April 20 Lectures

Danielson

acid secretion in alpha intercalated cells acidifies urine down to a minimum pH of about 4.1.  In the process a new HCO3 is produced.  these new HCO3s replace the ones lost during blood buffering of metabolic acids produced by tissues.  beta intercalated cells can secrete HCO3 into urine when there is metabolic alkalosis.

titratable acid is buffered by phosphate.  HPO4 - H2PO4. Titratable acid can be measured in the urine from the amount of sodium hydroxide needed to titrate the urine pH back to 7.4.  Can't increase much in acidosis because phosphate buffer is limited to the filtered load of phosphate and plasma phosphate is normally only 2.5 - 4.5 mg/dL. 
non-titratable acid is buffered by NH3 to NH4+ (trapped in tubule due to charge).  It is non-titratable because the high pK of ammonium means no H⁺ is removed from NH4⁺ during titration to a pH of 7.4..

glutamine synthesis is stimulated by acidosis.  iIn proximal tubule glutamine is metabolized to NH3 and 2 HCO3 (new bicarbonate).  Most important buffer for metabolic acidosis (can reach 300 mmol/day is severe acidosis).

Davenport Diagram

slope of buffer line is due to hemoglobin (major blood buffer).  steeper in polycythmia.  lower in anemia.  slope is zero for a bicarbonate solution (no buffer for changes in CO2; i.e., a buffer can't buffer itself)

bicarbonate buffer is for metabolic acidosis or alkalosis (steeper slope at higher PCO2)
hemoglobin buffer is for respiratory acidosis or alkalosis (steeper slope with higher Hb)

practice questions for acid base

Alas

Gul

Total GFR = gfr per nephron x total number of nephrons.  with nephron loss, gfr per nephron increases (increased Pc) so total GFR may be normal

1 in 9 of adults have chronic kidney disease

90% loss of GFR before uremic symptoms occur
Intact Nephron Hypothesis; remaining nephrons compensate for loss of nephrons
Trade Off Hypothesis; renal failure = increased ECF = stimulation of ANP = increased Na loss

Hb starts to decline when GFR < 40 (higher GFRs with diabetics).   treated with Epogen. 

ferretin < 100 ug/L = iron deficiency anemia

GFR is meaningful ONLY when patient is in steady state   not meaningful in acute kidney injury.