Renal Clearance

Question 1

What are the units of clearance?

Answer 1

Volume per unit time

Question 2

What are the 3 processes in the nephron?

Answer 2

Glomerular Filtration
Resorption of the Substance into Blood
Secretion of the Substance into Tubule

Question 3

What are the renal units for concentration?

Answer 3

mg/mL

Question 4

What are the renal units for flow?

Answer 4

mL/min

Question 5

What are the renal units for load?

Answer 5

mg/min

Question 6

Pax

Answer 6

Concentration x in Arterial Plasma

Question 7

Pvx

Answer 7

Concentration x in Venous Plasma

Question 8

Ux

Answer 8

Concentration x in Urine

Question 9

RBF

Answer 9

Renal Blood Flow

Question 10

RPF

Answer 10

Renal Plasma Flow

Question 11

GFR

Answer 11

Glomerular Filtration Rate

Question 12

V

Answer 12

Urine Flow Rate

Question 13

What is the kidney input load equal to?

Answer 13

Pax + RPFa

Question 14

What is the kidney output load equal to?

Answer 14

(Pvx * RPFv) + (Ux * V)

Question 15

If urine flow rate V>0mL/min then how are the values of the RFPa and RFPv affected?

Answer 15

RPFa > RPFv

Question 16

What is the equation for conservation of mass in regards to renal function?

Answer 16

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

Question 17

What are the loads that enter the tubule?

Answer 17

F - filtered load

S - secreted load

Question 18

What are the loads that leave the tubule?

Answer 18

R - reabsorbed load

E - excreted load

Question 19

What is the filtered load equal to?

Answer 19

Pax * GFR

Question 20

What is the excreted load equal to?

Answer 20

Ux * V

Question 21

What is clearance?

Answer 21

It is defined as the volume of plasma completely cleared of any substance in one minute

Question 22

What is the range of clearance?

Answer 22

0 to RPF (maximum)

Question 23

What is the RPF in terms of the cardiac output?

Answer 23

RPF is around 25% of the cardiac output

Question 24

How much of the RPF does the kidney filter?

Answer 24

20% -> this is the GFR

Question 25

What is the formula for clearance?

Answer 25

Cx = Ux * (V/Px) Px - plasma concentration of x

Question 26

Why is the venous return ignored in clearance?

Answer 26

Venous blood is returned to the body

Question 27

What happens if Cx < GFR?

Answer 27

Substance x is filtered and reabsorbed

Question 28

What happens if Cx = GFR?

Answer 28

x is only filtered

Question 29

What happens if Cx > GFR?

Answer 29

x is filtered and secreted

Question 30

What is the clearance range for glucose and proteins?

Answer 30

Cx = 0 usually

Question 31

What is the clearance range for inulin and creatinine?

Answer 31

Cx = GFR

Question 32

What is the clearance range for PAH and organic dyes?

Answer 32

Cx = RPF

Question 33

What substances can give an accurate measurement of GFR?

Answer 33

Substances that are filtered by the glomerulus but neither secreted nor reabsorbed would be an accurate measurement of the GFR. F = E in this case as S and R = 0

Question 34

What are the advantages of using inulin to determine GFR?

Answer 34

- It is neither reabsorbed or secreted so S and R = 0 - Neither produced or consumed by kidneys - Easily measurable - Nontoxic

Question 35

What are the disadvantages to using inulin to determine GFR?

Answer 35

- It must be infused constantly | - It is expensive

Question 36

What are the advantages to using creatinine to determine GFR?

Answer 36

- It is a natural metabolic product of skeletal muscle metabolism - Not reabsorbed so R=0 - Neither produced or consumed by kidneys - Nontoxic - Easily measured - Constantly being infused naturally - "Free" so it is cheap

Question 37

What are the disadvantages of using creatinine to determine GFR?

Answer 37

-10% is secreted so S>0

Question 38

Which method of measuring GFR is more accurate?

Answer 38

Inulin

Question 39

Which method of measuring GFR is more accessible?

Answer 39

Creatinine

Question 40

How does the value of the GFR measured by the creatinine method differ from the true value?

Answer 40

It is overestimated by around 10%

Question 41

What is BUN and how is it used?

Answer 41

It is the blood urea nitrogen and it is used to roughly estimate GFR.

Question 42

What is the relationship between GFR and PCr?

Answer 42

As the GFR decreases, the PCr will increase as the excretion is falling while the production rate remains constant.

Question 43

Why is PAH a good estimation for RPF?

Answer 43

It is not normally found in the body and it is freely filtered and secreted by the proximal tubule and more is removed than what is filtered. R=0 as none is reabsorbed.

Question 44

What is the RPF equal to?

Answer 44

RPF = RBF * (1-Hematocrit)