Lecture 3: Measuring GFR & Renal Clearance Flashcards

1
Q

what is clearance

A

the volume of plasma from which all of the substance is removed and excreted in a given time

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2
Q

how to calculate clearance

A

Ux = urine concentration
V- = urine flow rate
Px = plasma concentration
Cx = clearance

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3
Q

why can inulin be used to determine GFR

A

b/c it is freely filtered and neither secreted nor reabsorbed by the tubules

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4
Q

example of a substance that is freely filtered and also secreted and absorbed

A

Sodium. secreted, but most (99%) gets reabsorbed

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5
Q

how can a solute have a greater clearance than GFR of 150ml/min

A

if the solute is secreted

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6
Q

what is creatinine

A

waste product formed in muscle from creatine phosphate

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7
Q

how much (%) creatinine is filtered at the glomerulus

A

15-20% of plasma creatine is filtered

the portion that is not filtered is returned to systemic circulation via the renal vein

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8
Q

What is the relationship b/w plasma creatinine concentration and GFR

A

they are inversely related

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9
Q

why isn’t creatinine a perfect substance for measuring GFR

A

b/c some of it gets secreted in the proximal tubules

*so creatinine clearance tends to be an over-estimation of GFR

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10
Q

what health conditions cause BUN to rise

A
  • heart failure (↓ RBF, ↓GFR)
  • dehydration (↓ RBF, ↓ GFR)
  • high protein diet (↑protein metabolism)
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11
Q

what health conditions cause BUN to decrease

A
  • liver disease (↓ protein catabolism)
  • malnutrition (↓ protein catabolism)
  • fluid overload (↑RBF, ↑GFR, ↑ urine flow)
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12
Q

What is BUN

A

blood urea nitrogen
- the amount of nitrogen derived from urea

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13
Q

what does the level of urea in blood (BUN) reflect

A

protein intake, protein metabolism, renal handling of urea

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14
Q

renal urea excretion must match ____ otherwise, plasma levels would become pathological (uremia)

A

hepatic production

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15
Q

the clearance of a substance the is freely filtered and not reabsorbed/secreted is a useful approach to determine _____ ?

A

GFR

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16
Q

when does creatinine clearance change

A

when GFR chagnes

16
Q

what is the effect of plasma creatine concentration and urine flow on creatinine clearance ?

A

neither the plasma creatinine concentration nor the urine flow has an effect on creatinine clearance b/c creatinine clearance depends on GFR and these factors do not affect GFR

17
Q

equation for calculating creatinine clearance

A
17
Q

plasma creatinine concentration is an indicator of ?

A

GFR