Acid base Flashcards
How is CO2 transport linked with H+ production?
CO2 can bind to H2O to form HCO3-
CO2 can bind to proteins to form carbamino compounds.
Both of these reactions produce H+, so both impact pH.
How is H+ buffered in blood?
Plasma proteins - the amine group binds to H+ to form NH3+.
H+ binds to haemoglobin. Deoxyhaemoglobin is a stronger base, so better binds H+.
The CO2/HCO3- buffers, as equilibrium shifts can generate more or less H+.
What is the effectiveness of buffers?
A buffer is most effective when its pH is at its pKa.
pKa is 50% dissociation between ionised and unionised forms.
What is the effectiveness of the CO2/HCO3- buffer?
Its pKa is 6, and pH is at 7, so it is not chemically a good buffer it is effective because:
Relatively high concentrations
Metabolism adds more CO2 to the system
Both components of the system can be tightly regulated.
What is the CO2/HCO3- values in the Henderson Hasselbach equation?
pH = pKa + log [HCO3-]/0.34 x [PaCO2]
= 6.1 + log 21 / 0.23x5.2
= 6.1 + log 20
6.1 + 1.3 = 7.4 pH
What are the ratios of the CO2/HCO3- buffer?
For normal pH, the ratio before log is 20.
Ratio more than 20 will increase pH - alkalosis.
Ratio less than 20 will decrease pH - acidosis.
How is pH regulated?
pH = pKa + log [kidney/lungs]
CO2 is regulated by the lungs.
HCO3- is regulated by the kidneys.
These can be controlled independently.
The lungs remove more CO2 than the kidneys, so are more important in controlling pH.
What are the types of acidosis and alkalosis?
Respiratory - the cause of the change in pH is due to a change in PCO2.
Metabolic - the cause of the change in pH is due to a change in HCO3-.
What is compensation?
A disturbance is compensated by the other system - the pH is returned towards normal.
Respiratory disturbances are compensated by the kidneys.
Metabolic disturbances are compensated by the lungs.
The condition is only corrected when the correct pH and ratio is achieved.
What is the Davenport diagram?
See picture.
What are the values of the Davenport diagram?
Healthy HCO3- is 24mM.
Healthy pH is 7.4.
The blue line is the buffer line - controlled by haemoglobin levels.
The green lines are PCO2 values, controlled by respiratory movement.
Can only move in one direction at a time.
See picture.
What is respiratory acidosis?
Increased CO2
Often caused by impaired gas exchange.
H2O + CO2 <–> H2CO3 <–> H2CO3 <–> H+ + HCO3-
The equilibrium is shifted right, which produces more H+, decreases pH, and increases HCO3-.
What is the metabolic compensation for respiratory acidosis?
More HCO3- is filtered by the kidney, so more HCO3- is reabsorbed.
H+ is excreted and pH increases to restore pH to normal.
HCO3- is raised further.
What does the Davenport diagram look like for respiratory acidosis?
See picture.
There is first an upwards respiratory acidosis, which increased HCO3-.
The next movement is metabolic compensation, which generates more HCO3- to remove H+, and moves equilibrium left to increase pH.
What is respiratory alkalosis?
Decreased CO2.
Often due to hypoxia stimulating breathing.
H2O + CO2 <–> H2CO3 <–> H+ + HCO3-
Equilibrium pushed left, so less H+ and higher pH, and lowered HCO3-.
What is the compensation for respiratory alkalosis?
Less HCO3- is filtered by the kidneys, so less is reabsorbed, and less H+ is secreted.
H+ is retained, which lowers pH towards normal, and HCO3- is lowered further.
What does the Davenport diagram look like for respiratory alkalosis?
See picture.
First respiratory alkalosis, which reduces HCO3- and increases pH.
Then there is metabolic compensation, which reduces HCO3- further to retain H+ and increase pH.
What is metabolic alkalosis?
Decreased H+ (not from CO2).
Caused by addition of base, like OH- which accepts H+ to form H2O.
H2O + CO2 <–> H2CO3 <–> H+ + HCO3-
Equilibrium is pushed to right as removing H+, which increases pH, and increases HCO3-.
What is the respiratory compensation for metabolic alkalosis?
The high pH will reduce peripheral chemoreceptor activity causing ventilation to decrease.
The decreased ventilation will cause in rise in PaCO2, pushing equilibrium right.
This increases H+ and so increases HCO3- further.
What does the Davenport diagram look like for metabolic alkalosis?
See picture.
First there is metabolic alkalosis, by removed H+ which increases HCO3-, and increases pH.
Then there is respiratory compensation, which increases CO2, so generates more H+ and decreases pH.
What is metabolic acidosis?
Increased H+ (not derived from CO2).
Caused by ingestion of acids or loss of HCO3-.
H2O + CO2 <–> H2CO3 <–> H+ + HCO3-
Equilibrium is pushed left resulting in low pH and reduced HCO3-.
What is the respiratory compensation for metabolic acidosis?
The low pH will stimulate peripheral chemoreceptors causing ventilation increase.
The increased ventilation will cause a fall in PCO2, pushing equilibrium further to the left, reducing HCO3- even more.
What is the Davenport diagram for metabolic acidosis?
See picture.
First metabolic acidosis reduces HCO3- and increases H+ which decreases pH
Then respiratory compensation reduces HCO3- further, and reduces H+ which increases pH.
