04 Renal Physiology II

Function Measurements

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• actual calculation

• GFR: main number for kidney healthiness

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• 40% going across glomerulus, 60% leaving kidney

• actual calculation

• GFR: main number for kidney healthiness

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• how much Na going across glomeruli per min

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• urine flow: how much urine kidney making

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• urine flow rate: how much urine pt makes

Clearance

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• urine concentration, urine flow rate , plasma concentration

• kidney cleared 5 mole of Na OR

• kidney cleared 1L of blood of Na

GFR

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• inulin

• creatinine

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• all filtered inulin goes out of kidney

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• naturally clearing, easier to do

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• Volume flow cumbersome to determine

• special formula to use

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• amount in urine = amount made in muscles

• not a linear, straight line relationship

• plasma Cr concentration, not urine concentration

• use clearance equation to calculate GFR if given urine/plasma concentration and urine flow

RPF

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• small amount goes to CT

• everything in goes out, none in the efferent

• calculate amt of blood filtered of PAH (clearance), one can find amt of blood enter kidney

RBF

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• HCT = bottom red

Others

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Meds

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• FF same: still filtering same percentage of blood

• pt can go into renal failure/heart failure

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• Ang II: constrict efferent, increase GFR, decrease RBF

Secretion and Absorption

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• if filtered not = excretion, some must be either secreted or reabsorbed

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• if put in 10 grams, must excrete 10 grams, otherwise accumulate

Normal:

• 5 in, 5 out, 4 plasma concentration

• insult: can't excrete, 5 in, 2 out, plasma concentration go up to 6

  
• new steady state, 5 in, 5 out, 6 plasma

• new steady state concentration higher than original steady state

• e.g. hyperkalemia, excreting same amount taking in

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• filtered load: GFR x plasma concentration for urea is same

• fractional excretion: excretion/filtered load, filtered load fallen, amt excreted is same

• 5 g filtered, 1 secreted, fractional excretion: 1/5

• renal failure, GFR fallen

• 2 g filtered, 1g excreted, fractional excretion 50%

Practice Questions

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• clearance of inulin = GFR