5.3.1. Acid/Base Balance - Buffers - The Bicarbonate Buffer System Flashcards
What is the purpose of buffers?
To minimize the change in pH when H+ ions are added/removed.
What is the most important extracellular buffer system?
The bicarbonate buffer system
What are bicarbonate and H+ ions in equilibrium with?
Carbonic Acid (H2CO3)
What is the method (using equations) to show the ratio of bicarbonate ions to Carbonic Acid in the blood?
H2CO3 is in equilibrium with (H+) + (HCO3-)
pH = pK + log([HCO3-] / [H2CO3])
7.4 = 6.1 + log([HCO3-] / [H2CO3])
1.3 = log([HCO3-] / [H2CO3])
1.3 = log 20
Therefore: [HCO3-] / [H2CO3] = 20
Therefore there is 20 x more bicarbonate than carbonic acid at the normal pH of 7.4
What does the concentration of the weak acid (Carbonic Acid / H2CO3) depend on?
The amount of CO2 dissolved in the plasma
What does the amount of CO2 dissolved in the plasma depend on?
- The solubility of CO2
2. The PCO2
What us the solubility of CO2 in the blood at 37 degrees?
0.03mmol / mmHg PCO2
What is the normal PCO2?
40mmHg
So what is the normal concentration of Carbonic Acid (H2CO3), at 37 degrees?
CO2 Solubility = 0.03mmol / mmHg PCO2
PCO2 = 40mmHg
Concentration of Carbonic Acid = 0.03 x 40mmol/L
= 1.2mmol/L
Since the ratio (at normal) of the bicarbonate to carbonic acid is 20:1, and the normal concentration of carbonic acid is 1.2mmo/L, what is the concentration of bicarbonate (at normal)?
20 x 1.2mmol/L
= 24mmol/L
What is a simplified version of the equation relating pH to bicarbonate and PCO2?
pH is directly proportional to [HCO3-] / PCO2
Why is the relationship between pH, bicarbonate and PCO2 important?
As this effects the basic mechanism by which bicarbonate acts as a buffer
What happens if there is an increase in Extracellular H+ ion concentration?
H+ + HCO3- = H2CO3 = H2O + CO2
Note = is meant to be the equilibrium sign, but it does not appear on this website
This would push the above equation to the right, and the CO2 will be exhaled (removed from the system)
