Acid-Base Balance Flashcards
Blood buffering system equation
CO2 + H2O = HCO3- + H+
What is the purpose of the Henderson-Hasselbalch equation?
Relates the pH to the ratio between the concentration of bicarbonate and the partial pressure of CO2
What does the Henderson-Hasselbalch equation show?
blood pH is driven by the ratio between bicarbonate production and partial pressure of CO2
What would the effect on blood pH be if bicarbonate levels increase?
increase
What would the effect on blood pH be if partial pressure of CO2 increases?
decrease
What is the usual range of pH?
7.35-7.45
When does respiratory acidosis occur?
Increase in blood CO2 due to respiratory system disorder
Causes of respiratory acidosis
- respiratory depression by opiates
- disorders of the respiratory muscles (e.g. polio)
- airway obstructions (e.g. sleep apnoea)
How does the body counteract respiratory acidosis?
Kidneys excrete more H+ and increase bicarbonate reabsorption
What are the causes for respiratory alkalosis?
Hyperventilation due to:
- hypoxaemia from high altitude
- pulmonary embolism
How does the body counteract respiratory alkalosis?
Kidney reabsorbs H+ ions
How does the urinary system alter blood pH?
- excretion of H+
- production and reabsorption of HCO3-
How are H+ ions excreted?
In the form of:
- dihydrogen phosphate (H2PO4-)
- ammonium (NH4+)
Explain the mechanism of H+ ions in the form of dihydrogen phosphate
- H+ ions actively transported into lumen via hydrogen-ATPase pumps
- Excess luminal phosphate can bind a large portion of H+
- This buffers them as H2PO4- before excretion
Explain the mechanism of excretion of H+ ions in the form of ammonium
- Glutamine -> glutamate + ammonium (PCT)
- Ammonium dissociates -> ammonia + H+
- Ammonia enters lumen (as it can pass membrane)
- Ammonia -> ammonium (by picking up luminal H+)
- Allows hydrogen to be excreted as ammonium ions
What can ammonia secreted at the PCT be used for?
Buffer and secrete H+ in the collecting duct
What can the glutamate created from glutamine be used for?
Forming bicarbonate
Where can bicarbonate ions be reabsorbed?
proximal convoluted tubule
Explain the mechanism of bicarbonate reabsorption
- H+ secreted into lumen to combine with filtered bicarbonate -> carbonic acid
- Carbonic acid -> CO2 + H2O
- Inside the cell, carbonic anhydrase converts CO2 + H2O -> carbonic acid
- Carbonic acid -> H+ + HCO3-
- HCO3- transported into blood
- H+ transported into lumen to repeat cycle
Explain the mechanism of bicarbonate production
- Metabolic activity of cells produces large amounts of CO2
- CO2 + H2O -> HCO3- + H+
- HCO3- enters the plasma
- H+ transported into lumen to drive HCO3- reabsorption
What other substrate can produce bicarbonate, and what is the byproduct?
amino acids
ammonium ions
What is the anion gap?
Way of determining the cause of a metabolic acidosis
What is the anion gap formula?
(Na+ + K+) - (Cl- + HCO3-)
When does metabolic acidosis occur?
pH blood < 7.35
What are the general causes of metabolic acidosis?
- increase in H+, lactate and organic acids
- loss of HCO3-
What are the symptoms of metabolic acidosis?
- hyperventilation
- confusion
- tachycardia
How would you diagnose metabolic acidosis/alkalosis?
arterial blood gas analysis
When does metabolic alkalosis occur?
pH blood > 7.45
What are the general causes of metabolic alkalosis?
- massive loss of H+
- increase of HCO3-
What are the symptoms of metabolic alkalosis?
- hypoventilation
- confusion
- tetany
- tremor
