Renal Plasma Clearance

Question 1

Define clearnace & state its equation

Answer 1

It is the volume of plasma in ml cleared or cleaned of a particular substance by kidneys per minute
Cx=Ux*V/Px

Question 2

Inulin clearnace is equal to…….while PAH clearnce is equal to……

Answer 2

GFR
ERPF

Question 3

The subtance with C more than glucose but lower than inulin is……., while that having C more than inulin but lower than PAH is…….

Answer 3

Urea (70 ml/min)
Creatinin

Question 4

Describe significance of determination of plasma clearance

Answer 4

1. Study mode of handling of different solutes in the filtrate
2. Measure GFR by inulin
3. Measure RPF by PAH
4. Calculate filtration fraction from 2 & 3

Question 5

Mention criteria for substance used to measure GFR

Answer 5

1. Freely filtered
2. Not reabsorbed or secreted
3. Not metabolized or synthesized in tubule
4. Not stored in kidney
5. Non-toxic & physiologically inert
6. Not bound to PPs
7. Easy to measure in urine & plasma
8. Has no effect on filtration rate

Question 6

Mention disadvatantages of using inulin clearance

Answer 6

1. Time consuming & difficult as it needs continuous infusion
2. It is not a natural substance

Question 7

List advantages of using creatinine clearnce to calculate GFR

Answer 7

1. It is a natural subtance, end-product od muscle metabolism
2. It is continuously produced by the body & its conc in plasma is normally stable
3. Plasma & urine conc can be measured by simple colorimetric method

Question 8

Mention disadvatanges of creatinine clearance measurement

Answer 8

1. Creatinine is not only filtered but also secreted in urine
2. There are errors in measuring plasma creatinine
   Howerver, both the numerator & denominator are 10% too high thus the errors cancel.

Question 9

Mention chchs of substance used to measure RPF

Answer 9

1. Freely filtered
2. Not reabsorbed
3. Completely secreted
4. Not metabolized, stored or produced by kidneys
5. Does not affect RPF
6. Its level can be easily measured

Question 10

The closest substance to measuring RPF is……but it is only…..% cleared thus the value measured is called…..=……

Answer 10

Para-aminohypyric acid
90
Effective RPF
625 ml/min

Question 11

Why is the extraction ratio of PAHA not 10.% although it is completely absent from peritubular capillaries?

Answer 11

Little blood bypass peritubukar capillaries & escape in vasa recta and in circulation to renal capsule& back to venous circulation which means that JM nephron ability to get rid of PAHA is not like the cortical nephron.

Question 12

Write the equation for actual RPF & RBF

Answer 12

-Actual RPF=ERPF/extraction ratio
-RBF=RPF/1-Hct