GFR/Clearance (lec 10)

Question 1

GFR tells us? (4)

Answer 1

1) measure of # of fxning nephrons
2) low GFR = sign of renal dz
3) measure drug secretion
4) grade of renal insuff

Question 2

Filtered Load (FLx) eqn?

Answer 2

FLx = (GFR)(Px)

Px = [plasma]

Question 3

Excretion Rate (ERx) eqn?

Answer 3

ERx = (Ux)(V)

Ux = [urine]
V = Urine rate

Question 4

Reabsorption rate is?

Answer 4

Rx = rate of filtrate reab by blood

Question 5

Secretion rate is?

Answer 5

Sx = rate of filtrate pulled back into the nephron from the blood

Question 6

If Rx and Sx = 0, then what?

Answer 6

ERx = FLx

Excretion rate = filtered load

Question 7

Substance filtered but NOT absorbed or secreted by nephron is measured how?

Example?

Answer 7

GFR = (Ux)(V)/Px
What goes in has to come out

Ux = [X]urine
Px = [X]plasma
V = rate of urine formation

Insulin and Creatinine are filtered this way

Question 8

Creatinine used to measure GFR, why?

Answer 8

1) creat prxn by skeletal mm @ constant rate
2) creat freely filtered, NOT reab, slight secretion
3) creat @ steady-state [ ] in blood if system is stable
4) provides estimate of GFR over preceding hours

Question 9

GFR via creat clearance equ?

Answer 9

Ccr = (Ucr)(V)/Pcr = GFR

Ccr = creat clearance
Ucr = [creat] in urine
Pcr = [creat] in plasma
V = urine flow

Question 10

Normal range for Ccr?

Answer 10

80 - 110 ml/min

Question 11

Urea comes from?

Rebsorption?

Answer 11

liver produces Urea dependent on diet/liver fxn

1/2 of filtered urea is reab

Question 12

Normal range for Blood Urea Nitrogen (BUN)?

Answer 12

9 -18 mg/dL

Question 13

BUN:Cr should be?

High tells us?

Normal tells us?

Low tells us?

Answer 13

10 - 15

High =
dehydration (↓ GFR),
up GI bleed

Normal =
acute tubular necrosis,
loss of nephrons

Low =
severe skeletal injury (↑ Cr)
liver dz (↓ BUN),
malnutrition (↓ BUN)

Question 14

Renal clearance of any solute eqn?

Answer 14

Cx = UxV/Px

Question 15

Rate of clearance of SECRETED solute compares to Ccr?

Answer 15

Csecreted > Ccr (also > GFR)

Question 16

Rate of clearance of REABSORBED solute compares to Ccr?

Answer 16

Creabsorb < Ccr (< GFR)

Question 17

Clearance ratios compared to Cinsulin:

Cx:Cins = 1

Cx:Cins < 1

Cx:Cins > 1

Answer 17

Cx:Cins = 1, x is GFR marker (not sec or reab)

Cx:Cins < 1, x not filtered, or both filt and reab

Cx:Cins > 1, x filtered and secreted

Question 18

Para-aminohippurate (PAH) is?

Answer 18

IV infused marker
w/ 100% clearance from blood,
estimates rate of nephron plasma flow (RPF)

Question 19

Calculate Cpah how?

Answer 19

Cpah = (Upah)(V)/Ppah

Question 20

Use Cpah to estimate RBF how?

Answer 20

RBF = RPF / (1-Hct)

*get RPF value from Cpah eqn -> RPF=Cpah