Physiology

Question 1

Fluid Compartments

Calculation

Answer 1

• 60-40-20 rule (% of body weight for average person)
• 60% total body water
• 40% ICF
• 20% ECF
• 2/3 is ICF
• 1/3 is ECF (75% interstitial and 25% plasma)
• HCT (%) = 3 * [Hb] in g/dL (normal is 45%)
• RBC volume is 10% of ICF

Question 2

Glomerular Filtration Barrier

Components

Answer 2

• Fenestrated capillary endothelium (size barrier)
• Fused basement membrane with heparan sulfate (negative charge and size barrier)
• Epithelial layer consisting of podocyte foot processes (negative charge barrier)

Question 3

Renal Clearance

Calculation, Relation to GFR

Answer 3

• Cx = (Ux * V) / Px
• Cx is clearance of x in mL/min
• Ux is urine concentration of x in mg/mL
• Px is plasma concentration of x in mg/mL
• V is urine flow rate in mL/min
• if:
• Cx < GFR: net tubular reabsorption of x
• Cx > GFR: net tubular secretion of x
• Cx = GFR: no net secretion or reabsorption of x

Question 4

GFR

Calculation

Answer 4

• GFR = Clearance of inulin
• GFR = Kf [(Pgc - Pbs) - (Ogc - Obs)]
• Kf is filtration constant
• gc is glomerular capillary
• bs is Bowman space
• GFR can also be estimated by creatinine clearance. Slightly overestimates it because creatinine is moderately secreted by renal tubules

Question 5

Renal Blood Flow (RBF)

Calculation

Answer 5

RBF = eRPF / (1 - hematocrit)

Question 6

Effective Renal Plasma Flow (eRPF)

Calculation

Answer 6

eRPF = Clearance of para-aminohippuric acid (PAH)

Question 7

Filtration Fraction (FF)
(Calculation, Normal value)

Answer 7

• FF = GFR / eRPF

- FF is 20%

Question 8

Filtered Load

Calculation

Answer 8

Filtered Load (mg/min) = GFR * Px

Question 9

Excretion Rate

Calculation

Answer 9

Excretion Rate (mg/min) = V * Ux

Question 10

Reabsorption

Calculation

Answer 10

Reabsorption = filtered load - excretion rate

Question 11

Secretion

Calculation

Answer 11

Secretion = excretion rate - filtered load

Question 12

Fractional Sodium Excretion

Calculation, Interpretation

Answer 12

• FE of Na = (Usodium * Pcreatinine) / (Psodium * Ucreatinine)
• if:
• < 1% means pre-renal disease
• > 2% means acute tubular necrosis or post-renal disease
• 1-2% means either disorder

Question 13

Afferent arteriole constriction

GFR, RPF, FF

Answer 13

• Decrease
• Decrease
• No change

Question 14

Efferent arteriole constriction

GFR, RPF, FF

Answer 14

• Increase
• Decrease
• Increase

Question 15

Increase plasma protein concentration

GFR, RPF, FF

Answer 15

• Decrease
• No change
• Decrease

Question 16

Decrease plasma protein concentration

GFR, RPF, FF

Answer 16

• Increase
• No change
• Increase

Question 17

Constriction of Ureter

GFR, RPF, FF

Answer 17

• Decrease
• No change
• Decrease

Question 18

Dehydration

GFR, RPF, FF

Answer 18

• Decrease
• Decrease
• Increase

Question 19

Net Daily Acid Excretion

Calculation, Normal value

Answer 19

• Net daily acid excretion = ([titratable acids] + [NH4+] - 2*[HCO3-]) * Urine volume per day
• 70-100 meq/day