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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
Without ADH: CH2O > 0
(excretion of free water)
26
Isotonic urine: CH2O = 0
(seen with loop diuretics)
27
the volume of plasma cleared of a substance per unit time
Clearance
28
equation for clearance
C (x) = U (x) V / P (x)
29
RBF is directly proportional to
pressure difference between the renal artery and the renal vein
30
RBF is inversely proportional to
the resistance of the renal vasculature
31
Autoregulation of RBF is achieved by changing
renal vascular resistance; RBF remains constant over a range of arterial pressures
32
Myogenic mechanisms of RBF autoregulation:
afferent arterioles contract in response to stretch caused by increased arterial pressure
33
Tubuloglomerular feedback:
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
RBF is related to RPF (Renal Plasma Flow) by the expression:
RBF = [ RPF / (1-Hematocrit) ]
35
Renal plasma flow can be approximated by measuring the clearance of
PAH (paraaminohippuric acid)
36
Why is PAH clearance a good representation of effective renal plasma flow (RPF)?
PAH is both filtered and secreted by the renal tubules (ie, none is reabsorbed)
37
Why does PAH clearance underestimate the true RPF by about 10%?
it doesn’t measure RPF to regions of the kidney not involved in the filtration and secretion of PAH
38
Effective RPF:
C (PAH) = [Urine] PAH x V / [Plasma] PAH
39
Filtered load of glucose is directly proportional to
plasma [glucose]
40
What reabsorbs glucose?
Na-glucose cotransport in the proximal convoluted tubule (there are a limited number of these Na-glucose carriers)
41
lowest plasma [glucose] at which glucosuria occurs.
Threshold = | Threshold ~180mg/dL.
42
glucose reabsorption rate at which all Na-glucose carriers are saturated ∴
Transport maximum
43
Tm is directly proportional to the number of.
functioning glucose transporters | functioning nephrons.
44
Tm in adult males
~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
If plasma [glucose] < 180mg/dL →
plenty of Na-glucose carriers are available: - all filtered glucose is reabsorbed ∴ excretion of glucose is zero.
46
If plasma [glucose] > 300mg/dL →
all Na-glucose carriers are saturated: | - reabsorption is saturated ∴ any additional ↑ in plasma [glucose] results in glucosuria
47
If plasma [glucose] is between 180mg/dL and 300mg/dL,
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
“Splay” represents glucosuria before reabsorption is fully saturated, and can be explained by:
1) Nephron heterogeneity | 2) Relatively low affinity of Na-glucose cotransporters
49
equation for filtration fraction
FF = GFR / RPF
50
the fraction of RPF (renal plasma flow) filtered across the glomerular capillaries. The amount filtered becomes the urine.
FF (filtration fraction)
51
Normal FF
20% | 80% leaves through efferent arterioles to enter the peritubular capillaries
52
↑ in FF leads to
↑ protein concentration of peritubular capillary blood, which leads to increased reabsorption in the proximal tubule
53
↓ in FF leads to
↓ in the protein concentration of peritubular capillary blood and decreased reabsorption in the proximal tubule
54
↑ HPgc -->
↑ GFR if pressure is increased inside the glomerular capillary, then there will be a greater driving force pushing plasma through the capillary wall.
55
↑ HPbs -->
↓ GFR
56
↑OPgc -->
↓ GFR
57
↓ HPgc -->
↓ GFR

Renal (22 decks)

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