Renal Function Tests- Rao Flashcards
What is mass flow?
the expression of solute movements as a function of time (amt/min)
The equation for mass flow in a solution? What do you need to know to be able to solve for Mass flow?
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
Explain what is meant by Homeostasis (or mass balance for the whole body)?
The body normally maintains a constant total content of all substances, including water, solutes, and solid material stores.
What 3 factors influence total body content?
Intake (food, drink), Production (from metabolism), output (urine, feces, respiration)
Equation for maintaining mass balance?
Rate of Output=Rate of Intake+Rate of Production
What is the extra factor involved in some ingested solutes such as glucose that can be metabolized? Equation?
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)
For solutes produced only by metabolism, what is the equation of mass balance? Examples?
Urea, Uric acid
Rate of Output=Rate of Production
There is NO intake of these solutes because they are not ingested
Mass balance of a solute that is not produced by the body, only ingested?
NaCl
Rate of Output=Rate of Intake
At steady state, the plasma concentration of solute X will be__________?
Constant
What is the equation of mass balance in the Kidney? How does output leave the kidney? Input?
Rate of input to Kidney= Rate of output from kidney;
Output via Renal Vein, Lymphatics, or Urine
Input: In Renal Artery
What does the Mass Flow in the kidney equal?
MF in Kidney=Rate of flow in 4 different routes times Concentration in each route
Equation of Mass Balance of water and solutes along the nephron?
Rate of Input=Output: So,
Filtration+Secretion=Reabsorption+Excretion
F+S=R+E
a) Rate of Filtration or Excretion=?
b) Filtration rate = what for a given solute?
c) Excretion rate= what for a given solute?
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
What is the use of quantitative renal function analysis?
It is an indicator of the extent and progression of renal diseases.
Measurement of what three important parameters enable quantification of kidney function?
- GFR 2. Plasma Clearance of Solutes 3. Renal Blood Flow
Loss of glomeruli due to sclerosis/destruction would have what kind of effect on GFR?
It would proportionally decrease GFR
What is a way to measure kidney function?
Infuse a substance and analyze its excretion in urine and the maintenance of its plasma concentration.
What characteristics of inulin (fructose polymer) make it an ideal substance for the analysis of kidney function?
It is not produced or metabolized in the body. It is only excreted in the urine by the kidney.
For a given solute, what how is its plasma concentration P[X] determined?
P[X]= Rate of Infusion(mg/min)/Rate of Output(mL/min)
Rate of infusion=Input+Production
Rate of Output=Metabolism+Excretion
Why is Inulin the model for measuring GFR?
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.
Because Rate of Filtration=Rate of Excretion for inulin, what is inulin clearance equal to?
Inulin Clearance= (U[in] x V) / P[in] = GFR;
Inulin Clearance=GFR
Definition of Clearance:
The volume of plasma that is completely cleared of the substance by the kidney per unit time
How do you solve for clearance of Substance X
C=(U[X] x V) / P[X]
How does Clearance of a solute compare to C of inulin and GFR, if it reabsorbed?
If a substance is reabsorbed, its clearance is less than GFR or Cin.
What is a substance is secreted?
If a substance is secreted, its clearance > GFR for that substance
What is an extraction ratio? what is the equation for Extr Ratio of x?
Percentage of substance removed from plasma;
Ex Ratio x = (A[x]-V[x]) / A[x]
How is the Ex ratio affected by reabsorption? By secretion?
Reabsorption results in a low extraction ratio; Secretion increases the extraction ratio.
If substance x is completely cleared from the plasma, Clearance of x= what?
Clearance x = total RPF
How is PAH handled by the kidney? What is its extraction ratio?
It is secreted by the tubule; Its extraction ratio is ~1 (0.9-0.95) or 90-95% clearance
What parameter is clearance of PAH used to estimate?
C(PAH)= Effective RPF (eRPF)
C(PAH) / (Ex Ratio PAH)= eRPF
How do you solve for RBF?
RPF/(1-Hct)
What is the commonly used endogenous indicator of GFR?
Creatinine
What characteristics of Cr make it useful as indicator of GFR?
It’s plasma concentration is constant in normal patient; it’s freely filtered, not reabsorbed, and only slightly secreted
How does Cl(Cr) compare to that of inulin and GFR.
It is slightly higher than Cl(in) and GFR, but still used as a rough estimate of GFR.
What is the relationship between plasma Cr and GFR?
They are inversely related; as GFR decreases, plasma creatinine increases.
What happens to the rate of creatinine excretion immediately after nephrectomy (GFR decreases to half)?
Urinary output of Cr likely drops to half, look at slide for other changes
