Phys: Test 3. Lecture 15. Measuring Clearance And Transport

Front 1

1. What is clearance

Back 1

a. Volume of plasma cleared of a substance per unit time
b. VOLUME PER TIME

Front 2

2. If you know GFR and the clearance of a substance, then what can any difference btw GFR and clearance tell you

Back 2

something about NET secretion or reabsorption

Front 3

3. CLx=?

(renal clearance)

Back 3

a. (Ux x V)/Px
b. Units are ml/minute
c. Ux= concentration of x in urine
d. V=volume of urine/time
e. Px=plasma conc of X

Front 4

4. If urine Na is 810 mEq/L plasma Na is 138 mEq/L and urine flow is 1 ml/min what is the clearance of Na?

Back 4

a. CL(Na)=
i. (810x1)/(138)
ii. 5.9

Front 5

5. If substance X is filtered and completely reabsorbed what is the clearance of X?

Back 5

zero

Front 6

6. What is the classic indicator for GFR?

Back 6

a. Clearance of inulin

Front 7

7. Freely filtered means?

Back 7

a. Concentration of X in Bowman’s capsule is same as that in the blood plasma

Front 8

8. What makes inulin a good indicator of GFR? (4)

Back 8

a. Freely filtered
b. Not reabsorbed
c. Not secreted
d. Not metabolized or produced

Front 9

9. What is the definition of GFR again? and teh equation

Back 9

a. GFR=Kf x NFP
b. Volume of filtrate formed per unit

Front 10

10. If something is freely filtered and is not reabsorbed what is the relationship between the amount in the urine and the amount filtered?

Back 10

they are the same

Front 11

11. What is the classic clearance equation?

Back 11

a. GFR= Ux x V/Px

Front 12

12. Can something have a clearance that is greater than GFR?

Back 12

a. Yes! True for a substance that is freely filtered and secreted

Front 13

13. What is a classic measure of renal plasma flow?

Back 13

a. PAH (p-aminohippurate)
b. At low concentrations, it is so avidly secreted that none of it appears in renal vein

Front 14

14. How do you mathematically show something that is highly secreted to the point that it doesn’t appear in the renal vein? Consider this with PAH

Back 14

a. Arterial input=venous output + urine output
i. But in the case of PAH venous output is zero

so arterial input equals urine output

Front 15

15. If you measure the clearance of inulin what will that give you

Back 15

GFR

Front 16

16. If you measure the clearance of PAH what will you get a measure of?

Back 16

renal plasma flow

Front 17

17. If clearance of substance equals GFR what has happened to NET reabsorption or secretion?

Back 17

a. No net reabsorption or secretion

Front 18

18. If clearance < GFR there has been net....?

Back 18

a. Reabsorption

Front 19

19. If clearance > GFR, there has been net what?

Back 19

a. Secretion

Front 20

20. Why use creatinine to measure GFR?

Back 20

a. It acts like inulin
b. It is not reabsorbed and only a very small amount is secreted
i. This means it kind of overestimates GFR
1. But the colormetric test used overestimates plasma creatine, thus they balance each other out and can measure GFR

Front 21

21. Is creatine clearance dependent or independent of urine flow

Back 21

a. Independent of urine flow

Front 22

a. Independent of urine flow

Back 22

a. CL= (UxV)/(Cp)

Front 23

23. What happens to CrCl (creatinine clearance) if there are changes in muscle mass

Back 23

a. Different ages will have different muscle masses
i. Thus young/old will have low muscle mass which gives lower CrCl values which can make GFR look low
1. But remember old folks will have a general decrease in GFR that is not just due to their lower muscle mass

Front 24

24. How are plasma creatinine and GFR related?

Back 24

a. Inversely
b. If GFR is low, you can’t get rid of it, so the blood level of creatinine will go up

Front 25

26. What is BUN?

Back 25

blood urea nitrogen

Front 26

Why is BUN important?

Back 26

a. It can be used as an estimate of GFR
b. Because blood urea nitrogen is handled by filtration
i. But it also deals with reabsorption and secretion
ii. Thus is flow dependent
iii. And not perfect for GFR readings

Front 27

28. Does Renal urea reabsorption depend on urine flow?

Back 27

Yes, making it not a perfect estimate for GFR

Front 28

29. With low urine flow is more or less urea absorbed? What will this do to BUN?

Back 28

a. More is absorbed
b. Thus more is in the blood
c. High BUN

Front 29

During volume depletion, what happens to urea excretion? BUN?

Back 29

You have a urine flow depression, thus urea excretion drops, and it is instead absorbed.

this leads to high BUN

Front 30

31. Is urea production constant?

Back 30

No

Front 31

32. With a high protein diet or enhanced tissue breakdown, what happens to urea production and BUN?

Back 31

a. Urea production and BUN increase

Front 32

33. If a patient has low protein diet or LIVER DISEASE what happens to urea and BUN?

Back 32

a. Urea production is down, so BUN is down

Front 33

34. Flitered load=?

Back 33

a. GFR x Cp

Front 34

35. Excretion Rate

Back 34

U x Vdot

urine conc. x flow rate of urine

Front 35

36. Amount excreted= ?

Back 35

a. Amount filtered - amount reabsorbed + amount secreted

Front 36

37. Filtration fraction=?

Back 36

a. GFR/RBF

Front 37

38. Increased FF does what to Bowman’s capsule

Back 37

a. Increased fluid in Bowman’s Capsule

Front 38

40. If you decrease FF what does this mean for Bowman's capsule?

Back 38

a. LESS fluid into Bowman’s capsule

Front 39

41. What will decreased FF do to oncotic pressure in the peritubular capillaries?

Back 39

a. Decrease it

Front 40

With low flow, will urea absorption be increased or decreased?

Back 40

increased