Wilson

Question 1

Respiratory acidosis

Answer 1

• caused by HYPOventilation
• increases pCO2
• point on normal buffer slope BELOW ph 7.4

Question 2

respiratory alkalosis

Answer 2

• caused by HYPERventilation
• decreases pCO2
• Point on normal buffer slope above pH 7.4

Question 3

Metabolic acidosis

Answer 3

• loss of HCO3-
• point on 40 torr isobar BELOW pH 7.4

Question 4

Metabolic alkalosis

Answer 4

• Increases in HCO3- conc
• point on 40 torr isobar ABOVE pH 7.4

Question 5

Compensation of the acid-base balance

Answer 5

goal is to maintain balance of HCO3-/pCO2

• Respiratory compensation
  
  • hypo or hyperventilation regulates pCO2
    
    • RAPID (HOURS)
• Renal compensation
  
  • regulation of HCO3- conc
  • regulation of H+ EXCRETION
  • SLOW (days)

Question 6

role of kidney in regulation of pH

Answer 6

• kidneys regulate H+ excretion and HCO3- reabsorption
  
  • H+ ions are removed by binding to filtered buffers or binding to NH3
  • ELIMINATION of HCO3- in urine is equivalent to ADDING H+ to the body
    
    • cannot eliminate the H+ load unless virtually all filtered HCO3- is reabsorbed

Question 7

describe the secretion of H+ by renal tubule cells

Answer 7

• Proximal acidification
  
  • Na+/K+ ATPase generates a sodium potassium electrochemical gradient on the basolateral membrane
  • on the luminal membrane there is an Na+/H+ exchanger that uses electrochemical gradient to move H+ outside of the tubule cell
• Distal acidification in the collecting duct
  
  • insertion of ATPase into luminal membrane stimualted by LOW pH (more protons are pumped out)
    
    • high pH stimulates recycling of ATPase back to the cytoplasm

Question 8

describe the reabsorption of bicarbonate in the PROXIMAL TUBULE

Answer 8

1. H+ secreted into tubule lumen
2. reacts with HCO3- in filtrate –> forms CARBONIC ACID
3. Carbonic anhydrase converts carbonic acid to H2O and CO2
4. H2O and CO2 diffuse into renal tubular cell
5. carbonic anhydrase converts H2O and CO2 to carbonic acid
6. Carbonic acid dissociates, H+ exported to tubule lumen and HCO3- exported to blood

NET = movment of NaHCO3 FROM filtrate to BLOOD

Question 9

role of H2PO4- (filtered buffer)

Answer 9

• secreted H+ is buffered in filtrate and the buffer is excreted
• phosphate typically major non-bicarbonate urinary buffer
• H+ secretion increases conc of H+ in tubule lumen
  
  • SHIFTS EQUILIBRIUM LEFTWARD
    
    • drives fromation of H2PO4-, ELMINATED IN URINE
• Ability to excrete H+ as H2PO4 limited by
  
  • amount of HPO4- in filtrate
  • requirement of body to retain phosphate

Question 10

Net result of formation of H2PO4- excretio in urine

Answer 10

One H+ eliminated

one NEW HCO3- formed and added to the blood

Question 11

what is titratable acid

Answer 11

• it is a measure of H+ excreted in urine as UNDISSOCIATED WEAK ACID
  
  • generally H2PO4- (most abundant)
• NORMAL = 0 to 20mmol/day
• acidosis = 40mmol/day

WILL SEE OTHER ACIDS DURING DIFFERENT PATHOLOGIC STATES:

• beta-hydroxybutyric acid - during ketoacidosis
• lactic acid - during lactic acidosis

Question 12

Excretion of H+ as NH4+

Answer 12

• First step is generation NH4+ within renal tubules cells
  
  1. kidney expresses GLUTAMINASE
  2. converts glutamine to glutamate
  3. glutamate then CONVERTED to ALPHA-KETOGLUTARATE by GLUTAMATE DEHYDROGENASE
     
     • glutamate metabolism ultimately yeilds 2 HCO3-
• NH4+ exported to tubular lumen
• HCO3- released to the blood

NET = excretion of protrons into lumen and addition of new molecules of HCO3- to the blood

Question 13

describe the regulation of H+ excretion

Answer 13

• Rate of H+ secretion is pH DEPENDENT
  
  • reduce pH ACTIVATES Na+/H+ antiporter and H+-ATPase
    
    • increases the amount of proton is pushed into lumen

Question 14

describe the effects of H+ excretion during ACIDOSIS STATE

Answer 14

• DURING ACIDOSIS
• H+ secretion INCREASED
• all HCO3- Reabsorbed
• substantial titratable acid excreted
• NH4+ production INCREASED
  
  • increased glutamine uptake/glutaminase activity
  • increased NH4+ excretion in urine

Question 15

describe the effects of H+ excretion DURING ALKALOSIS

Answer 15

• DURING ALKALOSIS
  
  • H+ secretion insufficient to allow HCO3- reabsorption
    
    • HCO3- SECRETED IN URINE
  • B-Type intercalated cells of collecting duct ACTIVELY SECRETE BICARBONATE into tubular lumen
  • no titratable acid or ammounium ions excreted in urine