Equations

Question 1

Filtered Load

Answer 1

FL = (GFR {glomerular filtration rate}) * (Px {plasma concentration of x})

Note that each ion has a percent of total circulating volume that is bound to protein, which cannot be filtered. Thus you would have to determine the fraction of FL that is actually being filtered (free, unbound ions)

Question 2

Urinary Excretion

Answer 2

Urinary Excretion = filtered load - amount reabsorbed + amount secreted

Question 3

Tubular Reabsorption

Answer 3

Tubular Reabsorption = amount filtered - amount excreted + amount secreted

Question 4

Peritubular Secretion

Answer 4

Peritubular Secretion = amount excreted + amount reabsorbed - amount filtered

Question 5

Glomerular Filtration

Answer 5

Glomerular Filtration = amount excreted + amount reabsorbed - amount secreted

Question 6

Urine Excretion Rate of x

Answer 6

Urine Excretion Rate of x = [Ux {urine concentration of x}] * (V {Urine Flow Rate})

Question 7

Clearance of x

Answer 7

Cx = ([Ux {urine concentration of x}] * V {urine flow rate}) / ([Px] {plasma concentration of x})

Question 8

Filtration Fraction

Answer 8

FF = GFR {glomerular filtration rate} / RBF {renal blood flow}

Note: RBF is synonymous with RPF (renal plasma flow)

Question 9

Glomerular Filtration Rate

Answer 9

GFR = ([Ux {urine concentration of x}] * V {urine flow rate}) / [Px {plasma concentration of x}]

Where ‘x’ is either inulin or Creatinine

Question 10

Effective Renal Plasma Flow

Answer 10

Effective RPF = ([Upah {urine concentration of PAH}] * V {urine flow rate}) / [Ppah {plasma concentration of PAH}]

PAH: Para-aminohippuric Acid

Question 11

Clearance Ratio

Answer 11

CR = C(x) {clearance of x} / C(inulin) {clearance of inulin}

Question 12

Reabsorption/Secretion Rate

Answer 12

Reabsorption/Secretion Rate = FL (filtered load) - Excretion Rate

= (GFR * [Px]) - ([Ux] * V)

If (+) = Net reabsorption
If (-) = Net secretion

Question 13

Starling Equation GFR

Answer 13

GFR = Kf * Puf {capillary ultrafiltration pressure}

GFR = Kf {filtration coefficient} [(Pgc {glomerular hydrostatic pressure} - Pbs {bowmans hydrostatic pressure}) - (“pi”gc {glomerular oncotic pressure} - “pi”bs” {bowmans oncotic pressure})]

Question 14

Serum (plasma) Osmolarity (hard way)

Answer 14

(2 * [Serum Na+]) + ([Serum Glucose]/18) + (BUN / 2.8)

Question 15

Serum (plasma) Osmolarity (easy way)

Answer 15

2 * [serum Na+]

Question 16

Capillary Ultrafiltration Pressure

Answer 16

Puf = Pgc - Pbs - “pi”gc