Renal Clearance and Glomerular Filtration Rate

Question 1

What is oncotic pressure?

Answer 1

Pressure generated by large molecules in solutions

Question 2

What is hydrostatic pressure?

Answer 2

Pressure exerted by liquids

Question 3

What two spaces are included in the glomerulus?

Answer 3

The vacular space and the Urinary space

Question 4

By what process does water enter the nephron?

Answer 4

Only filtration

Question 5

What is the relative concentration of glomerular blood plasma compared to ultrafiltrate?

Answer 5

Equal

Question 6

Are electrolytes and macromolecules filtered in the glomerulus?

Answer 6

Electrolytes are freely filtered, but macromolecules >10K MW are not filtered

Question 7

What drives glomerular filtration pressure?

Answer 7

Starling’s forces

Question 8

What is the average glomerular filtration rate in L/day?

Answer 8

180 L/day (both kidneys)

Question 9

What is the equation used for calculating starling forces?

Answer 9

= Kf[(Pc-Pi) - sigma(pic-pii)]

Question 10

What does the sigma represent? What is its value when calculating glomerular filtration rate?

Answer 10

Reflection coefficient for protein; =1 because protein cannot cross glomerular membrane

Question 11

What is Kf of the Starling forces equation? What is it representative of?

Answer 11

The ultrafiltration coefficient for glomerular capillaries; intrinsic pereability of glomerular capillaries

Question 12

What factors are involved in Kf? How can it be calculated?

Answer 12

Hydraulic conductivity and surface area; Kf= Lp x A

Question 13

What is the typical value of Kf when calculating glomerular filtration rate?

Answer 13

8.3 ml/min/mmHg

Question 14

What forces favor glomerular filtration?

Answer 14

Glomerular capillary hydrostatic pressure and Bowman’s space oncotic pressure

Question 15

What forces oppose glomerular filtration?

Answer 15

Bowman’s space hydrostatic pressure and glomerular capillary oncotic pressure

Question 16

What is the approximate ratio of filtration to absorption in non-renal capillaries?

Answer 16

~1:1

Question 17

What happens to the rate of fluid filtered when the glomerular capillary hydrostatic pressure is reduced?

Answer 17

It decreases

Question 18

What is the glomerular capillary hydrostatic pressure relative to most other capillaries?

Answer 18

Glomerular capillaries have about 2x more hydrostatic pressure

Question 19

What is Puf?

Answer 19

Net Starling forces

Question 20

What is the typical value of bowman’s space oncotic pressure?

Answer 20

0

Question 21

What happens to the glomerular capillary oncotic pressure over the course of the capillary?

Answer 21

Increases

Question 22

What factors can increase GFR by increasing Pcg?

Answer 22

Increased renal artery pressure, decreased afferent arteriole resistance

Question 23

What factors can decrease GFR by decreasing Pcg?

Answer 23

Increased afferent arteriole resistance and efferent arteriole resistance

Question 24

How does decreasing glomerular capillary oncotic pressure affect glomerular filtration rate? What can result in a decreased Pigc?

Answer 24

Increses it; Decreased protein metabolsim due to malnutrition, hepatic disease, or GI losses or increased protein excretion due to kidney disease?

Question 25

How does increasing the Pbs affect GFR? What could result in this increase?

Answer 25

Decreases GFR; acute obstruction- stone, enlarged prostate

Question 26

How does increasing Bowman’s space oncotic force affect GFR? What increases this value?

Answer 26

Increases; Proteinuria

Question 27

What would result in a decreased in Kf? How would it affect GFR?

Answer 27

Reduced surface area or # filtering glomeruli due to hypertension, diabetes, glomeruloclerosis; Decreases GFR

Question 28

What is renal clearance of a substance?

Answer 28

The volume of plasma from which a substance is completely removed by kidneys per unit time

Question 29

What is the typical renal clearance of glucose? What happens to the renal clearance of glucose in diabetes mellitus?

Answer 29

0; It would increase

Question 30

What is the gold standard for measuring GFR?

Answer 30

Inulin

Question 31

What is the amount of inulin filtered compared to the amount excreted?

Answer 31

Equal

Question 32

What is the rate of creatinine production compared to its rate of excretion? What is the amount filtered compared to the amount excreted?

Answer 32

Equal and equal

Question 33

How can glomerular filtration rate be calculated using inulin?

Answer 33

GFR= urine [inulin]*volume/ plasma [inulin]

Question 34

Is inulin secreted or reabsorbed?

Answer 34

No

Question 35

How can glomerular filtration rate be calculated using creatinine?

Answer 35

GFR= urine [creatinine]*volume/ plasma [creatinine]

Question 36

What is the relationship between clearance rate of creatinine and plasma concentration?

Answer 36

Inversely related

Question 37

Is creatinine secreted or reabsorbed?

Answer 37

~10% secreted by proximal tubule

Question 38

What is the normal value of glomerular filtration rate in ml/min?

Answer 38

~125 mL/min

Question 39

How does age affect the glomerular filtration rate?

Answer 39

After 40 yrs, GFR decreases by about 1 mL/min/ yr

Question 40

Where is para-amino hippuric acid made in the body?

Answer 40

It isn’t

Question 41

What does the renal clearance of PAH give an index of?

Answer 41

Renal plasma flow

Question 42

How can renal plasma flow be calculated using PAH?

Answer 42

RPF= urine [PAH]*volume/ plasma [PAH]

Question 43

Is PAH secreted or reabsorbed?

Answer 43

Vigorously secreted by the proximal tubule