Buffer solutions in the body Flashcards
(10 cards)
What is a buffer solution?
A system that minimises pH changes on addition of small amounts an acid or a base.
What buffer is present in blood plasma? Maintains pH between?
The H2CO3/HCO3- buffer - maintains the pH buffer between 7.35 and 7.45.
What happens if our pH in blood plasma falls below 7.35?
People can develop acidosis - fatigue.
What happens if our pH in blood plasma rises above 7.45?
People can develop alkalosis - muscle spasms.
Why is the pH scale so sensitive?
Because a difference of just 0.30 pH units is a two-fold difference in H+ concentration.
What happens in the carbonic-hydrogenate buffer system when acid is added?
- [H+] increases.
- [H+] ions react with the conjugate base, HCO3-.
- The equilibrium position shifts to the left, removing most of the H+ ions.
H2CO3 = H+ + HCO3-
<—————————-
added acid
What happens in the carbonic-hydrogenate buffer system when alkali is added?
- [OH-] increases.
- The small concentration of H+ ions reacts with the OH- ions.
H+ + OH- = H2O. - H2CO3 dissociates, shifting the equilibrium position to the right to restore most of the H+ ions.
H2CO3 = H+ + HCO3-
—————————–>
added alkali
Calculate the concentration ratio of HCO3-/H2CO3 in healthy blood:
- The pKa for the carbonic acid-hydrogencarbonate equilibrium is 6.1 at body temperature.
- What is the ratio of HCO3-/H2CO3 in healthy blood at a pH of 7.40?
- Express HCO3-/H2CO3 in terms of Ka and H+:
H2CO3 = H+ + HCO3-
Ka = ([H+] x [HCO3-]) / [H2CO3]
[HCO3-] = Ka
[H2CO3] [H+]
- Convert pH into [H+] and pKa into Ka.
[H+] = 10^-7.40 = 3.98 x 10^-8 moldm-3.
Ka = 10^-pKa = 10^-7.40 = 3.98 x 10^-8 moldm-3.
- Calculate the HCO3-/H2CO3 ratio:
[HCO3-]/ = Ka/ = 7.9 x 10^-7/
[H2CO3] [H+] = 3.98 x 10^-8
= 20/1.
How does the body prevent H2CO3 build up?
By converting it into CO2 (g), which is then exhaled by the lungs.
What is the carbonic-acid hydrogencarbonate ion equilibrium?
added alkali
—————————->
H2CO3 = H+ + HCO3-
<—————————-
added acid
