Physiology 6 - Acid Base Balance Flashcards
What is the normal pH range of blood?
7.35 - 7.45
Why is venous blood more acidic than arterial blood?
It contains more CO2
What effect does acidosis have on the nervous system?
CNS depression
What effect does alkalosis have on the nervous system?
Hyperactivity of the PNS, and eventually CNS
What effect does acidosis have on potassium concentrations?
Hyperkalaemia
What is formed in the middle step of the buffer system for acid base balance in the body?
Carbonic acid
The formation of carbonic acid from carbon dioxide and water is catalysed by what enzyme?
Carbonic anhydrase
The concentration of plasma bicarbonate is controlled by what body system?
Renal
The partial pressure of carbon dioxide is controlled by what body system?
Respiratory
Reabsorption of bicarbonate in the tubules of the nephron is driven by what?
Secretion of hydrogen ions
When bicarbonate concentrations in tubular fluid are low due to reabsorption, what do secreted hydrogen ions combine with instead?
Phosphate
In individuals with severe acidosis, excess hydrogen ions can combine with what to be excreted in the urine?
Ammonia
Death occurs if the pH of blood drops below what value?
6.8
Death occurs if the pH of blood rises above what value?
8
What is the average plasma HCO3- concentration?
25mmol/l
What is the average partial pressure of arterial CO2?
40mmHg
What is meant by compensation of an acid base balance?
Restoration of the pH, irrespective of what happens to bicarbonate and carbon dioxide
What is meant by correction of an acid base balance?
Restoration of the pH, bicarbonate and carbon dioxide
What acid base balance disruption occurs when carbon is retained by the body?
Respiratory acidosis
Clinically, what is the cause of respiratory acidosis?
Type 2 respiratory failure
What happens to pH and partial pressure of carbon dioxide in uncompensated respiratory acidosis?
pH is low, partial pressure of carbon dioxide is high
How is respiratory acidosis compensated for?
Reabsorption of bicarbonate and formation of ‘new’ bicarbonate
What acid base balance disruption occurs when there is excess removal of carbon dioxide by the body?
Respiratory alkalosis
Clinically, what is the cause of respiratory alkalosis?
Hyperventilation
What happens to pH and partial pressure of carbon dioxide in uncompensated respiratory alkalosis?
pH is high, partial pressure of carbon dioxide is low
How is respiratory alkalosis compensated for?
Excretion of bicarbonate in urine
What is the most common acid base disturbance?
Metabolic acidosis
What acid base balance disruption occurs when there is excess hydrogen ions in the blood, from a source which is not carbon dioxide?
Metabolic acidosis
What happens to pH and bicarbonate concentration in uncompensated metabolic acidosis?
pH is low, bicarbonate concentration is low
How is metabolic acidosis compensated for?
Increased ventilation
What acid base balance disruption occurs when there is excessive loss of hydrogen ions from the body, from a source which is not carbon dioxide?
Metabolic alkalosis
What happens to pH and bicarbonate concentration in uncompensated metabolic alkalosis?
pH is high, bicarbonate concentration is high
How is metabolic alkalosis compensated for?
Decreased ventilation
Which acid base disturbance often occurs in pregnancy?
Respiratory alkalosis
Which acid base disturbance can be caused by burns?
Metabolic alkalosis
Which acid base disturbance can be caused by diarrhoea?
Metabolic acidosis
Which acid base disturbance can be caused by vomiting?
Metabolic alkalosis
Which acid base disturbance can be caused by diuretic use?
Metabolic alkalosis
Which acid base disturbance can be caused by a PE?
Respiratory alkalosis
In which acid-base disorder is the anion gap of significance?
Metabolic acidosis
What does the anion gap estimate?
Unmeasured plasma ions (e.g. phosphate, ketones, lactate)
How is the anion gap calculated?
(Sodium + potassium) - (chloride + bicarbonate)
What is the normal anion gap?
10 - 18mmol/l
Metabolic acidosis with a normal anion gap can be due to what two things?
Loss of bicarbonate or ingestion of H+ ions
Metabolic acidosis with a raised anion gap is due to what?
Increased production or reduced excretion of organic acids
What is the anion gap in metabolic acidosis caused by renal tubular acidosis?
Normal
What is the anion gap in metabolic acidosis caused by diarrhoea?
Normal
What is the anion gap in metabolic acidosis caused by Addison’s disease?
Normal
What is the anion gap in metabolic acidosis caused by shock, infection or tissue ischaemia?
Raised (raised lactate)
What is the anion gap in metabolic acidosis caused by renal failure?
Raised (raised urate)
What is the anion gap in metabolic acidosis caused by DKA?
Raised (raised ketones)
Hypokalaemia is associated with which acid-base disorder?
Metabolic alkalosis
Hyperkalaemia is associated with which acid-base disorder?
Metabolic acidosis
What will the PaO2 usually be in patients with respiratory acidosis?
Low
