1. Define Glomerular Filtration Rate
   1. as in other capillaries, the GFR is determined by
      1. 1. balance of hydrostatic and colloid osmotic forces acting across the capillary membrane
      2. 2. the capillary filtration coefficient (Kf)
         1. = product of permeability and filtering surface area of capillaries
   2. GFR /glomerular filtration has much higher rate of filtration the most capillaries
      1. because of high hydrostatic pressure
      2. large Kf
   3. GFR is usually 125ml/min or 180L/day
   4. filtration fraction = GFR/Renal plasma flow
      1. = 0.2
      2. ie 20% of plasma flowing through kidney is filtered through glomerular capillaries
      3. GFR = Renal plasma flow x filtration fraction
   5. GFR determined by...
      1. sum of hydrostatic and colloid osmotic forces across the glomerular membrane
         1. gives net filtration pressure
      2. glomerular capillary filtration coefficient
      3. IE. GFR = Kf x Net filtration pressure
2. Discuss the effect of afferent and efferent arteriolar constriction on GFR
   1. increased glomerular capillary filtration coefficient increases GFR
      1. changes in Kf probably do not provide a primary mechanism for the normal day-to-day regulation of GFR
      2. some disease lower Kf by reducing the number of functional glomerular capillaries
         1. thereby reducing the surface area for filtration
      3. some diseases lower Kf by increasing the thickness of the glomerular capillary membrane and reducing its hydraulic conductivity
      4. eg chronic, uncontrolled hypertension and diabetes mellitus gradually reduce Kf by increasing thickness of glomerular capillary basement membrane and, eventually, by damaging the capillaries so severely that there is loss of capillary function
   2. increased Bowman's Capsule hydrostatic pressure decreases GFR
      1. do not serve as a primary means for regulating GFR
      2. obstruction of urinary tract
         1. Bowman's capsule pressure can increase markedly, causing serious reduction of GFR
   3. increased glomerular capillary colloid osmotic pressure decreases GFR
      1. as blood passes from afferent arteriole through glomerular capillaries to the efferent arterioles...
         1. the plasma protein concentration increases about 20%
         2. because 20% of fluid in capillaries filters into Bowman's capsule
      2. two factors that influence glomerular capillary colloid osmotic pressure:
         1. arterial plasma colloid osmotic pressure
         2. the fraction of plasma filtered by glomerular capillaries
            1. increasing the filtration fraction also concentrates the plasma proteins and raises the glomerular colloid osmotic pressure