Glomerular filtration rate is used to assess the function of

Glomerular filtration rate is used to assess the function of the kidney. Although GFR is a valuable piece of information, it is difficult to measure non-invasively. One method of calculating GFR is to determine the rate of excretion (clearance) of a substance called is a plant polysaccharide that when injected intravenously, is filtered but not reabsorbed nor secreted in the. To calculate tire GFR, a known quantity of (N) is injected intravenously and the patient\'s urine is collected for a specific period of time to calculate the rate of urine formation (ml/min). The urine concentration is measured (mg/ml). Then a blood sample is taken, and the plasma concentration of is measured. The two 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: GFR = V Times U/P Where: GFR = filtration rate (ml/min) V = rate of urine formation (ml/min) concentration in urine (mg/ml) concentration in plasma (mg/ml) RPC measures the rate at which a substance is eliminated from the body (ml/min). RPC is calculated by the formula: RPC = V Times U/P Where: RPC = renal plasma clearance (ml/min) V = urine volume (ml/min) U = urine concentration of substance \"x\" (mg/ml) P = plasma concentration of substance \"x\" (mg/ml) Is it filtered, absorbed, or secreted? GFR and RPC may be used together to try to understand the mechanism by which a substance (e.g.: a drug) is eliminated by the kidney. The steps in this process are as follows: a. Calculate GFR using the clearance method: you are determining how much plasma must have been filtered to make this much urine. b. Calculate the RPC of \"x\": you are determining how much plasma should have been filtered to collect this quantity of \"x\" in the urine c. Compare the calculated GFR to the measured RPC of \"x\". If it is being cleared than can be accounted for by GFR, then \"x\" is being actively secreted by the. 1. Calculate GFR when: V = 2.5 ml/min; U = 35 mg/ml; P=0.6 mg/ml 2. Calculate RPC when: V = 2.5 ml/min; 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).

Solution

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

As per the formula:

GFR=V*U/P=2.5*(35/0.6)=2.5*58.33=145.83

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

As per the formula:

RPC=V*U/P=2.5*(30/0.45)=2.5*66.67=166.67

3) Since RPC value is greater than GFR (166.67>145.83) I think the drug is reabsorbed by nephron.