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Renal > GFR, RPF, RBF, Clearance > Flashcards

GFR, RPF, RBF, Clearance Flashcards

1
Q

Filtered, but neither reabsorbed nor secreted by renal tubules

A

inulin

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2
Q

GFR formula = C (inulin) =

A

[(urine concentration of inulin)(urine flow rate)] / (plasma concentration of inulin)

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3
Q

Effect of age on GFR?

A

decrease

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4
Q

effect of decreased GFR on BUN?

A

increase

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5
Q

effect of decreased GRF on plasma[creatinine]

A

increase

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6
Q

effect of decreased GFR on extracellular potassium?

A

increase

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7
Q

what three things does decreased GFR result in?

A

Increased BUN, creatinine, extracellular potassium

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8
Q

In prerenal azotemia (hypovolemia), BUN increases more than serum creatinine →

A

increased BUN/creatinine ratio (> 20:1)

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9
Q

GFR = Kf [ (HPgc – HPbs) – (OPgc – OPbs)]

A

Starling equation

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10
Q

Filtered Load (amount of substance Z filtered per unit time) =

A

GFR * [plasma concentration Z]

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11
Q

Excretion Rate =

A

V * Ux

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12
Q

Excretion rate also =

A

(filtered load) – (reabsorption rate) + (secretion rate)

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13
Q

When glomerular capillary oncotic pressure decreases, what happens to GFR?

A

Increase

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14
Q

A BUN/creatinine ratio > 20:1 is indicative of what condition?

A

Prerenal azotemia (hypovolemia)

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15
Q

What is the driving force for glomerular filtration?

A

net ultrafiltration pressure across the glomerular capillaries

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16
Q

Bowman’s space oncotic pressure

A

Is usually zero since only a small amount of protein is filtered

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17
Q

Means of increasing HPgc (glomerular capillary hydrostatic pressure)

A

Dilation of afferent arteriole or constriction of efferent arteriole will increase HPgc

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18
Q

Constriction of ureters will increase HPbs

A

HPbs – Bowman’s space hydrostatic pressure

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19
Q

Decrease in oncotic pressure in glomerular capillary –>

A

Increased GFR

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20
Q

OPgc decreases by decreases in capillary protein concentration

A

cirrhosis or nephrotic syndrome

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21
Q

Relative clearances

A

PAH > K > inulin > urea > Na > glucose, amino acids, and HCO3-

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22
Q

The ability to dilate urine

A

Free water clearance

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23
Q

Free Water Clearance (CH2O) =

A

V – Cosm
where V = urine flow rate (ml/min) and
Cosm = osmolar clearance (UosmV/Posm)

24
Q

With ADH: CH2O < 0

A

(retention of free water)

25
Q

Without ADH: CH2O > 0

A

(excretion of free water)

26
Q

Isotonic urine: CH2O = 0

A

(seen with loop diuretics)

27
Q

the volume of plasma cleared of a substance per unit time

A

Clearance

28
Q

equation for clearance

A

C (x) = U (x) V / P (x)

29
Q

RBF is directly proportional to

A

pressure difference between the renal artery and the renal vein

30
Q

RBF is inversely proportional to

A

the resistance of the renal vasculature

31
Q

Autoregulation of RBF is achieved by changing

A

renal vascular resistance; RBF remains constant over a range of arterial pressures

32
Q

Myogenic mechanisms of RBF autoregulation:

A

afferent arterioles contract in response to stretch caused by increased arterial pressure

33
Q

Tubuloglomerular feedback:

A

increased renal arterial pressure leads to ↑ delivery of fluid to the macula densa. The macula densa secretes paracrine signals that lead to constriction of the nearby afferent arteriole.

34
Q

RBF is related to RPF (Renal Plasma Flow) by the expression:

A

RBF = [ RPF / (1-Hematocrit) ]

35
Q

Renal plasma flow can be approximated by measuring the clearance of

A

PAH (paraaminohippuric acid)

36
Q

Why is PAH clearance a good representation of effective renal plasma flow (RPF)?

A

PAH is both filtered and secreted by the renal tubules (ie, none is reabsorbed)

37
Q

Why does PAH clearance underestimate the true RPF by about 10%?

A

it doesn’t measure RPF to regions of the kidney not involved in the filtration and secretion of PAH

38
Q

Effective RPF:

A

C (PAH) = [Urine] PAH x V / [Plasma] PAH

39
Q

Filtered load of glucose is directly proportional to

A

plasma [glucose]

40
Q

What reabsorbs glucose?

A

Na-glucose cotransport in the proximal convoluted tubule (there are a limited number of these Na-glucose carriers)

41
Q

lowest plasma [glucose] at which glucosuria occurs.

A

Threshold =

Threshold ~180mg/dL.

42
Q

glucose reabsorption rate at which all Na-glucose carriers are saturated ∴

A

Transport maximum

43
Q

Tm is directly proportional to the number of.

A

functioning glucose transporters

functioning nephrons.

44
Q

Tm in adult males

A

~375mg/min, which corresponds to a plasma [glucose] of 300mg/dL if GFR is 1.25dL/min [ 300mg/dL x 1.25dL/min = 375mg/min ]

45
Q

If plasma [glucose] < 180mg/dL →

A

plenty of Na-glucose carriers are available:
- all filtered glucose is reabsorbed
∴ excretion of glucose is zero.

46
Q

If plasma [glucose] > 300mg/dL →

A

all Na-glucose carriers are saturated:

- reabsorption is saturated ∴ any additional ↑ in plasma [glucose] results in glucosuria

47
Q

If plasma [glucose] is between 180mg/dL and 300mg/dL,

A

some Na-glucose carriers are saturated while others are not, and the degree of Na-glucose carrier saturation varies from nephron to nephron (splay)

48
Q

“Splay” represents glucosuria before reabsorption is fully saturated, and can be explained by:

A

1) Nephron heterogeneity

2) Relatively low affinity of Na-glucose cotransporters

49
Q

equation for filtration fraction

A

FF = GFR / RPF

50
Q

the fraction of RPF (renal plasma flow) filtered across the glomerular capillaries. The amount filtered becomes the urine.

A

FF (filtration fraction)

51
Q

Normal FF

A

20%

80% leaves through efferent arterioles to enter the peritubular capillaries

52
Q

↑ in FF leads to

A

↑ protein concentration of peritubular capillary blood, which leads to increased reabsorption in the proximal tubule

53
Q

↓ in FF leads to

A

↓ in the protein concentration of peritubular capillary blood and decreased reabsorption in the proximal tubule

54
Q

↑ HPgc –>

A

↑ GFR
if pressure is increased inside the glomerular capillary, then there will be a greater driving force pushing plasma through the capillary wall.

55
Q

↑ HPbs –>

A

↓ GFR

56
Q

↑OPgc –>

A

↓ GFR

57
Q

↓ HPgc –>

A

↓ GFR

Renal (22 decks)

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