Acid Base Balance Flashcards
what is the average pH of blood?
7.4
what is the pH of ECF?
7.4
what effect can acidosis have on the CNS?
depression of the CNS
what effect can alkalosis have on the nervous system?
over excitability
how can the kidneys control plasma bicarbonate concentration?
reabsorb HCO3
can add new HCO3 to the blood
what does kidney control of bicarbonate concentration depend on?
hydrogen secretion into the tubule
how much hydrogen is filtered into the tubular fluid at normal pH?
very few
there aren’t many in the plasma
what cells secrete hydrogen ions into the filtrate?
proximal tubule
distal tubule
collecting duct
how much bicarbonate is present in normal filtrate?
a lot - as they are freely filtered
how are bicarbonate ions taken up by tubular cells?
combine with hydrogen in the tubular fluid to form carbonic acid, dissociates into CO2 and H2O which enter the cell by diffusion
what transporter secretes hydrogen ions into the tubular fluid normally?
the sodium hydrogen anti-porter
how is bicarbonate moved out of the tubular cell into the interstitial fluid?
H2O + CO2 reform carbonic acid, dissociates into bicarbonate + H
leaves by the sodium bicarbonate co transporter
when bicarbonate in the tubular fluid is low due to buffering an acidosis, what is the next most plentiful buffer available?
phosphate
how does phosphate act as a buffer in the tubular fluid?
binds to hydrogen ions forming an acid phosphate which is excreted from the body in the urine
what acts as a buffer in acidosis when all bicarbonate and phosphate has been used up?
ammonia
how does ammonia act as a tubular buffer?
combines with hydrogen to form ammonium ions which are excreted in urine
how is ammonia formed?
metabolism of glutamine (amino acid) by glutaminase to form ammonia
what is compensation?
restoration of pH regardless of what happens to bicarbonate and pCO2
what is correction of an AB disturbance?
restoration of pH, bicarbonate and pCO2 to normal
how can a blood gas analysis be visualised and plotted?
on a davenport diagram
what is a respiratory acidosis?
retention of CO2 by the body
name three possible causes of respiratory acidosis
chronic bronchitis
chronic emphysema
chest injuries
what does a respiratory acidosis cause?
rise in H+ and HCO3
when is it classified as an uncompensated respiratory acidosis?
pH <7.35
pCO2 >45
how is a respiratory acidosis compensated?
by the kidneys
CO2 retention stimulates H+ secretion into the filtrate = excreted
all bicarbonate reabsorbed
produces bicarbonate and excretes phosphate + ammonium
how is a respiratory acidosis corrected?
restoring normal ventilation
what is a respiratory alkalosis?
excessive removal of CO2 by the body
name two possible causes of respiratory alkalosis
altitude
hyperventilation
what happens as a result of a respiratory alkalosis?
hydrogen and bicarbonate concentrations fall
what indicates an uncompensated respiratory alkalosis?
pH >7.45
PCO2 <35
how is a respiratory alkalosis compensated?
bicarbonate excreted in the urine
no more bicarbonate generated
reduced H+ secretion
how is a respiratory alkalosis corrected?
restoration of normal ventilation
what is a metabolic acidosis?
excess H+ from any source other than CO2
what indicates an uncompensated metabolic acidosis?
pH <7.35
low HCO3
how is a metabolic acidosis compensated?
ventilation increased to blow off more CO2
how is a metabolic acidosis corrected?
more bicarbonate generated by the kidneys and acidic urine excreted
normalise ventilation
what is metabolic alkalosis?
excessive loss of H+ from the body
what indicates an uncompensated metabolic alkalosis?
pH >7.45
high HCO3
how is a metabolic alkalosis compensated?
slowed ventilation to retain. CO2
how is a metabolic alkalosis corrected?
HCO3 excreted and no more generated
falls to normal
