Lisa M. Harrison-Bernard, PhD 5/10/2011
Renal Physiology 2011 Lisa M. Harrison-Bernard, PhD [email protected] Renal Problem Set Review
Approximate Water Distribution 70 Kg Adult Human • Total Body Water (TBW) ~ 60% Body Weight (BW) =~= ~ 42 L • Intracellular Fluid (ICF) ~ 40% BW = ~ 25 L • Extracellular Fluid (ECF) ~ 20% BW = ~ 17 L “ 20, 40, 60 ” rule of thumb
LSU Medical Physiology 2011 1 Lisa M. Harrison-Bernard, PhD 5/10/2011
Total Body Water (TBW) = 0.6 X Body Weight = 42 L
EtExtracell lllular Intracellular Fluid (ICF) Fluid (ECF) 1/3 of TBW 2/3 of TBW Cell membrane Interstitial Fluid 3/4 of ECF = Plasma ¼ of ECF
Capillary membrane
Osmotic EQ Across Membrane
Solutes Solutes (don’t move) (don’t move)
H20 (moves) H20 (moves)
WtWater diff uses across semiblipermeable cell membranes = water channels = Aquaporins Net movement water = osmotic EQ
LSU Medical Physiology 2011 2 Lisa M. Harrison-Bernard, PhD 5/10/2011
Determination Body Fluid Volumes - Indicators TBW ECV BV PV
D2O Inulin Radio- RISA deterium- active radioiodinated heavy water Iron serum albumin 131I-Albumin HTO Mannitol Cr51 T-1824 Evan’s tritium, RBC Blue dye, tritiated water bound to albumin Radioactive Sodium 22Na
Indicator Dilution Principle
Mix
Indicator Measure Conc at Known EQ Amount (measurable) ? V ?
Amount of Indicator = Volume X Conc of Indicator V = Amount / Conc of Indicator Conc = Amount / Volume of Distribution
LSU Medical Physiology 2011 3 Lisa M. Harrison-Bernard, PhD 5/10/2011
Glomerular Ultrafiltration - Eq 3-10
GFR = Kf [(PGC-PBS) - (GC-BS)]
PUF Rate of glomerular ultrafiltration =
ultrafiltration coefficient (Kf) X
net Starling forces (PUF)
Clearance S =
Mass S excreted / time
GFR: Plasma [S] Inulin • Creatinine ClS • PS = US • V RPF: • PAH ClS =U= US • V
PS
LSU Medical Physiology 2011 4 Lisa M. Harrison-Bernard, PhD 5/10/2011
YOU DO NOT NEED TO MEMORIZE THESE FORMULAS Current Recommendations for Routine Estimation of GFR in Clinical Setting
MDRD Study Equation:
GFR (ml/min/1.73 m2) =
-1.154 -0.203 175 X (SCr) X (Age) X (0.742 if female) X (1.212 if African American)
Cockcroft-Gault Equation:
Clearance Cr (ml/min) =
(140 – age) X (Wt in kg) X (0.85 if female) / (72 X SCr)
Renal Parameters
• Renal Fraction (RF) = RBF/CO =
1,000 ml/min 5,000 ml/min = 0.20 = 20% • Hematocrit (Hct) = 0.40
40% BV = RBC
60% BV = Plasma
LSU Medical Physiology 2011 5 Lisa M. Harrison-Bernard, PhD 5/10/2011
Renal Parameters • Renal Plasma Flow (RPF) =
RBF x (1 – Hct)
1,000 ml/min x (1 – 0.40) = 600 ml/min
• Filtration Fraction (FF) = GFR RPF = 125 ml/min 600 ml/min = 0.20
Renal Parameters • • Urine flow (V) = 1 ml/min
• • Fluid reabsorbed = (GFR – V)
125 ml/min – 1 ml/min = 124 ml/min > 99%
* Fluid Filtration >>> Urine Output *
LSU Medical Physiology 2011 6 Lisa M. Harrison-Bernard, PhD 5/10/2011
Substance A • Filtered Load GFR X Plasma [A]
GFR • PA • Excretion Rate Urine [A] X Urine flow • UA • V
The End
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