Chempath 3: Acid base disorders Flashcards
Which acid/base disorder do you get in pyloric stenosis ?
Hypokalaemic hypochloraemic Metabolic Alkalosis
What happens to HCO3 in Pyloric stenosis and why ?
HCO3 increases because of relative fluid loss in vomiting. Also carbonic acid dissociates and only the H+ ions are lost, HCO3 is retained.
H+ further decreases due to exchange for intracellular K+ to adjust the hypokalaemia.
normal range for [H+]
35-45 mol/l in ECF
calculation for pH
low 1/[H+]
list the different types of buffering systems in the body
bicarbonate - H+ + HCO3- –> H2C03 (ECF, globular filtrate)
haemoglobin - H+ + Hb- –> HHb (RBC)
phosphate - H+ + HPO4 - –> H2PO4 (RTF, IC)
also protein and bone
what is the most important buffering system in the human body
Bicarbonate
how are h+ ions excreted
H+ + HCO3- –> H2CO3 –> CO2 + H20
as you buffer H+ you use up bicarbonate ions
bicarbonate buffer is only effective in the short term
to maintain homeostasis, kidney needs to excrete H + ions and regenerate bicarb ions
Bicarbonate is regenerated through the production of carbonic acid
H + ions cannot pass through the membrane by itself - Na+/H+ exchange needed
3 causes of metabolic acidosis
increased H + with decreased bicarbonate
- increased H + production eg DKA
- decreased H + excretion eg RTA
- bicarbonate loss eg intestinal fistula
if compensated - low CO2
3 causes of respiratory acidosis
increased CO2 producing increased H+ and a slightly increased bicarb
- decreased ventilation
- poor lung perfusion
- impaired gas exchange
slower kidney compensation - increased H+ excretion and bicarb generation
3 causes of metabolic alkalosis
decreased H+ (increased pH) with increased bicarbonate
- H+ loss (pyloric stenosis)
- hypokalaemia
- ingestion of bicarbonate
rise in C02 to compensate
3 causes of respiratory alkalosis
due to hyperventilation
- voluntary
- artificial ventilation
- stimulation of respiratory centre
