Unit 2, L11 Renal Clearance Flashcards
What is the one input which we consider the kidney input load?
The arterial plasma load
What are the three output loads
Venous, ureter, and lymph
What is the definition of a load
A load of any substance is always the product of its concentration times the flow
Equation for load
Load (mg/min) = concentration (mg/mL) * Flow (mL/min)
Pax is what
Arterial plasma concentration of substance X
PVx is what
Venous plasma concentration of substance X
UX is what
Urine concentration of substance X
Lx is what
Renal lymph concentration of substance X
RBF stands for
Renal blood flow (mL/min)
RPF stands for
Renal plasma flow (mL/min)
GFR stands for
Glomerular filtration rate (mL/min)
RLF stands for
Renal lymph flow (mL/min)
V with a dot above it stands for
Urine flow rate (mL/min)
C stands for
Clearance, mL/min
[P] stands for
Concentration in plasma, in mg/mL
[U] stands for
Concentration in urine, mg/mL
Normal value for GFR
120-125 mL/min
Normal value for RPF
660 mL/min
Normal value for RBF
1200 mL/min
Renal input load needs to equal renal output load, what is the equation for this, when adding in all the individual loads of the kidney?
Arterial plasma load X = Ureter load X + Venous load X + Lymphatic load X
Pax * RPFa = Ux * V (dot) + Pvx * RPFv + Lx *RLF
What adjustments can we make to the mass balance equation? and what is the new equation?
Ignore the lymphatic node and venous load. New equation is Pax * RPFa = Ux * V (with a dot)
What is the definition of clearance
The volume of plasma completely cleared of any substance in one minute
What if the clearance equation
Cx = Ux * V (dot) / Px
What is the range of values for clearance?
From 0 mL/min to 660 mL/min, aka RPF
Filtered load of substance X is the product of
Glomerular filtrate flow times the concentration of X in the plasma
Excreted load of substance X is the product of
Urine flow times the concentration of X in the urine
Ex (mg/min) = Ux (mg/mL) * V (dot) urine (mL/min)
Clearance is the _________ rate divided by the __________ concentration
Excretion rate divided by the plasma concentration
Cx (mL/min) = Ex (mg/min) / Px (mg/mL)
What is the GFR
Volume of filtrate per unit time in the kidney, it is the rate of volume going through the glomerulus.
What is a good index of renal function?
GFR
Why can we use inulin?
Because inulin in the plasma is freely filtered by the glomerulus, and its neither secreted from nor reabsorbed into the renal capillary blood, so the clearance of this substance is an accurate measurement of GFR
What is the clearance equation for inulin
F = E (since S and R = 0)
Px (mg/mL) * GFR (mL/min) = Ux (mg/mL) * V (dot) urine (mL/min) and X is inulin
Clearance of inulin will equal what
GFR
What are the advantages of inulin
It is freely filtered, neither reabsorbed nor secreted
It is not bound by plasma proteins and its not produced or consumed by the kidneys
It is nontoxic
It is easily and accurately quantified in plasma and urine (measurable)
Disadvantages of Inulin
Must be infused to obtain constant blood titers
It is expensive
What is creatinine
An end-product of muscle metabolism
Amount filtered and excreted of creatinine
Amount creatinine filtered < amount creatinine excreted (by 10%), so F < E
Advantages of creatinine
It is freely filtered, its not bound to any plasma proteins and its not produced or consumed by the kidneys
It is easily and accurately quantified in plasma and urine
It is constantly being “infused” to obtain constant blood titers
It is free and doesn’t need to be purchased
Disadvantages of creatinine
It is not reabsorbed but 10% is secreted, but this is corrected by the over estimation (10%) of the plasma concentration of creatinine
What is the relationship between GFR and plasma creatinine
Inverse relationship, so the more GFR, the less plasma creatinine and vice versa
If the GFR falls from 120 to 60 mL/min, what will happen to the plasma creatinine concentration
Increase from 1 to 2 mg/dL to keep filtration of creatinine and its excretion equal to production rate
What are the three markers for GFR?
Plasma (serum) creatinine
Blood urea nitrogen (BUN)
BUN:Creatinine ratio
What do you have to keep in mind for creatinine
A young muscular man will have a higher plasma creatinine than an older woman with reduced muscle mass
Where does BUN come from
Break down product of muscle catabolism, sign of metabolism
Normal ranges for BUN
9 to 18 mg/dL
What is the ratio between BUN and creatinine
10:1 ratio
What can the BUN:creatinine ratios be indicitive of
Volume contraction
Renal plasma flow is estimated by measuring what
PAH, which is infused intravenously
Advantages of PAH
Freely filtered, not reabsorbed, it is secreted and 90% is excreted, and its nearly completely cleared from all the plasma
What is the disadvantage of PAH
10% of PAH is retained in the venous system
How can we cancel the venous sample out of the equation for renal plasma flow
The equation is RPF = Upah * V (dot) / (Papah - Pvpah) but its hard to sample the renal venous blood so we use the effective renal plasma flow (ERPF) to cancel the venous sample
What is the equation for clearance of PAH and what is the normal value for ERPF
Cpah (mL/min) = U pah * V (dot) / Papah, and since Cpah = ERPF, its about 660 mL/min
PAH is only ERPF at what kind of concentrations
Low concentrations
If Cx = GFR, what is happening with F, E, R, and S, and what example did we learn about in class?
If Cx = GFR, then X is only F and E, not R or S. This is inulin
If Cx < GFR, what does that mean for F, E, R, and S?
X is F, E, and R, not S
If Cx > GFR, what does that mean for F, E, R, and S?
X is F, E, and S, not R
If clearance of X is zero, what does that mean for F, E, R, and S?
If X is freely filtered and totally reabsorbed, so only F and R, OR there is no F, its not filtered at all
What is the filtration fraction
The ratio between the GFR and the RPF, the fraction of the RPF that is filtered by the glomerular capillaries
What is the value for a normal FF
About 20%
