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Physiology > Renal Clearance > Flashcards

Renal Clearance Flashcards

1
Q

What are the units of clearance?

A

Volume per unit time

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2
Q

What are the 3 processes in the nephron?

A

Glomerular Filtration
Resorption of the Substance into Blood
Secretion of the Substance into Tubule

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3
Q

What are the renal units for concentration?

A

mg/mL

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4
Q

What are the renal units for flow?

A

mL/min

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5
Q

What are the renal units for load?

A

mg/min

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6
Q

Pax

A

Concentration x in Arterial Plasma

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7
Q

Pvx

A

Concentration x in Venous Plasma

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8
Q

Ux

A

Concentration x in Urine

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9
Q

RBF

A

Renal Blood Flow

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10
Q

RPF

A

Renal Plasma Flow

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11
Q

GFR

A

Glomerular Filtration Rate

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12
Q

V

A

Urine Flow Rate

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13
Q

What is the kidney input load equal to?

A

Pax + RPFa

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14
Q

What is the kidney output load equal to?

A

(Pvx * RPFv) + (Ux * V)

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15
Q

If urine flow rate V>0mL/min then how are the values of the RFPa and RFPv affected?

A

RPFa > RPFv

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16
Q

What is the equation for conservation of mass in regards to renal function?

A

Pax + RPFa = (Pvx * RPFv) + (Ux * V)

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17
Q

What are the loads that enter the tubule?

A

F - filtered load

S - secreted load

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18
Q

What are the loads that leave the tubule?

A

R - reabsorbed load

E - excreted load

19
Q

What is the filtered load equal to?

A

Pax * GFR

20
Q

What is the excreted load equal to?

A

Ux * V

21
Q

What is clearance?

A

It is defined as the volume of plasma completely cleared of any substance in one minute

22
Q

What is the range of clearance?

A

0 to RPF (maximum)

23
Q

What is the RPF in terms of the cardiac output?

A

RPF is around 25% of the cardiac output

24
Q

How much of the RPF does the kidney filter?

A

20% -> this is the GFR

25
Q

What is the formula for clearance?

A

Cx = Ux * (V/Px)

Px - plasma concentration of x

26
Q

Why is the venous return ignored in clearance?

A

Venous blood is returned to the body

27
Q

What happens if Cx < GFR?

A

Substance x is filtered and reabsorbed

28
Q

What happens if Cx = GFR?

A

x is only filtered

29
Q

What happens if Cx > GFR?

A

x is filtered and secreted

30
Q

What is the clearance range for glucose and proteins?

A

Cx = 0 usually

31
Q

What is the clearance range for inulin and creatinine?

A

Cx = GFR

32
Q

What is the clearance range for PAH and organic dyes?

A

Cx = RPF

33
Q

What substances can give an accurate measurement of GFR?

A

Substances that are filtered by the glomerulus but neither secreted nor reabsorbed would be an accurate measurement of the GFR.

F = E in this case as S and R = 0

34
Q

What are the advantages of using inulin to determine GFR?

A
  • It is neither reabsorbed or secreted so S and R = 0
  • Neither produced or consumed by kidneys
  • Easily measurable
  • Nontoxic
35
Q

What are the disadvantages to using inulin to determine GFR?

A
  • It must be infused constantly

- It is expensive

36
Q

What are the advantages to using creatinine to determine GFR?

A
  • It is a natural metabolic product of skeletal muscle metabolism
  • Not reabsorbed so R=0
  • Neither produced or consumed by kidneys
  • Nontoxic
  • Easily measured
  • Constantly being infused naturally
  • “Free” so it is cheap
37
Q

What are the disadvantages of using creatinine to determine GFR?

A

-10% is secreted so S>0

38
Q

Which method of measuring GFR is more accurate?

A

Inulin

39
Q

Which method of measuring GFR is more accessible?

A

Creatinine

40
Q

How does the value of the GFR measured by the creatinine method differ from the true value?

A

It is overestimated by around 10%

41
Q

What is BUN and how is it used?

A

It is the blood urea nitrogen and it is used to roughly estimate GFR.

42
Q

What is the relationship between GFR and PCr?

A

As the GFR decreases, the PCr will increase as the excretion is falling while the production rate remains constant.

43
Q

Why is PAH a good estimation for RPF?

A

It is not normally found in the body and it is freely filtered and secreted by the proximal tubule and more is removed than what is filtered.

R=0 as none is reabsorbed.

44
Q

What is the RPF equal to?

A

RPF = RBF * (1-Hematocrit)

Physiology (81 decks)

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