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بسم هللا الرحمن الرحيم ﴿و ما أوتيتم من العلم إال قليال﴾ صدق هللا العظيم االسراء اية 58 By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology • • • • • • • • • • Given these structures: 1. basement membrane 2. fenestra 3. filtration slit Choose the arrangement that lists the structures in the order a molecule of glucose encounters them as the glucose passes through the filtration membrane to enter Bowman’s capsule. a. 1,2,3 b. 2,1,3 c. 2,3,1 d. 3,1,2 e. 3,2,1 Def., • Means the bulk flow of a solvent through a filter carrying with it the solutes that are small enough to pass through the filter. Blood Capillary endothelium Basement Membrane Podocytes slits Bowman Capsule Def., • It is an ultrafiltration since it is plasma minus plasma protein and cellular elements while simple filtration excludes only cellular elements. Blood Capillary endothelium Basement Membrane Podocytes slits Bowman Capsule Blood Cells Plasma proteins Plasma solutes Dynamics: • Glomerular Filtration is formed by the forces of filtration as many capillary filtrate in the body (Starling's forces of filtration). • They are 4 forces; 2 Hydrostatic pressures 2 Oncotic pressures Glomerular capillary Glomerular Hydrostatic Pressure (Gp) Glomerular Oncotic Pressure (Gπ) Capillary endothelium Basement Membrane Podocytes slits Bowman Capsule Bowman oncotic Pressure (B π) Bowman Hydrostatic Pressure (Bp) Gp = 60 mmHg Bπ = 0 mmHg Gπ = 32 mmHg Gp = 18 mmHg • GFR is determined by Starling's principle; ″The rate & direction of fluid movement is proportional to the algebraic sum of hydrostatic & oncotic pressures″ • So, GFR α (hydrostatic pressure – oncotic pressure) GFR α { (Gp- Bp) – (Gπ – Bπ)} • KF = filtration coefficient •Net filtering force {60-(32+18)} = 10 mmHg and GFR = 120 mL/ min Glomerular filtration Systemic capillary filtration Exchange 1.6 m2 – of which only 1000 m2 of systemic 2-3% are available for capillary 25%- 35% are filtration (320-480 cm2) opened 250- 350 m2 Pulmonary capillary Surface area is 60 m2. Filtration Rate 180 L/day 20 L/day are filtered at arterial end, of which 18L are reabsorbed at venous end & 2L by lymphatic. Capillary Hydrostatic 45-60 mmHg 32 mmHg at art. end & Pressure decrease to 15 mmHg at venous end Osmotic Pressure of 25 mmHg at afferent 25 mmHg along the whole Plasma Protein end of capillary & rises length to 37 mmHg at efferent end of capillary. Filtration Coefficient 4mL/min/1 mmHg/100 0.01mL/min/1mmHg/100 gm gm. Capillary Area Gπ = 25 mmHg Gp = 60 mmHg Gπ = 37 mmHg Def., • Volume of plasma filtered by both kidney per unit time Value: – 125 ml/min – 180 L/day or – 60 nl/min for single nephron (SNGFR). Filtration fraction: is part of RPF filtered in Glomeruli GFR = 125 ml/min = RPF = 1/5 or 20% 650 ml/min RPF 650 ml/min FF= 120/ 650 = 20% GFR 120 ml/min RPF 649 ml/min Urine flow rate 1 ml/min Significance of High GFR: • To ensure processing of plasma (3L) about 60 times/day (since daily GFR = 180L/day prevents accumulation of metabolites. Causes of high GFR: 1) High filtration coefficient: • KF is volume of fluid filtered /min/ mmHg pressure difference across the membrane Causes of high GFR: 1) High filtration coefficient: • For the kidney 4 ml/ min/ mmHg/ 100 gm tissue or 12 ml/ min/ mmHg/ 300gm (both kidneys). • For systemic capillary 0.01 ml/ min/ mmHg/ 100gm tissue. • This is due to high permeability of the glomerular membrane for same hydrostatic pressure gradient. Causes of high GFR: 2) High capillary hydrostatic P.: • It is about 45- 60 mmHg in glomerular capillary • In systemic capillary 32 mmHg at arterial end and 15 mmHg at venous end Causes of high GP: 1. Renal artery → short, wide, direct branch from aorta. 2. Afferent arteriole → straight branch of interlobular artery 3. Efferent arteriole → narrower than afferent arteriole 4. Glomerular capillaries →present between two arteries Causes of high GFR: 3) High RPF.: • It is about 600ml/ min. • This high RBF eventually leads to high GFR. RBF Factors Affecting GFR: Glomerular hydrostatic pressure • About 45 – 60 mmHg • Help GFR Bowman’s capsular hydrostatic pressure • About 18 mmHg • Oppose GFR Oncotic pressure of plasma protein • About 32 mmHg • Oppose GFR Renal plasma flow (RPF) Filtration coefficient • About 650 ml/min • Help GFR • About 4 ml/min/ 1mmHg/ 100 gm • Help GFR • It is high compared to systemic capillary Causes of high GP Factors affecting: A) Systemic ABP: • Between 80- 180 mmHg ( no change) • Less than 80 mmHg → ↓ Gp • More than 180 mmHg →↑ Gp B) Balance between afferent and efferent arterioles resistance • It is about 18 mmHg helps to maintain renal tubules patent. • Acts as a driving force to propel glomerular filtrate along whole length of renal tubules. • If increased e.g. in ureteric obstruction decrease GFR. Bp Increased Bp • Normally 32 mmHg. • If changed marked effect on GFR. • Increase plasma oncotic pressure decrease GFR. • As in: 1. Marked hyperproteinemia as in multiple myeloma. 2. Dehydration, hemorrhage, sever burns & chronic diarrhea. Gπ • Leakage of plasma albumin from glomerular membrane in some pathological conditions decrease plasma oncotic pressure & increase Bowman’s oncotic pressure increase GFR. • RPF affect indirectly the plasma oncotic pressure • Increase RPF maintain normal plasma oncotic pressure and filtration equilibrium is achieved too late helps GFR. • Decrease RPF elevates plasma oncotic pressure decrease GFR. High RPF • It is the effectiveness of the permeability of the barrier. • It depends on: 1. Hydraulic conductivity (water permeability of the barrier). 2. Effective filtration surface area 2. Effective filtration surface area is affected by: a. Total number of functioning glomeruli. b. State of intraglomerular mesangium. • Their contraction (e.g. by AII) decrease effective filtration area & their relaxation (e.g. by dopamine) increase effective surface area. V.D. of afferent arterioles ↑ Gp ↑ RPF FF = no change ↑ GFR V.C. of afferent arterioles ↓ Gp ↓ RPF FF = no change ↓ GFR V.D. of efferent arterioles ↓ Gp ↑ RPF FF = decrease ↓ GFR V.C. of efferent arterioles ↑ Gp ↓ RPF FF = Increase ↑ GFR Afferent Efferent RPF GFR (Preglomerular (Postglomerular resistance) resistance VC VD --- --VC VD FF (GFR / RBF) constant constant إيمحتب THANKS