The kidney is very important organ

It supplied about 20 % of cardiac outputCardiac output is about 72 ml per peat, 72 peat per min average 5200 ml per minuteRenal blood flow is about 1-1.2 L/min enter the kidney, most of it 90 % goes to the cortexRenal plasma flow equal Renal blood flow (1 – Ht), it is about 500 – 600 mL/miGlomerular filtration rate equal About 20 % of Renal blood flow (filtration fraction) 100 – 120 mL/minThe kidneys maintains semi constant glomerular filtration rate by some mechanisms here illustration

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 vasodilationModerate efferent arteriole vasoconstriction(1).

Decreased By: (decrease GFR)

Afferent arteriole vasoconstrictionEfferent 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)

DehydrationDecrease renal blood flowSevere efferent vasoconstriction

Decreased by: (increase GFR)

Hypoproteinemiaincrease renal blood flow

Autoregulation of GFR and Renal Blood Flow

Effective in blood pressure range from 75 to 160 mmHgdrop blood pressure below 75 or higher than 160 will change GFR about 10 percent mechanismhigh blood pressure lead to afferent arteriole constriction and dilatation the efferent arteriolelow blood pressure, dilatation afferent arteriole and constriction efferent arteriole