Renal Function Tests- Rao

Question 1

What is mass flow?

Answer 1

the expression of solute movements as a function of time (amt/min)

Question 2

The equation for mass flow in a solution? What do you need to know to be able to solve for Mass flow?

Answer 2

a) Mass Flow= Concentration x Volume Flow (Rate of flow??)= (amount/ml) x (ml/min)
b) concentration and rate of flow for a given solute

Question 3

Explain what is meant by Homeostasis (or mass balance for the whole body)?

Answer 3

The body normally maintains a constant total content of all substances, including water, solutes, and solid material stores.

Question 4

What 3 factors influence total body content?

Answer 4

Intake (food, drink), Production (from metabolism), output (urine, feces, respiration)

Question 5

Equation for maintaining mass balance?

Answer 5

Rate of Output=Rate of Intake+Rate of Production

Question 6

What is the extra factor involved in some ingested solutes such as glucose that can be metabolized? Equation?

Answer 6

It can be metabolized, so C, H, and O balance is maintained, rather than just glucose balance.
Rate of Output (as CO2 and H2O)=Rate of Intake+(Rate of Production-Metabolism)

Question 7

For solutes produced only by metabolism, what is the equation of mass balance? Examples?

Answer 7

Urea, Uric acid
Rate of Output=Rate of Production
There is NO intake of these solutes because they are not ingested

Question 8

Mass balance of a solute that is not produced by the body, only ingested?

Answer 8

NaCl

Rate of Output=Rate of Intake

Question 9

At steady state, the plasma concentration of solute X will be__________?

Answer 9

Constant

Question 10

What is the equation of mass balance in the Kidney? How does output leave the kidney? Input?

Answer 10

Rate of input to Kidney= Rate of output from kidney;
Output via Renal Vein, Lymphatics, or Urine
Input: In Renal Artery

Question 11

What does the Mass Flow in the kidney equal?

Answer 11

MF in Kidney=Rate of flow in 4 different routes times Concentration in each route

Question 12

Equation of Mass Balance of water and solutes along the nephron?

Answer 12

Rate of Input=Output: So,
Filtration+Secretion=Reabsorption+Excretion
F+S=R+E

Question 13

a) Rate of Filtration or Excretion=?
b) Filtration rate = what for a given solute?
c) Excretion rate= what for a given solute?

Answer 13

a) Rate of F/E= Solute conc x Volume Flow Rate
b) F Rate= GFR x Plasma Conc
c) E Rate= UF(urine flow) x Urinary Conc

Question 14

What is the use of quantitative renal function analysis?

Answer 14

It is an indicator of the extent and progression of renal diseases.

Question 15

Measurement of what three important parameters enable quantification of kidney function?

Answer 15

1. GFR 2. Plasma Clearance of Solutes 3. Renal Blood Flow

Question 16

Loss of glomeruli due to sclerosis/destruction would have what kind of effect on GFR?

Answer 16

It would proportionally decrease GFR

Question 17

What is a way to measure kidney function?

Answer 17

Infuse a substance and analyze its excretion in urine and the maintenance of its plasma concentration.

Question 18

What characteristics of inulin (fructose polymer) make it an ideal substance for the analysis of kidney function?

Answer 18

It is not produced or metabolized in the body. It is only excreted in the urine by the kidney.

Question 19

For a given solute, what how is its plasma concentration P[X] determined?

Answer 19

P[X]= Rate of Infusion(mg/min)/Rate of Output(mL/min)
Rate of infusion=Input+Production
Rate of Output=Metabolism+Excretion

Question 20

Why is Inulin the model for measuring GFR?

Answer 20

It is not produced or metabolized in the body; it excreted only by the kidney in the urine; it is not reabsorbed or secreted by the tubule.

Question 21

Because Rate of Filtration=Rate of Excretion for inulin, what is inulin clearance equal to?

Answer 21

Inulin Clearance= (U[in] x V) / P[in] = GFR;

Inulin Clearance=GFR

Question 22

Definition of Clearance:

Answer 22

The volume of plasma that is completely cleared of the substance by the kidney per unit time

Question 23

How do you solve for clearance of Substance X

Answer 23

C=(U[X] x V) / P[X]

Question 24

How does Clearance of a solute compare to C of inulin and GFR, if it reabsorbed?

Answer 24

If a substance is reabsorbed, its clearance is less than GFR or Cin.

Question 25

What is a substance is secreted?

Answer 25

If a substance is secreted, its clearance > GFR for that substance

Question 26

What is an extraction ratio? what is the equation for Extr Ratio of x?

Answer 26

Percentage of substance removed from plasma;

Ex Ratio x = (A[x]-V[x]) / A[x]

Question 27

How is the Ex ratio affected by reabsorption? By secretion?

Answer 27

Reabsorption results in a low extraction ratio; Secretion increases the extraction ratio.

Question 28

If substance x is completely cleared from the plasma, Clearance of x= what?

Answer 28

Clearance x = total RPF

Question 29

How is PAH handled by the kidney? What is its extraction ratio?

Answer 29

It is secreted by the tubule; Its extraction ratio is ~1 (0.9-0.95) or 90-95% clearance

Question 30

What parameter is clearance of PAH used to estimate?

Answer 30

C(PAH)= Effective RPF (eRPF)

C(PAH) / (Ex Ratio PAH)= eRPF

Question 31

How do you solve for RBF?

Answer 31

RPF/(1-Hct)

Question 32

What is the commonly used endogenous indicator of GFR?

Answer 32

Creatinine

Question 33

What characteristics of Cr make it useful as indicator of GFR?

Answer 33

It’s plasma concentration is constant in normal patient; it’s freely filtered, not reabsorbed, and only slightly secreted

Question 34

How does Cl(Cr) compare to that of inulin and GFR.

Answer 34

It is slightly higher than Cl(in) and GFR, but still used as a rough estimate of GFR.

Question 35

What is the relationship between plasma Cr and GFR?

Answer 35

They are inversely related; as GFR decreases, plasma creatinine increases.

Question 36

What happens to the rate of creatinine excretion immediately after nephrectomy (GFR decreases to half)?

Answer 36

Urinary output of Cr likely drops to half, look at slide for other changes