Sat27November0445PM 24

A buffer is a solution consisting of a weak acid and its conjugate base. This is able to resist a change in pH when a stronger acid or base is added.

Which is the single most effective buffer in blood?

(Please select 1 option)

Haemoglobin

Bicarbonate This is the correct answer

Plasma protein Incorrect answer selected

Organic phosphates

Inorganic phosphates

Explanation

The bicarbonate ion (HCO3-) contributes most to the buffering capacity of whole blood.

Bicarbonate within the red blood cell contributes approximately 18% of total buffering capacity and that dissolved in plasma contributes 35% (total 53%).

When a strong acid is added to the bicarbonate buffer, the hydrogen ions released from the acid combine with the HCO3- to form carbonic acid (H2CO3). This then dissociates to H2O and CO2 under the influence of the enzyme carbonic anhydrase.

Buffering capacity of whole blood:

Red blood cells:

Haemoglobin 35%

Bicarbonate 18%

Organic phosphates 3%

Plasma:

Bicarbonate 35%

Plasma protein 7%

Inorganic phosphate 2%

Answer Statistics

1

29%

2

56%

3

15%

4

2%

5

2%

Times answered: 250