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Urinary Tract Physiology > Clearance > Flashcards

Clearance Flashcards

1
Q

Definition of clearance

A

the volume of blood or plasma that can be freed of a specified constituent in a specified time (usually one minute)

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2
Q

Name some clinical situations in which clearance measures may be necessary to estimate GFR

A
  • extremes of age and body size
  • severe malnutrition or obesity
  • disease of skeletal muscle
  • paraplegia
  • vegetarian diet
  • rapidly changing kidney function
  • prior to dosing drugs with significant toxicity
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3
Q

Definition of renal clearance

A

the ability of the kidneys to remove a substances from the blood and excrete it into the final urine

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4
Q

Equation for renal clearance

A

Cx = (Ux/Px) x V

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5
Q

What is inulin used for?

A

used to measure clearance and GFR (b/c inulin is freely filtered, i.e. not reabsorbed, secreted, or metabolized by kidneys)

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6
Q

How do the clearances of insulin and inulin compare?

A. C (ins) > C (in)

B. C (ins) = C (in)

C. C (ins) < C (in)

A

C. C (ins) < C (in)

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7
Q

What are the units of clearance?

A

volume/time

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8
Q

How can filtrate produced be calculated?

A

by converting final urine into the volume of filtrate it is generated from

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9
Q

What is the number of mL of plasma filtered by the glomerulus in 1 minute?

Plasma concentration of creatinine is 1mg/dL

Urine produced in 1 minute is 20mL (0.2dL)

Urine creatinine concentration is 50mg/dL

A

Cx = (Ux/Px) x V

Cx = (50mg/dL / 1mg/dL) x (0.2dL/min)

Cx = 10dL/min

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10
Q

What is filtered load?

A

the amount of substance filtered into Bowman’s space per unit time (an amount, not a volume)

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11
Q
A

A (glomerulus)

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12
Q

Filtered load is measured as:

A. weight

B. weight per unit time

C. volume

D. volume per unit time

E. weight per unit volume

A

B. weight per unit time

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13
Q

When can GFR be measured as clearance for a substance X?

A

only when all of X delivered as filtrate is excreted in urine

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14
Q

Can creatinine be used instead of inulin?

A

yes, but some of it is secreted in male dogs

(no secretion with inulin)

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15
Q

What happens to serum creatinine concentration when GFR drops in half?

A

serum creatinine doubles

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16
Q

Day 1: Dog has a serum creatinine concentration of 1.0 mg/dL

Day 100: Dog has a serum creatinine concentration of 4.0 mg/dL

Which best expresses GFR at day 100 compared to day 1?

A. 150%

B. 125%

C. 50%

D. 33%

E. 25%

A

E. 25%

17
Q

Why are Urea and BUN less accurate than using serum creatinine to measure GFR?

A
  • urea production varies
  • urea is actively and passively reabsorbed by the kidneys
18
Q

What is azotemia?

A

increased levels of nitrogenous wastes in blood

19
Q

What can cauze azotemia?

A
  • reduced perfusion of the kidneys (prerenal)
  • primary kidney disease (renal)
  • obstruction to the flow of urine (postrenal)
20
Q

How can you tell the difference betwen prerenal, renal, and postrenal azotemia?

A
  • prerenal: concentrated urine (>1.030)
  • renal: inability to concentrate adequately
  • postrenal: unable to void or anuria (no urine)
21
Q

12 year old cat, PU/PD for 3 months

  • serum creatinine = 4.4mg/dL
  • urine specific gravity = 1.010

A. Prerenal

B. Renal

C. Postrenal

A

B. Renal

22
Q

3 year old cat unable to void, big bladder

  • serum creatinine = 4.4mg/dL
  • urine specific gravity = 1.028

A. Prerenal

B. Renal

C. Postrenal

A

C. Postrenal

23
Q

1 year old cat, 3 day vomiting and diarrhea

  • serum creatinine = 4.4mg/dL
  • urine specific gravity = 1.064

A. Prerenal

B. Renal

C. Postrenal

A

A. prerenal

24
Q

What are the characteristics of a marker (X) that would allow RPF measurement?

A
  • clearance of X must equal RPF
  • completely (or nearly so) extracted from plasma by filtration plus secretion
  • neither metabolized nor degraded by the kidneys
  • no organ other than the kidneys extracts X
  • cannot alter RPF
25
Q

How is effected renal plasma flow (ERPF) measured

A

measured as clearance of para-aminohippuric acid (PAH)

(PAH completely extracted from plasma during passage through nephron)

26
Q

What is hematocrit?

A

the fraciton of blood containing red blood cells

27
Q

What is the fraction of blood occupied by plasma?

A

1 - hematocrit

(1- Hct)

28
Q

Equation for ERBF

A

ERBF = ERPF / (1 - Hct)

29
Q

What do the following clearance ratios mean?

Cx / CGFR = 1.0

Cx / CGFR < 1.0

Cx / CGFR > 1.0

A

Cx / CGFR = 1.0 means substance X is cleared only by glomerular filtration

Cx / CGFR < 1.0 means substance X has limited filtration and/or reabsorption

Cx / CGFR > 1.0 means substance X is secreted

30
Q

Calculate clearance:

Plasma concentration: 4mg/dL

Urine concentration: 2.7mg/dL

Urine flow rate: 3mL/min

A. ~0.2 mL/min

B. ~0.45 mL/min

C. ~2.0 mL/min

D. ~4.5 mL/min

A

C. ~2.0 mL/min

Urinary Tract Physiology (9 decks)

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