Equations

Question 1

filtered load/rate (mg/min)

Answer 1

= (Px) x GFR

amount of substance in plasma that is filtered at glomerulus per unit of time

Question 2

excretion rate (mg/min)

Answer 2

= (Ux) x V

amount of substance excreted into urine per unit time

Question 3

Renal Clearance (ml/min)

Answer 3

= (U x V) / P

*use same formula for RPF and GFR

Question 4

Clearance ratio

Answer 4

Cx / GFR
1 = filtered; clearance = GFR
less than 1 = filtered and reabsorbed
greater than 1 = filtered and actively secreted
0 = not filtered or filtered and 100% reabsorbed

Question 5

Filtration Fraction

Answer 5

GFR / RPF
normal ~ 20%
amount of renal plasma flow that becomes GFR

Question 6

Net filtration pressure

Answer 6

Kf (PG + πBS) - (πG + PBS)

Kf: determined by SA and permeability

Question 7

Renal Blood Flow (RBF)

Answer 7

RPF / (1 - Hct)
OR
RPF / PV

Question 8

Glomerular Filtration Rate (GFR)

ml/min

Answer 8

(U x V) / P
inulin
*GFR must be a freely filtered substance that is not reabsorbed, secreted, metabolized, or synthesized = creatinine or inulin

Question 9

Renal Plasma Flow (RPF)

ml/min

Answer 9

(U x V) / P
PAH
filtered and avidly secreted

Question 10

V of body fluid compartment

PV, ECFV, TBW

Answer 10

Q / (Q / V)
Q = quantity injected
(Q/V) = concentration of probe in fluid
*make sure to correct for excretion

Question 11

ISFV

Answer 11

ECFV - PV

Question 12

ICFV

Answer 12

TBW - ECF

Question 13

plasma osmolarity

Answer 13

(plasma Na x 2) + (glucose / 18) + (BUN / 2.8)

Question 14

Mass flow

ml or mEq or mg / min

Answer 14

concentration / rate of volume flow

expression of solute movements as a function of time

Question 15

Vol. loop of Henlee (VL)

ml/min

Answer 15

(GFR x Px) / TFx

Question 16

Reabsorption

ml/min

Answer 16

GFR - VL

Question 17

[H+] nEq/l

Answer 17

24 x (PCO2 / HCO3)
OR 
easy method
80 - decimal digits of pH 
*less accurate as get away from 7.4

Question 18

pH

Answer 18

6.1 + log ( [HCO3] / .0301 PCO2)

Question 19

plasma anion gap

Answer 19

Na - (Cl + HCO3)

Question 20

urine anion gap

Answer 20

(Na + K) - Cl

indirect estimate of urinary NH4

Question 21

osmolar clearance (Cosm)

Answer 21

(UF x Uosm) / Posm

Question 22

free water clearance (CH2O)

Answer 22

UF x ( 1 - (Uosm / Posm)
OR
UF - Cosm

Question 23

fractional excretion of bicarbonate (FEHCO3)

Answer 23

( UHCO3 x PCr) / ( PHCO3 x UCr )

Question 24

FeNa (fractional excretion of Na)

Answer 24

( UNa x PCr ) / ( PNa x UCr )

Question 25

blood volume

Answer 25

PV/ (1 - Hct)