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SMP - Renal > PSW 2 - Assessment of Tubular Function > Flashcards

PSW 2 - Assessment of Tubular Function Flashcards

1
Q

What is a way to quantitate the renal contribution to the regulation of body fluid osmolarity? Equation?

A

Determine the amount of solute-free water that is excreted/reabsorbed by the kidney = amount of pure (or solute-free) water that would have to be added to or removed from the urine to make the urine isosmotic to plasma

V = Cosm + CH2O

V = urine flow rate
Cosm = solute clearance 
CH2O = free water clearance

Cosm = Urine osmolarity.V/Plasma osmolarity

=> CH2O = V - Uosm.V/Posm

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2
Q

If a HYPOsmotic urine is formed, then is free water clearance positive or negative?

A

Positive

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3
Q

If a HYPERosmotic urine is formed, then is free water clearance positive or negative? What does this mean? Symbol?

A

Negative => solute-free water is being reabsorbed, not excreted, in order to form urine more concentrated than plasma

Symbol = TcH2O = the volume of free water transported

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4
Q

If the clearance of a substance is above the GFR, what does this mean?

A

Means it is also secreted by the kidney

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5
Q

If the clearance of a substance is above the clearance of another, what does this mean?

A
  1. Secreted MORE by the kidney

2. Better filtered at the glomerulus

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6
Q

How to compare clearances quantitatively?

A

If Ca>Cb, then Cb/Ca x 100 = x% =>

  1. Cb is being excreted at x% of the rate at which Ca is being excreted
  2. Cb is being reabsorbed at 100-x% of the rate at which Ca is being reabsorbed
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7
Q

How to relate excretion fraction, FE, and GFR?

A

FE = Cx/GFR

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8
Q

How can you calculate FE only with urine and plasma concentrations of creatinine and the substance X? What is this called?

A

FE = Cx/GFR = (Ux/Px).V/(Ucr./Pcr).V = (Ux/Px)/(Ucr./Pcr)

Called the double ratio

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9
Q

How to calculate clearance when a substance does not readily filter at the glomerulus?

A

C = U.V / (FF.P)

FF = fraction filtered

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10
Q

What % Mg2+ is bound by plasma proteins?

A

50%

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11
Q

What is the free water clearance if the urine is isosmotic?

A

0

CH2O = V - [Uosm.V/Posm] = V-V=0

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12
Q

Why is the ability of the kidney to excrete solute free water important?

A

Because when we drink a lot, we are diluting plasma osmolarity so we need to be able to excrete it

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13
Q

Unit of CH2O, free water clearance?

A

mL/min

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14
Q

What factors influence the formation of either positive or negative CH2O?

A

Factors that allow for the formation of dilute or concentrated urine

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15
Q

What drug would cause the free water clearance to go from positive to negative?

A

ADH analog that only affects the V2 receptors on the kidney (not the vascular ones that cause vasoconstriction)

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16
Q

Does changing the dietary sodium intake change the sodium plasma concentration? Explain.

A

NOPE, would just cause ECF/ICF water shifts as sodium controls plasma osmolarity

Plasma sodium levels are not an indication of sodium, but an indication of plasma water volume

17
Q

How to calculate ERBF when you have ERPF?

A

ERBF = ERPF/(1-hematocrit)

18
Q

How can you calculate the total amount of water reabsorbed in a day?

A

GFR - V over 24 hours

19
Q

Average daily Na+ excreted?

A

150 mmol/day

20
Q

How to calculate the fractional excretion of water? What is important to note?

A

Equivalent to % GFR excreted

FE=V/GFRx100

Note: this is NOT solute free water

21
Q

How to relate FE of water to plasma and urine inulin/creatinine?

A

FE = Pin/Uin
OR
FE = Pcr/Ucr

22
Q

The higher Uin/Pin…

A

The more water was reabsorbed by the kidney

23
Q

How to calculate the GFR of a single nephron? What to note?

A

SNGFR = TFin.TFR/Pin = 100 mL/min/2M nephrons = average GFR of 50 nl/min => STAYS CONSTANT THROUGHOUT TUBULE because as TFin/Pin goes up, TFR goes down

TFin = tubular fluid inulin concentration
TFR = tubular flow rate
24
Q

What is the micropuncture technique? What is it used for?

A

Puncture a tubule, block it distally, and use a pipette to collect the incoming tubular fluid => used to measure tubular flow and concentrations throughout a nephron

25
Q

What would the TFin/Pin ratio be in Bowman’s space?

A

1

26
Q

What would the TFin/Pin ratio be mid-proximal tubule?

A

> 1

27
Q

What is fractional delivery of water? Include overall and in a single nephron.

A

Fractional excretion inside 1 tubule = fraction of GFR still present inside the tubule = V/GFR = V / Cin = 1/TFin/Pin = Pin/TFin

28
Q

What can we assume if the tubular fluid inulin to plasma inulin ratio is increasing?

A

Flow rate in tubule is proportionally decreasing

29
Q

How to calculate fractional reabsorption in a single nephron?

A

1 - Pin/TFin

30
Q

What is fractional delivery of a substance?

A

Fraction of substance still present in tubule at a particular point = (TFx/Px)/(TFin./Pin)

31
Q

Log(x) = 0… x=>

A

1

32
Q

At what site in the nephron is transepithelial potential difference of greatest magnitude?

A

End of DCT/beginning of CD

33
Q

When given a problem where a patient is urinating at different times, how to calculate V?

A

You are calculating urine production essentially, so pick at time at which she urinated at a starting point and use the volume peed at the next time and the time difference between the 2 (DO NOT ADD VOLUME)

34
Q

What is the % TBW of an adult?

A

60% of weight

35
Q

What is the % ECF of an adult?

A

1/3rd of TBW

36
Q

What is the % plasma of an adult?

A

1/4th of ECF

37
Q

What does the “insensible waterloss” mean?

A

The amount of fluid lost on a daily basis from the lungs and skin

38
Q

How to calculate minimum volume of urine based on osm intake and urine concentration?

A

osm intake/urine osm

SMP - Renal (20 decks)

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