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Renal Function and Clearance: Understanding Kidney Physiology

Learn about renal function and clearance principles, measures of kidney function, disease classification, clinical measures, GFR estimation, and renal handling of substances. Explore key concepts and calculations in renal physiology.

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Renal Function and Clearance: Understanding Kidney Physiology

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  1. Renal Function and Clearance Whole Kidney Vocabulary Nephron Vocabulary Renal Blood Flow Renal Plasma Flow Glomerular Filtration Rate Tubular load Urinary excretion

  2. Renal 2: Learning Objectives • Explain the clearance principle. Use the clearance equation and an appropriate compound to estimate the glomerular filtration rate, renal plasma flow, and renal blood flow. • Distinguish between the use of inulin and creatinine clearances as measures of the glomerular filtration rate • Differentiate the mechanisms (filtration, secretion, reabsorption) by which compounds appear in the urine • Given plasma concentrations of a compound, calculate typical values for renal delivery and tubular load

  3. FUNCTIONS OF THE KIDNEYS • Remove nitrogenous wastes from protein metabolism. • Regulate volume and composition of ECF. • Acid-Base Balance. • Blood pressure regulation. • Removal of drugs and other foreign substances. • Release erythropoietin to control RBC production. • Convert precursor into active vitamin D3.

  4. Guide to renal disease classification • Pre-renal Causes • Cardiovascular • Endocrine disorders • Glomerular Diseases • Filtration at glomerular capillaries, • Reabsorption at peritubular capillaries • Tubular/Interstitial Diseases • Epithelial transport • Post-renal Causes • Ureter, bladder, urethra, micturition reflex

  5. Clinical Measures of Renal Function • Plasma creatinine and urea (BUN) • Clearance estimates of GFR and RPF • Fractional Excretion of Na • Micturition • Urine volume • Urine composition

  6. If plasma creatinine increases from 1 to 2 mg%, what change in GFR (normal 120 ml/min) occurred? • Increase to 300 ml/min • Increase to 240 ml/min • Increase to 180 ml/min • Decrease to 90 ml/min • Decrease to 60 ml/min • Decrease to 30 ml/min

  7. Clearance A flow of plasma from which a substance is completely removed by the kidneys Cx = Ux V = Volume/Time eg. ml/min or L/day Px Where V = urine flow; Ux = urine concentration of X; Px = plasma concentration of X; Cx = clearance of X

  8. Measurement of GFR (Inulin M.W. = 5,000) Freely Filtered Not Metabolized Not Reabsorbed Does Not Change GFR Not Secreted Not Produced Amount Filtered = Amount Excreted GFR · PIN = V ·UIN GFR = V ·UIN = CIN PIN

  9. RPF = (CPAH) 0.9

  10. Free Water Clearance The amount of water that has been added to or removed from an isotonic solution to result in the urine osmolarity Positive free water clearance = dilute urine Negative free water clearance = concentrated urine Free water clearance estimated from Urine : Plasma osmolarity U/P ratio

  11. Think, Stare, ShareFiltered, reabsorbed, secreted, excreted? Assume RPF = 625 ml/min, GFR = 125 ml/min, urine = 1 ml/min

  12. Renal Function Problem Assume RPF = 625 ml/min, GFR = 125 ml/min, urine production 1 ml/min Filt, reabs glucose Not filtered, protein Filt, reabs Na Filtered creatinine Filt, secr Penicillin

  13. What percentage of filtered water (GFR) is normally excreted in the urine? • 20% • 10% • 1% • 0.1%

  14. What percentage of filtered sodium load is normally excreted in the urine? • 20% • 10% • 1% • 0.1%

  15. Renal Handling of Salt Filtration Excretion 6 g 1,500 g Fractional excretion of Na typically < 1% If renal tubules damaged, FENa > 2%

  16. Renal Oxygen Consumption:

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