04 Renal Physiology II

  • actual calculation
  • GFR: main number for kidney healthiness

  • 40% going across glomerulus, 60% leaving kidney

  • actual calculation
  • GFR: main number for kidney healthiness

  • how much Na going across glomeruli per min

  • urine flow: how much urine kidney making

  • urine flow rate: how much urine pt makes

Clearance

  • urine concentration, urine flow rate , plasma concentration

  • kidney cleared 5 mole of Na OR
  • kidney cleared 1L of blood of Na

GFR

  • inulin
  • creatinine

  • all filtered inulin goes out of kidney

  • naturally clearing, easier to do

  • Volume flow cumbersome to determine
  • special formula to use

  • 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

  • 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

  • HCT = bottom red

Others

Meds

  • FF same: still filtering same percentage of blood
  • pt can go into renal failure/heart failure

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

Secretion and Absorption

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

  • 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

  • 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