RBF, GFR, and Clearance Flashcards

1
Q

Normal RBF

A

1.3 Liter/min

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2
Q

Normal Renal Plasma Flow (RPF)

A

0.65 Liter/min

Assuming RBF of 1.3 Liter/min and HCT = 50%

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3
Q

Normal GFR

A

130 ml/min

20% of RPF

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4
Q

What is the molecular size cut-off of the glomerular filtration apparatus?

A

~60,000 daltons

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5
Q

Starling Equation

A

GFR = K (Pg - Pt - PIgc)

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6
Q

Prostaglandins - 2 functions

A

Produced by medullary interstitial cells in response to Angiotensin II

Dilate afferent arteriole of the glomerulus, maintaining adequate RBF; blunts the effect of AgII on renal arteriole constriction, protecting against acute renal failure in hypovolemia

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7
Q

Glomerulotubular Balance

A

The ability of the obligatory reabsorption mechanisms in the proximal tubule to compensate for changes in the filtered load such that a fixed proportion of the the filtered load of water and NaCl is always reabsorbed (65%)

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8
Q

Tubuloglomerular Feedback

A

Increased GFR causes a rise in tubular fluid flow, which decreases the proportional reabsorption of NaCl; increased NaCl concentration is sensed by the Macula Densa at the beginning of the DCT, which paracrine signals the afferent arteriole to contract,, thus returning GFR to normal

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9
Q

Macula densa

A

A group of specialized, NaCl sensitive cells at the start of the distal tubule; they monitor the status of obligatory reabsorption just before the filtrate enters the fine tuning segments and can cause the afferent arteriole to dilate or constrict

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10
Q

Clearance - Definition & Equation

A

The volume of plasma from which all of substance X is removed per unit time

Clearance = U[X] x V / P[X]

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11
Q

Effects of NSAIDS on GFR

A

NSAIDS shut down the prostaglandin-mediated vasodilation of the afferent arteriole, causing vasoconstriction and potential renal failure

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12
Q

Effects of ACEIs/ARBs on GFR

A

ACEIs/ARBs shut down the Angiotensin II mediated vasoconstriction of the efferent arteriole in response to decreased MAP, causing reduced GFR

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13
Q

24 hour urine collection

A

Uses the formula ClCr = UCr x V / PCr

Clearance is calculated from the urine creatinine, plasma creatinine, and urine flow rate (volume of urine collected / 1,440 minutes)

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14
Q

BUN

A

Urea is a nitrogenous waste that is endogenously produced from protein; it is reabsorbed at several tubular sites and therefore underestimates GFR

Plasma concentration of BUN depends both on renal clearance and rate of protein catabolism (muscle mass)

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15
Q

Creatinine

A

Creatinine is a breakdown product of creatine kinase found in muscles; it is secreted to varying degrees by the renal tubule and therefore tends to overestimate GFR by 10-20%

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16
Q

Cockcroft and Gault formula

A

Creatinine clearance = [(A) x (140-age) x weight] / (72 x SCr)

Where A = 1.0 of male or 0.85 if female

17
Q

Normal Serum Creatinine

A

1.0 +/- 0.3 mg/dL

18
Q

Normal BUN

A

12 +/- 4 mg/dL