kidney

kidney

Peshawar Medical College NWFP Pakistan URINE FORMATION Peshawar Medical College NWFP Pakistan

kidney.lecture 5b 19 February 2019 dr.rashid mahmood

Glomerular Filtrate Plasma minus plasma proteins + protein bound substances

kidney.lecture 5b 19 February 2019 Definition of GFR Quantity of Glomerular Filtrate formed each Minute in all nephrons of both kidneys kidney dr.rashid mahmood

Calculation Of GFR GFR= Filtration fraction x renal plasma flow GFR= Permeability coefficient x NFP

GFR Contd…….. = 20 % of Plasma flow i.e. Filtration Fraction = 0.2 kidney.lecture 5b 19 February 2019 GFR Contd…….. = 20 % of Plasma flow i.e. Filtration Fraction = 0.2 i.e. GFR= Filtration Fraction × Renal Plasma Flow = 125 ml/min = 180 l/day kidney dr.rashid mahmood

kidney.lecture 5b 19 February 2019 kidney dr.rashid mahmood

Filtration Pressures PG= Glomerular Hydrostatic Pressure kidney.lecture 5b 19 February 2019 Filtration Pressures PG= Glomerular Hydrostatic Pressure PB= Hydrostatic Pressure in Bowman’s Capsule G= Colloid Osmotic Pressure in Glomerular Capillaries B= Colloid Osmotic Pressure in Bowman’s Capsule kidney dr.rashid mahmood

Pf = PG - PB - π G + π B = 60 – 18 - 32 + 0 = 10 mmHg kidney.lecture 5b 19 February 2019 Pf = PG - PB - π G + π B = 60 – 18 - 32 + 0 = 10 mmHg kidney dr.rashid mahmood

P f = Sum of Hydrostatic and Colloid Osmotic Forces kidney.lecture 5b 19 February 2019 GFR= Kf × P f P f = Sum of Hydrostatic and Colloid Osmotic Forces Kf = Permeability Co-Efficient = Permeability × Surface Area kidney dr.rashid mahmood

Determinants of GFR Factors affecting GFR kidney.lecture 5b 19 February 2019 Determinants of GFR Factors affecting GFR dr.rashid mahmood

Factors affecting GFR Any factor that affects determinants of GFR will affect GFR i.e. factors affecting are Filtration Co-Efficient ( Kf ) Net Filtration Pressure ( Pf ) Hydrostatic Pressure in Bowman’s Capsule Colloid Osmotic Pressure in Glomerular Capillaries Glomerular Hydrostatic Pressure Colloid Osmotic Pressure in Bowman’s Capsule Filtration Fraction Renal Plasma Flow / Blood Flow Dietary Factors kidney

1. Permeability Co-Efficient Kf = Permeability Co-Efficient = Permeability × Surface Area =12.5 ml/min/mmHg of filtration pressure (400 times that of other body capillaries) ↑ Kf → ↑GFR (and vice versa) Diseases 1.Hypertension and diabetes mellitus → ↑thickness of glomerular capillary basement membrane →↓GFR 2. Renal diseases kidney

2. Net Filtration Pressure ( Pf ) Hydrostatic Pressure in Bowman’s Capsule ↑PB → ↓ GFR (and vice versa) Obstruction of urinary tract (kidney stones) kidney

2. Net Filtration Pressure ( Pf ) Colloid Osmotic Pressure in Glomerular Capillaries Increase  G → Decrease GFR (and vice versa) 1. Arterial plasma colloidal osmotic pressure. 2. Fraction of plasma filtered. kidney

2. Net Filtration Pressure ( Pf ) Glomerular Hydrostatic Pressure ↑PG →↑GFR Primary means for regulation of GFR Factors affecting PG Arterial pressure Afferent arteriolar resistance Efferent arteriolar resistance kidney

2. Net Filtration Pressure ( Pf ) Colloid Osmotic Pressure in Bowman’s Capsule Normally little roll May ↑in renal diseases kidney

Effect of filtration fraction on GFR Increase filtration factor concentrates the plasma proteins increases glomerular colloidal osmotic pressure decreases GFR kidney

Renal Plasma flow or blood flow Increase RPF/ Blood flow Increases GFR Decrease RPF/ Blood flow Decreases GFR kidney

Dietary Factors High protein intake = RBF GFR Blood glucose = RBF GFR kidney

kidney