Renal Phys 10

• this can alter enzyme function and affect homeostasis, which changes the shape of proteins


  H+ ions
• normal pH =

  7.4; but acidosis and alkalosis can occur
• this rapidly adjusts pH via changes in CO2 levels


  respiratory system
• when system is in balance, P(CO2) =

  40 mmHg
• this slowly adjusts pH via changes in HCO3- levels


  renal system (kidneys)
• when system is in balance, HCO3- =

  24 mM
• except for strict vegetarians, most people have a net acid load to be excreted each day, so urine is usually ______

  acidic
• is CO2 a volatile acid?

  yes
• the carbonic acid buffering system is VERY important:

  CO2 + H2O <-> H2CO3 (carbonic acid) <-> HCO3- (bicarbonate) + H+

  this is catalyzed by carbonic anhydrase
• decreased pH = more [H+], acidic

  hydrogen ion GAIN
• ^ pH = fewer [H+], alkaline

  hydrogen ion LOSS
• hypoventilation; generation of H+ from CO2 via carbonic acid buffering system

  H+ gain
• production of nonvolatile acids from the metabolism (catabolism) of proteins and other organic molecules

  H+ gain
• losing H+ buffering capacity due to loss of HCO3- in diarrhea or other nongastric GI fluids (look at carbonic acid buffering system)

  H+ gain
• more H+ due to loss of HCO3- in the urine

  H+ gain
• utilization of H+ in the metabolism of various organic anions; anabolism

  H+ loss
• loss of H+ in vomitus; stomach acid = HCl

  H+ loss
• loss of H+ (primarily in the form of H2PO4- and NH4+) in the urine

  H+ loss
• hyperventilation (look at carbonic acid buffering system = CO2 + H2O <-> H2CO3 <-> HCO3- + H+)

  H+ loss
• most individuals reabsorb __% of bicarbonate at rest due to net acid load

  100%

  
• for every 1 bicarbonate filtered, there is 1 bicarbonate __________

  reabsorbed
• in a typical human, there is a trend toward

  acidosis and excess plasma [H+]
• (1ST METHOD) after all filtered HCO3- is reabsorbed...

  secreted H+ combines with non-bicarbonate buffer molecules like HPO42-; net gain of "new" HCO3- and goes back to normal pH

  
• (2ND METHOD) after all filtered HCO3- is reabsorbed...

  secrete H+ via ammonium from breakdown of glutamine; net gain of "new" HCO3- and goes back to normal pH

  ammonium = NH4+

  
• sufficient H+ is secreted to reabsorb all the filtered HCO3-

  renal response to acidosis
• still more H+ is secreted, and this contributes new HCO3- to the plasma as the H+ is excreted bound to nonbicarbonate urinary buffers such as HPO4(2-)

  renal response to acidosis
• tubular glutamine metabolism and ammonium excretion are enhanced, which also contributes new HCO3- to the plasma

  renal response to acidosis
• more new HCO3- than usual is added to the blood, and plasma HCO3- is increased, thereby compensating for the acidosis. the urine is highly acidic (lowest attainable pH = 4.4)

  net result of renal responses to acidosis
• rate of H+ secretion is inadequate to reabsorb all the filtered HCO3-, so significant amounts of HCO3- are excreted in the urine, and there is little or no excretion of H+ on nonbicarbonate urinary buffers


  renal response to alkalosis
• tubular glutamine metabolism and ammonium excretion are decreased so that little or no new HCO3- is contributed to the plasma from this source

  renal response to alkalosis
• plasma HCO3- concentration is decreased, thereby compensating for the alkalosis; the urine is alkaline (pH > 7.4)

  net result of renal responses to alkalosis
• cause: ^ CO2 (hypoventilation)

  result: ^ H+

  compensation: renal compensation to ^ HCO3- (new bicarb.)

  respiratory acidosis
• cause: decreased CO2 (hyperventilation)

  result: decreased H+

  compensation: renal compensation to decrease HCO3- (excrete bicarb.)

  respiratory alkalosis
• cause: ^ H+ (^ lactic acid in exercise; loss of bicarb. in diarrhea)

  result: decreased HCO3- (decreased buffer capacity)

  compensation: respiratory - more ventilation to decrease CO2

  metabolic acidosis
• cause: decreased H+ (vomiting)

  result: ^ HCO3-

  compensation: respiratory - less ventilation to ^ CO2

  metabolic alkalosis