acid base balance Flashcards
where is bicarbonate reabsorbed
90% in the pct, the rest in the dct
what other buffers are there apart from bicarbonate
urate phosphate creatinine beta hydroxybutyrate proteins haemoglobin
what is fraction of inspired oxygen
the proportion of air that is breathed in which is oxygen
eg room air is 20% which is 0.2
what is a healthy p/f ratio
12/ 0.2 = 60
what type of blood is the anion gap calculated from
venous
what are the features of a normal anion gap acidosis
loss of bicarb
therefore chlorine is retained by the kidneys in order to maintain neutrality of the serum
what is renal tubular acidosis
failure of kidneys to excrete acid causes blood acidosis
will not cause an increased anion gap
hypercholaemic
either failure to reabsorb bicarb or failure to secrete acid
what type of acidosis would anion gaps be used for
metabolic only
what is normal anion gap
16
what two substances will cause an increase anion gap when ingested
methanol
ethylene glycol
what gap does renal failure cause
increased gap
what does the kidney do to bicarbonate
reabsorbs filtered bicarb
regenerates bicarb consumed by buffering
why does diarrhoea cause acidosis
for every bicarb ion released into the gut one H+ is released into the ECF
This process is increased in diarrhoea
how can the kidneys correct for metabolic acidosis
only if non renal origin and the kidneys are working
secrete more acid into the urine and make new bicarb
what is pf ratio
the arterial oxygen partial pressure / fraction of air that is oxygen
normal arterial oxygen is approx. 12
room air is approx. 20% O2
so PF = 12/0.2= 0.6 or 60%
where is bicarbonate reabsorbed
PCT (90%) , DCT and collecting duct(10%)
what is titratable acid
any acid except for ammonium
what is distal renal tubular acidosis
failure to concentrate H+ in the distal tubule
what is proximal renal tubular acidosis
impairs PCT reabsorption of bicarbonate
most common in children
what is hyperkalaemic renal tubular acidosis
reduction in aldosterone inhibits NH3 production
most common in adults
what factors regulat renal bicarb handling
PCO2, H+, volume of ECF, angiotensin 2, aldosterone, potassium
what amino acid is involved in ammonium excretion
glutamine
what acid excretion increases greatly during acidosis
ammonium
titratable acid excretion is relatively constant
what is glutamine turned into in ammonium secretion
alpha keto glutarate
