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Renal - Physiology > Fluids, Filtration > Flashcards

Fluids, Filtration Flashcards

1
Q

What % of body mass is total body water?

A

60%

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2
Q

What fraction of total body water is extracellular? Ie, what % of total body mass is extracellular fluid?

A

1/3

1/3 * 60% = 20% of total body mass.

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3
Q

What fraction of total body water is intracellular? Ie, what % of total body mass is intracellular fluid?

A

2/3

2/3 * 60% = 40% of total body mass.

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4
Q

What can radiolabeled albumin measure?

A

plasma volume

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5
Q

What can inulin measure?

A

extracellular volume

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6
Q

What is normal osmolality?

A

285-295 mOsm.

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7
Q

Of extracellular fluid, what % is interstitial fluid, and what % is plasma volume?

A

75% interstitial, 25% plasma.

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8
Q

What does the glomerular filtration barrier filter plasma according to?

A

Size and net charge.

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9
Q

What are the three components of the glomerular filtration barrier?

A

Fenestrated capillary endothelium
Fused basement membrane with heparan sulfate
Epithelial layer consisting of podocyte foot processes.

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10
Q

Which component of the glomerular filtration barrier is the size barrier?

A

Fenestrated capillary endothelium

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11
Q

Which component of the glomerular filtration barrier is the charge barrier?

A

Fused basement membrane w/ heparan sulfate

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12
Q

Which barrier is lost in nephrotic syndrome?

A

Charge barrier. Leads to albuminuria, hypoproteinemia, hyperlipidemia, edema etc.

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13
Q

What do podocytes wrap around?

A

Glomerular capillaries.

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14
Q

Why can inulin be used to calculate GFR?

A

It is freely filtered and neither reabsorbed nor secreted.

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15
Q

What is used clinically to calculate GFR?

A

Creatinine

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16
Q

Why is creatinine an imperfect measure of GFR?

A

Creatinine is mildly secreted by renal tubules

17
Q

Does creatinine overestimate or underestimate GFR?

A

Overestimates, because the renal tubules are secreted - adding to the “cleared” number.

18
Q

What can be given to make creatinine a more accurate measure?

A

Cimetidine. It decreases tubular secretion of Cr.

19
Q

What does (Ux * V)/Px describe?

A

Clearance; volume of plasma from which the substance is completely clear per unit time.

20
Q

If Cx > GFR, what does that mean?

A

Net tubular secretion of X.

21
Q

If Cx < GFR, what does that mean?

A

Net tubular reabsorption of X.

22
Q

What is used to measure effective renal plasma flow?

A

para-aminohippuric acid (PAH). PAH is both filtered AND secreted in the PCT, resulting in near 100% excretion.

23
Q

What is the difference between GFR and effective renal plasma flow, conceptually?

A

Inulin measures what gets through the filtration barrier and assumes no action beyond that; this measures GFR.
PAH measures what gets through the filtration barrier and what is excreted from the blood - it is a more accurate measure of excretion.

24
Q

What is the equation for effective renal plasma flow?

A

Same as clearance, using PAH:

(Upah * V)/Ppah

25
Q

How does effective renal plasma flow relate to renal blood flow?

A

RBF= RPF /(1-Hct)

26
Q

How the heck does the eRPF to RBF formula make sense?

A

Rearrange!
RBF * (1-Hct) = RPF
RBF - RBF(Hct) = RPF
Renal blood flow - (% that is RBCs) = Renal plasma flow

27
Q

Is calculated eRPF accurate?

A

It underestimates by 10% - eRPF is actually 90% of RPF.

28
Q

What is filtration fraction?

A

GFR/RPF

29
Q

What is filtration fraction conceptually?

A

Of the amount that is flows through kidney, what percent came through the glomerulus.

30
Q

What actions do NSAIDs have on renal arterioles?

A

Blocks dilation of the afferent arteriole.

31
Q

What effect does afferent arteriole constriction have on GFR, RPF, and FF? (NSAIDs)

A

GFR and RPF decrease, FF is constant.

NSAIDs

32
Q

What actions do ACEis have on renal arterioles?

A

Blocks constriction of the efferent arteriole.

33
Q

What effect does efferent arteriole constriction have on GFR, RPF, and FF?

A

Increases the GFR, and decreases the RPF. FF increases.

ACEIs decrease GFR, increase RPF, FF decreases.

34
Q

What effect does an increase in plasma protein have on GFR, RPF, and FF?

A

Decreases GFR and FF (increased oncotic pressure keeping things in the capillaries). No change on RPF.

35
Q

What effect does a decrease in plasma protein have on GFR, RPF, and FF?

A

Increases GFR and FF. No change in RPF.

36
Q

What does GFR + Px represent?

A

Filtered load

37
Q

What does Ux * V represent?

A

Excretion rate

38
Q

What does Filtered-excreted =

A

Reabsorption

39
Q

What does Excreted - filtered =

A

Secretion.

Renal - Physiology (6 decks)

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