Physiology - Acid-Base Balance II: Whole Body Acid-Base Balance Flashcards
How can a normal acid-base blanace be described in terms of metabolic components?
Plasma pH - 7.35-7.45
Bicarbonate - 25mmol/l
Arterial PCO2 - 40mmHg
What is the difference between compensation and correction in terms of acid-base balance?
First priority is to restore pH to 7.4 as soon as possible
Compensation is the restoration of pH irrespective of what happens to [HCO3-]p and PCO2
Correction of an A-B disturbance is restoration of pH and [HCO3-]p and PCO2 to normal
What is the first “line of defence” against pH changes in the blood?
Blood buffers
What is the role of the renal system in terms of mainatining buffer solutions?
As buffer stores become depleted, the kidney will reabsorb and rectify stores
From the Henderson-Hasselbalch equation, pH is shown to be in direct proportion to what?
pH is in direct propertion to [HCO3-]/[CO2]
(this is the Henderson Hasselbach equation)
In basic terms, what cause respiratory acidosis?
Retention of CO2 by the body
(e.g. emphysema)
Why does CO2 retention in respiratory acidosis result in an acidosis?
Increased CO2 drives the equilibrium to the right producing more hydrogen ions and bicarbonate
(acidosis occurs since the buffer cannot buffer itself e.g. Hydrogen ions cannot be buffered by bicarbonate - stong acids completely dissociate in solution)
How can an uncompensated respiratory acidosis be defined?
pH < 7.35 and PCO2 > 45 mmHg
How do the kidneys compensate for a respiratory acidosis?
Blood PCO2 drives H+ secretion by the kidney
Therefore, CO2 retention stimulates H+ secretion into the filtrate (generates titratable acid and ammonium ions)
Bicarbonate is also retained and new bicarbonate is added
Correct of a respiratory acidosis requires what?
Restoration of ventilatory function of the lungs
How does respiratory alkalosis come about?
Excess removal of CO2 from the blood
(e.g. low inspired PO2 at high altitude, causes hyperventilation which lowers PCO2)
How does a respiratory alkalosis come about?
Excess CO2 removal from the blood
Drive equilibrium to the left
Reduces bicarbonate concentration in the blood
How is a respiratory alkalosis compensated for?
Hydrogen ion secretion is reduced
Bicarbonate is excreted in the urine
No titratable acid and ammonia is produced so less new bicarbonate is generated
How is respiratory alkalosis corrected in full?
Resoration of normal ventilation
How is a metabolic acidosis defined?
Excess H+ from any source other than CO2
(e.g. ingestion of acid, lactic acidosis after exercise, DKA, excessive loss of base e.g diarrhoea)
In someone suffering from metabolic acidosis, there is a _________ level of bicarconate ions in the blood
In someone suffering from metabolic acidosis, there is a reduced level of bicarconate ions in the blood
How is a metabolic acidosis compensated for?
Peripheral chemoreceptors are stimuated as pH lowers
Buffer reaction shifts to the left
CO2 in the blood is increased
Ventilation increases to blow off excess CO2
How is a metabolic acidosis corrected?
Renal system
Bicarbonate ions are reabsorbed easily (as they are in low concentartion)
Titratable acid and ammonium ions are produced in tubular fluid and excreted in urine
New bicarbonate ions are created by this process
Ventilation can then normalise
In a metabolic acidosis, why is respiratory compensation required?
Acid load cannot be excreted immediately so needs respiratory compensation until this can occur
How is metabolic alkalosis defined?
Excessve acid loss from the body
(e.g. vomiting, ingestion of alkali, aldosterone hypersecretion)
How does the respiratory system compensate for a metabolic alkalosis?
CO2 is retianed as breathing slows
The buffer equation shifts to the right
Hydrogen ions increase
How is metabolic alkalosis corrected?
Some bicarbonate is not reabsorbed and lost in the urine
No titratable acid or ammonium ions are created and secreted
Less new bicarbonate is produced
In respiratory acidosis, there is a ________ acid concentration and a _________ bicarbonate concentration
In respiratory acidosis, there is a high acid concentration and a low bicarbonate concentration
In metabolic acidosis, there is a ________ acid concentration and a _________ bicarbonate concentration
In metabolic acidosis, there is a high acid concentration and a high bicarbonate concentration
In metabolic alkalosis, there is a ________ acid concentration and a _________ bicarbonate concentration
In metabolic alkalosis, there is a low acid concentration and a high bicarbonate concentration
In respiratory alkalosis, there is a ________ acid concentration and a _________ bicarbonate concentration
In respiratory alkalosis, there is a low acid concentration and a low bicarbonate concentration
