Acid/Base Balance Flashcards
what does pH measure
free hydrogen ion concentration
alkalosis
high blood pH
acidosis
low blood pH
HCO3/CO2 buffer system
pH = HCO3 / CO2
what is pCO2 regulated by
lungs
what is HCO3 regulated by
kidneys
metabolic acidosis
low HCO3
loss of HCO3 or gain of acid
metabolic alkalosis
high HCO3
gain of HCO3 or loss of acid
respiratory acidosis
high pCO2
hypoventilation
respiratory alkalosis
low pCO2
hyperventilation
what does TCO2 measure
proxy for HCO3
measures metabolic a/b abnormalities
standard base excess
estimates how much acid/base is missing/in excess
what does SBE = 0 indicate
normal health
what does SBE > range indicate
alkalosis
what does SBE < range indicate
acidosis
when does respiratory compensation occur
immediately
when does metabolic compensation occur
starts in hours, finishes in days
does compensation completely normalize pH
NO
what is a mixed a/b abnormality
both respiratory and metabolic abnormalities
can mixed abnormalities normalize pH
YES
causes of respiratory acidosis/alkalosis
lung or brain/nervous system disease
causes of metabolic alkalosis
loss of acid - renal or gastric
gain of bicarb - iatrogenic
causes of metabolic acidosis (high AG)
D: diabetic ketoacidosis
U: uremic acidemia
E: ethylene glycol toxicity
L: lactic acidosis
causes of metabolic acidosis (normal AG)
loss of bicarbonate - renal or intestinal
anion gap
unmeasured anions
AG = (Na + K) - (HCO3 + Cl)
what is the function of the kidneys in acid/base balance
- reabsorb filtered bicarbonate
- excrete daily acid load (carnivores)
- excrete excess bicarbonate (herbivores)
is losing a bicarbonate the same as gaining a hydrogen ion
YES
where does the majority of HCO3 reabsorption occur
PCT and loop of henle
(constant amount)
where does the regulation of HCO3 reabsorption occur
DCT
is HCO3 directly reabsorbed
no - does not cross luminal membrane
combines with H+ and undergoes carbonic anhydrase reaction to form CO2 + H2O which transports into tubule epithelial cell, then undergoes another CA reaction to reform HCO3
HCO3 gets reabsorbed and H+ gets pushed back out to the tubule lumen
is HCO3 reabsorption acid/base neutral
YES
for every 1 HCO3 filtered at glomerulus there is 1 HCO3 getting reabsorbed
what drives HCO3 reabsorption
gradients established by Na/K ATPase
how does the DCT regulate HCO3 reabsorption
two types of intercalated cells (type A and B)
intercalated A cells
push acid (H+) out into lumen
reabsorbs bicarb (HCO3) into blood
intercalated B cells
push bicarb (HCO3) out into lumen
reabsorbs acid (H+) into blood
if H+ excretion = HCO3 filtration at glomerulus, what is the net HCO3 loss/gain
NO loss or gain
for every 1 H+ excreted –> 1 HCO3 gets reabsorbed
so if H+ excretion is equal to HCO3 filtration, then no net change in A/B balance
how does H+ excretion change in ALKALOSIS
do not want to reabsorb all HCO3 because there is already excess in the blood
decrease H+ excretion until H+ excretion < HCO3 filtration
causes net loss of HCO3
how does H+ excretion change in ACIDOSIS
need to generate new bicarbonate to raise pH
increase H+ excretion until H+ excretion > HCO3 filtration
excess H+ cannot be freely excreted –> must bind to buffers to avoid changing urine pH
urinary buffers
- phosphate
- ammonium
how does phosphate help during acidosis
combines with free H+ in tubule for excretion
allows reabsorption of a new HCO3 ion –> net gain HCO3 –> increases pH
how does ammonium help during acidosis
NH4 is produced by glutamine metabolism in PCT –> metabolism gets up-regulated during acidosis
every 1 NH4+ excreted = 1 H+ excreted = 1 HCO3 generated –> increases pH
how does the kidney respond to alkalemia
- decrease H+ excretion by inhibiting intercalated A cells
- increase HCO3 excretion by stimulating intercalated B cells
- down regulate glutamine metabolism
what is acute kidney injury
decrease in GFR –> kidney failure
what acid/base changes are common in AKI in carnivores
metabolic acidosis w/ high anion gap
protein metabolism –> increase acids –> unable to excrete daily load
what acid/base changes are common in AKI in herbivores
metabolic alkalosis
carbohydrate metabolism –> increase bicarb –> unable to excrete daily load
OR
metabolic acidosis w/ high AG due to uremic acid accumulation
sign of renal tubular acidosis
metabolic acidosis w/ normal AG
NOT in kidney failure - GFR is normal
