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Renal Physiology > Clearance > Flashcards

Clearance Flashcards

1
Q

Define Clearance.

A

“The volume of blood or plasma that can be freed of a specified constituent in a specified time (usually one minute)

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2
Q

How are the stages chronic kidney disease determined?

A

Chronic kidney disease is staged on the basis of GFR as estimated by creatinine (GFR proportional to 1/SCr)

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3
Q

What is the definition (clinical measurement) of chronic kidney disease?

A

Chronic kidney disease = kidney damage or GFR < 60 mL/min/1.73 m for >/= 3 months

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4
Q

How is kidney damage defined?

A

Kidney damage is defined as pathologic abnormalities or markers of damage, inc. abnormalities in blood or urine tests or imaging studies.

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5
Q

What is the equation for renal clearance?

A

Cx= (Ux/Px) x V

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6
Q

What happens to inSulin in the kidney?

A

InSulin is freely filtered, reabsorbed in proximal tubule taken up by endocytosis and degraded to constituent AA –> very little in final urine

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7
Q

What happens to inulin in the kidney?

A

Inulin is freely filtered; not reabsorbed, secreted or metabolized –> all filtered ends up in the final urine

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8
Q

How do the renal clearance of Insulin and inulin compare?

A

C inS < C in

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9
Q

Under what circumstances would maximum renal clearance occur?

A

Filtratio alone is not enough, reabsorption will lower clearance
to maximize the clearance –> secrete everything else into the tubule, filtration is only a subset of what goes thru the glomerulus

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10
Q

What are the units for clearance?

A

“VOLUME per time” ex: mL/min, mL/min/kg or m2

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11
Q

What term is used to describe: “the amount of blood or plasma that has been “completely cleaned” of a substance.

A

“Clearance”

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12
Q

What term is used to describe: “the amount of substance filtered into Bowman’s space per unit time”

A

“Filtered load”

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13
Q

Define Clearance.

A

The amount of blood or plasma that has been completely cleaned of a substance

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14
Q

Define “Filtered load”

A

The amount of substance filtered into Bowmans space per unit time (an amount not a volume)

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15
Q 
Filtered load is measured as:
A. Weight
B. Weight per unit time
C. Volume
D. Volume per unit time
E. Weight per unit volume
A

B. Weight per unit time

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16
Q

What term is used to describe: “the amount of substance filtered into Bowman’s space per unit time”

A

“Filtered load”

17
Q

Define Clearance.

A

The amount of blood or plasma that has been completely cleaned of a substance

18
Q

Define “Filtered load”

A

The amount of substance filtered into Bowmans space per unit time (an amount not a volume)

19
Q 
Filtered load is measured as:
A. Weight
B. Weight per unit time
C. Volume
D. Volume per unit time
E. Weight per unit volume
A

B. Weight per unit time

20
Q

Clearance of “x” only measures GFR if…..?

A

“X” enters only as filtrate and exits only in final urine.

21
Q

Can we measure GFR using Clearance measurements?

A

Yes- as long as [X] plasma = [X] in filtrate

must remain in filtrate unchanged until final urine: no reabsorption, no secretion, no degradation while in tubules.

22
Q

What is the “gold standard” for GFR/Clearance measurements?

A

Inulin- a polysaccharide, freely filtered,

cant pass through tight jxns, no transport mechanisms, no enzymes present in tubular lumen to degrade.

23
Q

T/F creatinine is often used as a surrogate for inulin?

A

True - easier to measure, should be constant

24
Q

If GRF decreases by 50%, what happens to Serum Creatinine levels?

A

Serum Creatinine inc. 2x

25
Q

What is the relationship b/t [Creatinine] and GFR?

A

[Creatinine] doubles each time GFR drops in half.

26
Q 
Interpreting [Creatinine]:
Day 1: serum creatinine = 1.0 mg/dl
Day 100: serum creatinine = 4.0 mg/dl
Which best expresses GFR at day 100 compared to day 1?
A. 150%
B. 125%
C. 50%
D. 33%
E. 25%
A

E. 25% b/c 1 to 2 is doubling, 2-4 is double again (twice halved)

27
Q

T/F- BUN is commonly used clinical estimate of renal fxn.

A

True- but less accurate than serum creatinine
b/c urea production varies
urea is actively and passively reabsorbed by the kidneys

28
Q

Define Azotemia.

A

Azotemia is inc. levels of nitrogenous wastes in blood (BUN and serum creatinine)

29
Q

What processes may be responsible for Azotemia?

A

Any that lowers GFR: reduced perfusion of the kidneys (pre-renal), Primary kidney disease (renal), or obstruction to the flow of urine (post-renal) –> pressure backfills see enlargement upstream of the obstruction

30
Q

What signs would suggest prerenal azotemia?

A

If kidney normal –> highly conc. urine (>1.030)

rapid correction of azotemia when corrected

31
Q

What signs would suggest renal azotemia?

A

Inability to conc. adequately

Cannot correct medically (ie. fluids or drugs)

32
Q

What signs would suggest post renal azotemia?

A

Unable to void or anuria (no urine), dilation of collecting system upstream.

33
Q

How is (Effective renal plasma flow) ERPF measured?

A

ERPF is measured by clearance of para-aminohippuric acid (PAH), it is completely extracted from plasma during passage through nephron. (largely removed by secretion)

34
Q

Define hematocrit.

A

Fraction of blood containing RBC

(1-Hct)=fraction of blood occupied by plasma

35
Q

What is “fractional excretion”?

A

ratio of clearance of “A” to GFR,

compare clearance of X to creatinine, how is kidney handling this substance? there are normal values for this.

36
Q

Meaning of clearance ratios:

a. if Cx/C(GFR) = 1.0 ?
b. if Cx/C (GFR) 1.0 ?

A

a. they are the same, the substance is only affected by glomerular filtration
b. less of it in the urine, may be reabsorbed/metabolized, or not freely filtered.
c. kidney is losing too much

37
Q

Why is PAH used to measure ERPH?

A

B/c it is nearly completely eliminated by filtration plus secretion in a single pass through the kidneys.

Renal Physiology (6 decks)

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