Renal 2; Clearance

Question 1

What are the 3 basic renal units ?

Answer 1

Concentration (mg/ml)
Flow(ml/min
Load(mg/min): concentration x flow

Question 2

What 3 key factors contribute to renal concentration?

Answer 2

Pax = arterial plasma concentration of x
Pvs =venous plasma concentration of x
Ux= urine concentration of x

Question 3

What 4 key factors contribute to renal flow?

Answer 3

RBF= renal blood flow
RPF=renal plasma flow
GFR =glomerular filtration rate
V*= urine flow rate

Question 4

How do we calculate kidney input load from arterial plasma concentration and renal plasma flow?

Answer 4

Kidney Input Load = Pax * RPFa

Question 5

How do we calculate kidney output load from urine concentration, urine flow rate ,renal plasma flow and venous plasma concentration?

Answer 5

Kidney Output load = (Pvx * RPFv) + (Ux * V*)

Question 6

Principle of Conservation of mass

Answer 6

For balance, Kidney input = kidney output

Pax * RPFa = (Pvx * RPFv) + (Ux * V*)

Question 7

RPFa is greater/less than RPFv if V* is greater than 0?

Answer 7

Greater

Question 8

What are the 4 basic renal loads and do they each represent input or output?

Answer 8

(F) filtered load - tubular input
(S) secreted load - tubular input
(R) reabsorbed load - tubular output
(E)excreted load - tubular output
E = F +S-R

Question 9

How does filtered load F relate to Pax and GFR?

Answer 9

F= Pax * GFR

Question 10

How does excreted load relate to urine concentration Ux and urine flow rate V*?

Answer 10

E= UxV

Question 11

What is clearance?

Answer 11

The volume of plasma completely cleared of any substance in one minute. a flow, not a load or concentration.

Question 12

What are the minimum and maximum values of clearance?

Answer 12

min is 0. max is RPF.

Question 13

How is clearance a “virtual flow”?

Answer 13

Few substances are completely cleared from renal blood in one pass because the kidney receives about 25% of CO, and filters only 20%

Question 14

What is the general formula for clearance?

Answer 14

Load delivered to kidney = load removed from kidney in urine (But ont venous plasma; ignore because venous blood returned to body)

Cx = Ux x V*/Px

Question 15

What happens to a substance if

Cx <GFR?

Answer 15

x is filtered and reabsorbed

Question 16

What happens to a substance if

Cx = GFR?

Answer 16

x is only filtered

Question 17

What happens to a substance if

Cx > GFR?

Answer 17

x is filtered and secreted.

Question 18

What is the range of clearance values and where would the following compounds be found along that range?
glucose
proteins
inulin
creatinine
PAH
organic dyes

Answer 18

minimum Cx = 0 for glucose (Fx > 0 & Rx > 0) and proteins (Fx = 0)

mid-range Cy = GFR for inulin and creatinine (Fy > 0 & Sy = Ry = 0)

maximum Cz = RPF for PAH and organic dyes (Fz > 0 & Sz > 0)

Question 19

What kind of substance would have a clearance that would accurately measure GFR?

Answer 19

A substance that was freely filtered by the glomerulus but was neither secreted nor reabsorbed.
F = E (S=0 R =0)

Question 20

What is the clearance equal to for a substance that is filtered through the glomerulus but neither reabsorbed or secreted?

Answer 20

Cx = GFR

Question 21

What are the advantages for using inulin to determine GFR?

Answer 21

Freely filtered
neither reabsorbed or secreted
not bound to plasma proteins
not produced/consumed by kidneys
nontoxic
quantifiable

Question 22

What are the disadvantages of using inulin to measure GFR?

Answer 22

Must be infused to obtains constant measurements

Expensive

Question 23

What advantages does creatinine have over inulin?

Answer 23

constantly being infused into plasma without assistance

“Free” in that the body naturally produces it and doesn’t need be purchased

Question 24

What is the key disadvantage of creatinine?

Answer 24

Plasma concentrations of creatinine are overestimated by about 10%

Question 25

Clearance of Inulin

Answer 25

C (inulin) = U(inulin)V/P(inulin)

C(inulin) = GFR

Question 26

How is the filtration and excretion of creatinine related?

Answer 26

amount excreted is 10% less than amount filtered

Fcr ~ Ecr

Question 27

Clearance of creatinine

Answer 27

Ccr = Ucr * V*/Pcr

Ccr ~ GFR

Question 28

How is Blood-Urea-Nitrogen (BUN) related to Pcr?

Answer 28

BUN is derived from catabolism of nitrogen-containing proteins. It is roughly Pcr x 10, and is not as accurate an estimator of GFR because just eating a meal can raise BUN

Question 29

What happens when we get a decrease in functional glomeruli (renal failure)

Answer 29

Decreased GFR –> decreased Ccr –> increased Pcr

GFR * Pcr matches constant creatinine production rate

Question 30

How does clearance of para-aminohippurate equal effective renal plasma flow? What is the equation for PAH clearance?

Answer 30

PAH is filtered and secreted but not reabsorbed.
So F + S = E and R = 0.
RPF = Ux * V* / (Pax - Pvx) (EXACT)
ERPF = Ux x V*/(Pax) (APPROXIMATE)

Cpah = ERPF = Upah * V*/Papah

Question 31

What is ERPF and its relation to RPF

Answer 31

Effective Renal Plasma Flow

RPF = 1.1 ERPF (corrects for 10% of PAH not secreted in vasa recta capillaries)

Question 32

How do we convert RPF to RBF?

Answer 32

RBF = RPF / (1-Hct) where Hct is hematocrit which is typically 45%

Question 33

How do you find Filtration Fraction (FF)

Answer 33

FF = GFR/RPF = Cinulin/Cpah

Normaly FF = 20%

Question 34

Rank the following from greatest to least: (based on typical values)
GFR
RBF
RPF
V*

Answer 34

RBF&raquo_space; RPF&raquo_space; GFR&raquo_space; V*