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Phys3 Clear & Transp
| Question | Answer |
|---|---|
| Clearance | Volume of plasma cleared of a substance per unit time |
| What does clearance asses | 1.Filtration. 2.reabsorption. 3.secretion. **The amount cleared equals the amount in the urine at that time. |
| What does a difference b/w GFR and the clearance of a substance indicate? | NET secretion or reabsorption |
| Cx X Px = Ux X V | 1.Cx: volume of plasma cleared per unit time. 2.Px: Plasma concentration of x. 3.Ux: [x] in urine. 4.V: volume of urine per time. |
| Clearance equation | Cx = (Ux X V)/Px **Measured in ml/min, measure the VOLUME of plasma cleared per unit TIME |
| If a substance is filtered and COMPLETELY reabsorbed, what is the clearance of that substance? | O |
| What does it mean to be freely filtered and what are some examples of freely filtered substances? | Concentrations in Bowman's capsule equal that in the BL plasma. 1.Univalent electrolytes. 2.Urea. 3.Glucose. 4.aa's. **GFR=(Ux X V)/Px |
| What are some examples of solutes that are not freely filtered? | those bound to proteins: 1.Ca2+. 2.Phosphate. 3.Magnesium. |
| Why is inulin a good indicator of GFR | 1.Freely filtered. 2.Not reabsorbed. 3.Not secreted. 4.Not Metabolized. **C(inulin) will equal GFR |
| Can a substance have a clearance that is greater than GFR? | YES, if the substance is freely filtered AND is excreted. |
| Can the clearance of a substance be used to measure RBF? | YES, if it is secreted and NONE appears in the renal vein. **RBF = (U(PAH) X V)/P(PAH) |
| substance with a clearance = RBF | PAH (b/c it can be removed in a single pass). |
| If GFR=Clearance | NO net reabsorption or secretion. |
| If GFR < Clearance | Net SECRETION |
| If GFR > Clearance | Net Reabsorption |
| Practical method of measuring GFR | Creatinine clearance. It is endogenous and is exported into the BL continuously by skeletal muscle. **It is freely filtered and not reabsorbed (very little is secreted so it could overestimate GFR). |
| Method for measuring creatine clearance | 1.24 hr patient urine. 2.BL sample during collection time. 3.[creatinine] in both BL & urine. 4.Use clearance formlua. |
| Can C(creatinine) levels give inaccurate GFR? | YES: 1.Dec muscle mass (elderly and children will appear to have dec GFR). 2.Ingestion of large amount of meat (Inc [creatinine] which will make GFR appear high). |
| What happens to teh GFR with aging? | It DECREASES with every DECADE |
| normal plasma value of creatinine? | 1mg/dl |
| relationship b/w plasma creatinine and GFR? | INVERSELY related. **If GFR dramatically decreases, plasma [creatinine] Inc (GFR < 40ml/min) |
| How will renal disease cause Inc in BUN? | Low GFR leads to low urine flow, which Inc urea retention and INCREASES BUN. **Fast flow rates will lead to decreased BUN |
| using BUN to determine dehydration | High BUN confirms dehydration. The volume depletion causes low GFR and very low urea excretion. **Problematic b/c High protein diet causes Inc BUN while low protein diet causes dec BUN. |
| what happens to the BUN/Creatine ratio with vloume depletion? | INCREASES b/c of the flow dependence of urea excretion but NOT creatinine. |
| How does an Inc FF affect π(PTC) | INCREASES it |
| How does a Ded FF affect π(PTC) | DECREASES it |
Created by:
WeeG
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