Lecture 04 - Quantification of Kidney Function

Lecture 04 - Quantification of Kidney Function - Q...

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Quantification of Kidney Function - Filtration : The process by which water and solutes in the blood leave the vascular system through the filtration barrier and enter Bowman’s space. - Secretion : The process of moving a substance into the tubular lumen from the renal tubular epithelial cells. (rather than through glomerulas - Reabsorption : The process of moving a substance from the tubular lumen into the renal tubular epithelial cell. (metabolized or release into vasculature) - Excretion : Exit of a substance from the body. (We focus on renal excretion here). Clearance Rate - Clearance rate: The rate at which a substance is cleared from the body . o The volume of plasma that is entirely cleared of the substance per unit time - Potential Units for Clearance Rate: o Amounts of Units/time cleared from the body (eg. gram/day ) o Time it takes for the plasma concentration of a substance to be half of its previous value (T ½ - eg. minutes). More useful when you give a substance o Volume of plasma per unit time from which all of a substance is removed (eg. ml/min). - In terms of kidney function, we measure some substance An example: Inulin Clearance to Estimate Glomerular Filtration Rate - The Clinical Problem - Almost anything that damages the kidney will ultimately result in a loss of glomerular filtration rate (GFR). - Its extremely useful to be able to measure and monitor GFR in clinical settings. o Kidney damage during surgery. o Kidney damage from toxic substances (meds). o Evaluating trajectory of kidney function loss over time (eg. days [icu], years [diabetes]). o Dosing of drugs that are cleared by the kidney (decrease kidney function you would use lower dose of the drug) Deduction of Normal Glomerular Filtration Rate - Typical renal blood flow is 1.1L/min o ~20% of cardiac output - Hematocrit is ~45%; 55% is plasma. - Renal plasma flow : (fluid carrying the blood not including the blood cells) o 1.1L/min * 0.55 = 600 ml/min - The glomerular filtration fraction is ~20% (80% would go on and return to renal vein) - So the glomerular filtration rate (GFR): o 600ml/min*(0.20) = 120 ml/min - What does this mean??? – the 120 ml/min - What does glomerular filtration mean? o We can find the volume that is total cleared of the substance that would result in the same ratio as before (i.e. before it was 10/10ml after it was 8/10ml you will move it over so that it will be 10/10 thus 8/8 would be = to 10/10, leaving 2ml/min cleared! Inulin
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Lecture 04 - Quantification of Kidney Function - Q...

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