPF: Measures the clearance of any substance that is both filtered and completely excreted
  
  • ​Eg. P-aminohippuric acid (PAH)
• The determination of the plasma amount flowing through the kideny (RPF) is based on Flick-principle (law of conservation of matter):
  
  • ​The amount of substance entering the kidney through a. renalis per unit time, must be equal to the sum of amunts of the substances leving the kidney with v. renalis and the urine
  • A. renalis = v. renalis + urine

Question 4

Filtration fraction

Answer 4

• Filtration fraction:
  
  • The ratio of GFR to the RPF
  • ​The proportion of the fluid reaching the kidneys that passes into the renal tubules
• Filtration fraction = GFR/RPF = 12(Cin)/670(Cpah)=0.18
• GFR and RPF do not change within the wide ranges of blood pressure
  
  • This is regulated by the adaptive contraction of the efferent arteriole and the tubulo.glomerular feedback
  • Rise of blood pressure:
    
    • ​Afferent arteriole: vasoconstriction (Bayliss-effect)
    • Efferent arteriole: vasodilation
  • Drop of blood pressure:
    
    • ​Afferent arteriole: vasodilation
    • Efferent arteriole: vasoconstriction