6.4. Simple Acid/Base Disorders - Metabolic Acidosis Flashcards
What is metabolic acidosis?
Acidosis of metabolic origin
What is the mechanism of metabolic acidosis?
A reduction in blood bicarbonate
What can cause a reduction in blood bicarbonate?
- An increase buffering of H+ ions
2. Direct loss of bicarbonate
What must happen to the PCO2 in metabolic acidosis, to protect the pH?
The PCO2 must be decreased
What can cause metabolic acidosis?
- Increase in H+ ion production, as in lactic-acidosis / ketoacidosis (of a diabetic)
- Failure to excrete the normal dietary load of H+ ions, as in renal failure
- Loss of bicarbonate ions, as in diarrhoea (i.e. failure to absorb intestinal bicarbonate)
What does the resulting acidosis stimulate?
Increased ventilation (Depth not Speed) so that the PCO2 can fall
What normally correct the pH disturbance?
The kidneys
How do the kidneys normally correct the pH disturbance?
- By restoring the blood bicarbonate concentration
2. By excreting H+ ions
Why can the kidneys not correct the pH disturbance?
Due to the source of the H+ ions, is the carbonic acid from the CO2, and these are secreted into the tubule lumen
- In what direction is the response to Acid/Base disturbances?
- Why?
- The same direction
2. Due to it being the ratio between the [HCO3-] and PCO2
Why is complete compensation never reached?
As this would remove the drive to correct the original disturbance
What happens as a result of the decrease in PCO2 (as a a corrective mechanism)?
The total amount of H+ secreted by the renal tubule is less than normal due:
- A large decrease in the HCO3- reabsorption
- An increase in the HCO3- generation
What does an increase in metabolic H+ ions cause within the body?
- Immediate buffering in the ECF
- Buffering in the ICF
- Respiratory compensation within minutes - which will decrease when the bicarbonate levels rise
- Renal correction of the disturbance - this takes longer to develop the full response as renal glutaminase takes 4-5 days to reach its maximum
