acid base balance Flashcards
what is an acid?
proton donator
what is a base?
proton acceptor
what is pH?
-log10[H+]
what does a lower pH mean?
acidic
what does a higher pH mean?
alkali
what is the ECF pH range?
7.35-7.45
what is acidosis?
when pH falls below 7.35
what is alkalosis?
when pH rises above 7.45
what are metabolic sources of H+?
carbohydrates - carbonic and lactic acid
proteins - sulfuric acid
fats - acidic ketone bodies
DNA - sulfuric acid
what are the systems in place to regulate H+ levels?
chemical buffers
acid excretion: renal or respiration
what is a buffer?
a solution that is resistant to small changes in pH
what does an acidic buffer contain?
weak acid and conjugate base
what does a basic buffer contain?
weak base and its conjugate acid
what buffers are in the body?
phospate
protein
bicarbonate
haemoglobin
what is the phosphate buffer equation?
H+ + HPO4^2- –> H2PO4^2-
explain how protein buffers work?
if pH falls (too acidic) - amine group of protein acts as a base and accepts a proton (NH3+)
if pH rises (to alkali) - carboxyl group acts as an acid and donates a H+
why does the protein buffer system have such a large effect?
bc there are so many proteins
what sources can bicarbonate buffer system buffer H+ from?
any source other than CO2
put the buffers of the body in order of highest to lowest buffer capacity
bicarbonate - majority
haemoglobin
protein
phosphate - least bc its in the kidneys
what is the equation for the haemoglobin buffer system?
Hb + H+ –> HHb
what is HHb?
deoxyhaemoglobin
why is the haemogloin buffer system helpful?
bc Hb is actively pumped around the body
what is the normal range of CO2 in the blood?
35-45mmHg = 4.7-6.0kPa
how do the lungs help in acid-base balance?
eliminating or retaining CO2 by changing the rate or depth of respirations
why are the lungs quick at changing acid base balance? what limits this?
quick bc the brain can change respiratory rate quickly
limited by the amount of CO2 expired at one time
how do the kidneys maintain acid-base balance?
by excreting or conserving bicarbonate and hydrogen ions
what is the henderson hasselbach equation?
acidity is inversely proportional to bicarbonate/carbon dioxide
what do you diagnose an acid base disorder?
clinical history
targeted physical exam
ABG
what is the mechanism of respiratory acidosis?
hypoventilation - more CO2 retained
or more CO2 produced
what are the causes of respiratory acidosis?
COPD neuromuscular disorder respiratory centre depression Late acute respiratory distress syndrome inadequate mechanical ventilation sepsis/burns
how will respiratory acidosis present?
- CO2 retained, pCO2 is high
- low pH
what is the compensatory mechanism of respiratory acidosis?
renal
less HCO3- produced (more resorbed)
some respiratory compensation –> increased ventilation rate
what is the mechanism of respiratory alkalosis?
hyperventilation
what are the causes of respiratory alkalosis?
anxiety, stress or pain elevated body temp overventilation with ventilator CNS trauma or tumour Hypoxemia
how will respiratory alkalosis present?
pH rises
pCO2 falls
what is the compensation mechanism of respiratory alkalosis?
renal
HCO3- secreted (less reabsorbed)
what is the mechanism of metabolic acidosis?
Increased H+ –> more acid production or retention
Bicarbonate loss
what are the causes of metabolic acidosis?
conditions that increase blood acids - renal failure, diabetic ketoacidosis, starvation and lactic acidosis
chronic diarrhoea
toxins
carbonic anhydrase inhibitors
how will metabolic acidosis present?
low pH
bicarbonate falls
decreased CO2
how is metabolic acidosis corrected?
hyperventilation
CO2 decreased
what is the mechanism of metabolic alkalosis?
HCO3- is elevated bc carbohydrate retention or loss of acid
what causes metabolic alkalosis?
- acid loss due to vomiting or gastric suction
- loss of potassium due to steroids or diuresis
- overuse of antacids
how does metabolic alkalosis present?
high pH
high HCO3-
how is metabolic alkalosis corrected?
pCO2 increased
hypoventilation
what is the normal anion gap?
8-12 mmol/L
how is the anion gap calculated?
([K+}+{Na+)] - ([Cl-}+{HCO3-}]
what does a high anion gap indicate?
loss of HCO3- without concurrent increase of Cl-
