The kidney is very important organ

  • It supplied about 20 % of cardiac output
  • Cardiac output is about 72 ml per peat, 72 peat per min average 5200 ml per minute
  • Renal blood flow is about 1-1.2 L/min enter the kidney, most of it 90 % goes to the cortex
  • Renal plasma flow equal Renal blood flow (1 - Ht), it is about 500 - 600 mL/mi
  • Glomerular filtration rate equal About 20 % of Renal blood flow (filtration fraction) 100 - 120 mL/min
  • The kidneys maintains semi constant glomerular filtration rate by some mechanisms here illustration
    jfr pressure.jpg

    Glomerular filtration rate depend on:

    1. Pressure gradient across the filtration barrier:

      • glomerular hydrostatic pressure (= 60 mmHg). It promotes filtration.
      • hydrostatic pressure in Bowman’s capsule (= 18 mmHg). It opposes filtration.
      • colloid osmotic pressure of glomerular plasma proteins (= 32 mmHg). It opposes filtration.
      • Net Filtration Pressure (NFP) = 60-18-32= 10 mmHg.
    2. Permeability of the filtration barrier (through 3 layers):

      • The endothelium of capillary
      • Filtration slits of epithelial lining of bowman capsule (Podocytes)
      • Basement membrane (high negatively charge due to presence of proteoglycans)
    3. Filtration membrane surface area

    * Effect of glomerular hydrostatic pressure

    Increased by: (increase GFR)

  • increase Arterial blood pressure (slightly affect due to autoregulation)
  • Afferent arteriole vasodilation
  • Moderate efferent arteriole vasoconstriction(1).

    Decreased By: (decrease GFR)

  • Afferent arteriole vasoconstriction
  • Efferent arteriole vasodilation

    * Effect of hydrostatic pressure in Bowman’s capsule

    Increased by: (decrease GFR)

  • Urinary obstruction (such as: Kidney stones)
  • Kidney edema

    * Effect of colloid osmotic pressure of glomerular plasma proteins

    Increased by: (decrease GFR)

  • Dehydration
  • Decrease renal blood flow
  • Severe efferent vasoconstriction

    Decreased by: (increase GFR)

  • Hypoproteinemia
  • increase renal blood flow

    Autoregulation of GFR and Renal Blood Flow

  • Effective in blood pressure range from 75 to 160 mmHg
  • drop blood pressure below 75 or higher than 160 will change GFR about 10 percent mechanism
  • high blood pressure lead to afferent arteriole constriction and dilatation the efferent arteriole
  • low blood pressure, dilatation afferent arteriole and constriction efferent arteriole