Physiology 8: Acid Base Balance Flashcards
A person is of normal acid base balance if
- plasma pH is around 7.4 (range from 7.35 to 7.45)
- HCO3- close to 25 mol/litre (range from 23-37mmol/litre)
- arterial PCO2 close to 40mmHg (range from 35-45)
if normal acid base balance is disturbed the first and number one priority is to
restore pH to 7.4 as soon as possible which is known as compensation for an acid base disturbance
Therefore, compensation is said to be
the restoration of pH irrespective of what happens to bicarbonate and PCO2
correction on the other hand
is the restoration of pH, HCO3- and PCO2 to normal
classification of disturbances to acid base balance
- respiratory in origin
- non-reparatory in origin
respiratory in origin
- Respiratory acidosis= plasma pH falls
2. Respiratory alkalosis= plasma pH rises
non-respiratory origin
- Metabolic acidosis= plasma pH falls
2. Metabolic alkalosis= plasma pH rises
immediate buffering of a chance in pH
- immediate dilution of acid or base present in the exta-cellualr fluid
- Blood buffers are Hb and HCO3- IE in acidosis where there are excess hydrogen ions in the blood bicarbonate buffers them
- this is a very rapid response however, buffers quickly get depleted and the kidney has to replenish stores
blood gas analysis can measure
pH and PCO2 and bicarbonate can be calculated
kidneys regulate
bicarbonate concentration in the blood
lungs regulate
the partial pressure of CO2 in the blood
respiratory acidosis caused by
retention of CO2 by the body which is caused by HYPOventilation
causes of respiratory acidosis
- COPD
- respiratory restriction
- respiratory depression caused by opitate compounds and general anaesthetics
so how do theses respiratory problems generate an acidosis
the excess carbon dioxide in the blood shifts the equilibrium to the right
H20 + CO2 H2CO3- H+ AND HCO3-
- This causes an increase in both the hydrogen and bicarbonate ion concentration, the H+ ions cause the acidosis and you might think the increase in bicarbonate ions should compensate HOWEVER, A BUFFER SYSTEM CANNOT BUFFER ITSELF
Uncompensated respiratory acidosis
LOW PH HIGH PCO2
Compensation for respiratory acidosis
- There is no extra-cellular buffering because a buffer cannot buffer itself, since the respiratory system is the cause the renal system must compensate: REMEMBER BLOOD CO2 CONCENTRATION DRIVES TUBULAR HYDROGEN ION SECRETION, therefore, the more CO2 retained the more H+ ions secreted into the filtrate
renal compensation for respiratory acidosis is as follows
- H+ tubular secretion
- All filtered bicarbonate ions are re-absorbed
- H+ is continually secreted and generates a titratable acid and ammonium
- acid is excreted and new bicarbonate ions are added to the blood, therefore bicarbonate ion concentration increases as a result of the underlying disorder and because bicarbonate is added to the blood
CORRECTION OF RESPIRATORY ACIDOSIS
requires lowering PCO2 by restoring normal ventilation
respiratory alkalosis problem
excessive loss of CO2 from the body caused by hyperventilation
causes of respiratory alkalosis
- low inspired PO2 at high altitudes (which stimulates the peripheral chemoreceptors to cause hyperventilation), panic attacks, brainstem damage
how do these repsiraoty problems cause an alkalosis
- they cause the equilibrium to shift to the left
CO2+ H20 H2C03- HCO3- AND H+ - the shift in equilibrium reduction in bicarbonate and hydrogen ions
- the reduction in hydrogen ions causes the alkalosis
decompensated respiratory alkalosis
HIGH PH LOW PCO2
Renal compensation for respiratory alkalosis
- since the respiratory system is the problem then the renal system has to compensate
- remember blood PCO2 drives hydrogen ion secretion into the tubules, so the less PCO2 in the blood the less hydrogen ions being secreted into the tubules
therefore, compensation for respiratory alkalosis is as follows
- reduction in hydrogen ion secretion into the tubules because there is reduced PCO2 concentration in the blood
- there is reduced bicarbonate re-absorption in the tubules even though the shift in equilibrium has reduced the amount if bicarbonate filtered therefore, bicarbonate gets excreted causing the urine to be ALKALINE
- no titratable acid or ammonium are formed therefore, BICARBONATE IONS ARE NOT ADDED TO THE BLOOD
- so renal compensation for the respiratory alkalosis actually further lowers the bicarbonate
