| 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 |
