Regarding Glomerular filtration rate (GFR) is
(Inulin clearance measure the GFR) (31 6- 18-Guy ton 11th, 643-4.5-Ganong 23rd, 302-K Sembulingam 5th). In the average adult human the GFR is about 125ml/min, 1.73 smq/cm2 or 180L/day and tubular reabsorption is 178.5 L/day, leaving 1.5L/day of fluid to be excreted in the urineGFR is about 20% of the renal plasma flowGFR = Kt (Glomerular capillary filtration coefficient) x Net filtration pressure* Renal blood flow - Average (70 kg) man the combined blood flow through both kidney is about 1100 ml/min or about 22% of cardiac out put A substance that is completely filtered but neither reabsorbed nor secreted should be used to measure the GFR i.e. - InulinMeasurement of GFR1. Inulin - clearance test - Most commonly used2. Urea - clearance test3. Cr51 - EDTA clearance test4. Endogenous creatinine clearance test (Worth while index of renal functions)**Increased glomerular capillary colloid osmotic pressure decrease GFRTwo factor that influence the glomerular capillary colloid osmotic pressure raises the glomerular capillary colloid osmotic pressure which in turn decreases GFR***1. Arterial plasma colloid osmotic pressure (oncotic pressure). Increasing the arterial plasma, colloid osmotic pressure raises the glomerular capillary colloid osmotic pressure which in turn decreases GFR***2. Fraction of plasma filtered by the glomerular capillaries (Fdtration fraction) - Increasing the filtration fraction also concentrated the plasma proteins and raise the glomerular colloid osmotic pressure and tend to reduce GFR * Sodium, Inulin, Glucose are freely filtered across glomerular capillaries***Factors that can Decrease the GFR* Renal disease, DM. Hypertension* Urinary tract obstruction (eg kidney stones)* | Renal blood flow. Increased plasma proteins* *** | Arterial pressure (has only small effect due to auto regulation)* | Angiotensin II (drugs that block angiotensin II formation)* | Sympathetic activity. Vasoconstrictor hormones (eg Norepinephrine, epinephrine, endothelin) platelet activing factor, PGF2* Increase Bowman's capsule hydrostatic pressureFactor than can Increase the GFR* Increased glomerular capillary filtration Coefficient (Kt)* Increased glomerular capillary hydrostatic pressure* Endothelial derived Nitric oxide (NO)-| renal vascular resistance -|GFR* Prostaglandins (PGE2) Bradykinin. CAMP, Dopamine, ANP, BNP* High protein intake and increased blood glucose -| renal blood flow and GFRALSO-REMEMBER* Normal filtration fraction varies from 15-20%* Normal net filtration pressure is about 20 mmHg (varies 15-20 mmHg)* Kidney receives about 25% of cardiac out put (1.2 - 1.3 litre of blood per minute)* The tubuloglomerular feed back is mediated by - sensing NaCl concentration in the macula densa*** The prime driving force for counter current multiplier system is - Reabsorption of Na+ in thick ascending limb*** Urinary concentrating ability of the kidney is increased by(i) ECF volume contraction / water deficit(ii) High level of ADH(iii) High osmolarity of renal medullary interstitial fluid* Tc99 DTPA (Diethylene- Pentothenic Acid) is the agent of choice for assessment of GFR*** Patient having acute cardiac failure, do not show edema because there is fall in the systemic capillary hydrostatic pressure
Normal glomerular filtration rate is 625 L/day
Inulin clearance measure the GFR
| plasma oncotic pressure increases the GFR
Diabetes mellitus increases the GFR
Kidneys and Body Fluids