Solve example questions part EXTRA CREDIT: Caleulating Glomerular Filtration Rat

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Solve example questions part EXTRA CREDIT: Caleulating Glomerular Filtration Rate (GFR) and Renal Plasma Clearance (RPC) Background Tunction of the invasively. One method of calculating GFR is to Glomerular Fitration Rate (GFR): Glomerular filtration rate is used to assess the kidney. Although GFR is a valuable piece of information, it is difficult to measure non- determine the rate of excretion (clearance) of a substance called inulin. Inulin is a plant polysaccharide that when injected intravenously , is filtered but not reabsorbed nor secreted injected intravenously and the patient's urine is collected for a specific period in the nephron. To calculate the GFR, a known quantity of inulin (N) is rate of urine formation (m/min). The urine inulin concentration is measured (mg/ml). Then a of time to calculate the blood sample is taken, and the plasma concentration of inulin is measured. The two inulin measurements (urine and plasma) are then used to calculate how much plasma must have been filtered (approximates the GFR) to produce the measured amount of urine according to the formula: GFRV hanve bee fitered lopproasinates Where: GFR V glomerular filtration rate (ml/min) rate of urine formation (ml/min) U = inulin concentration in urine (mg/ml) P- inulin concentration in plasma (mg/ml) Renal PlasmaClearance (RPC): RPC measures the rate at which a substance is eliminated from the body (ml/min). RPC is calculated by the formula: RPC Where: RPC-renal plasma clearance (ml/min) V = urine volume (ml/min) U urine concentration of substance "x" (mg/ml) plasma concentration of substance "X” (mg/ml) Renal elimination of medications: Is it filtered, absorbed, or secreted? GFR and RPC may be used together to try to understand the mechanism by which a substance a. Calculate GFR using the inulin clearance method: you are determining how much b. Calculate the RPC of "x": you are determining how much plasma should have been c. Compare the calculated GFR to the measured RPC of"x". If it is being cleared than (e.g.: a drug) is eliminated by the kidney. The steps in this process are as follows: plasma must have been filtered to make this much urine. filtered to collect this quantity of"x" in the urine can be accounted for by GFR, then "x" is being actively secreted by the nephron. Example questions: (show your work on the back of this page) 1. Calculate GFR when: V -2.5 m/min, U 35 mg/ml; P-0.6 mg/ml 2. Calculate RPC when: V-2.5 mlmin; U-30 mg/ml of "X"; P = 0.45 mg/ml of"X". 3. Is substance X being filtered only, reabsorbed, or secreted? (Circle one).

Explanation / Answer

V= 2.5 ml/min, U= 35 mg/ml, P= 0.6 mg/ml

So, GFR= 2.5 X 35/0.6 = 2.5 X 58.33= 145.825 ml/min

2. RPC= V X U/P

V= 2.5 ml/min, U= 30 mg/ml, P= 0.45 mg/ml

So, RPC = 2.5 X 30/0.45 = 2.5 X 66.67 = 166.675 ml/min

3. The substance ‘x’ is being secreted. Since RPC is greater than GFR, it indicates that the substance is actively secreted by the nephrons.

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