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205textnotes41 - i inulin injected at 100 mg/dL plasma ii...

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- the plasma concentration at which saturation occurs is called the renal threshold . ( therefore, intake of excess amounts will often be seen in urine Figure 19-15 ) - facilitated diffusion out of epithelial cell and into Interstitial Fluid - diffusion from interstitial fluid to the peritubular capillaries - urea, foreign lipid-soluble substances (DDT) - diffuse across plasma membranes of epithelial cells - concentration gradient created once water beings to be reabsorbed Excretion and Clearance: (Figure 19-16) Excretion = filtration - reabsorption + amount secreted Clearance : an abstract concept that describes how many mL of plasma passing through the kidneys have been totally cleard of a substance in a given period of time. Clearance of a substance = (urine excretion of the substance [mg/min]) / (plasma concentration of the substance [mg/mL]) where: urine excretion = (urine flow) X (urine concentration) e.g. INULIN: comes out in the filtrate and it is neither reabsorbed nor secreted.
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Unformatted text preview: i) inulin injected at 100 mg/dL plasma ii) excretion = 125 mg inulin per min. clearance = (125 mg inulin/min) / (100 mg inulin /100 mL plasma) = 125 mL plasma / min Filtration = plasma concentration X GFR therefore GFR = Filtration / plasma concentration for inulin, filtration = excretion therefore, (inulin excretion) / (plasma inulin) = GFR = clearance Inulin can therefore be used to determine GFR. This can then be used to determine filtration rates of other substances. Figure 19-17 Micturition: read section on 617-618 (Figure 19-18)-------------------------------------------------------------------------------------Chapter 20: FLUID AND ELECTROLYTE BALANCE -------------------------------------------------------------------------------------A. Water Balance and Urine Concentration -----------------------------------------------------------------------...
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