Question

The pH of the blood is maintained by balancing the ratio of

• A. Lactic acid and pyruvic acid
• B. NaHCO${}_3$ and H${}_2$CO${}_3$
• C. Pyruvic acid and H${}_2$CO${}_3$
• D. None of the above

Answer 1

The correct option is B NaHCO${}_3$ and H${}_2$CO${}_3$

There is bicarbonate buffering system, which is an important buffer system in the acid-base homeostasis.
In this system, carbon dioxide, CO${}_2$, combines with water (H${}_2$O) to form carbonic acid (H${}_2$CO${}_3$), which in turn rapidly dissociates to form hydrogen ion, H${}^{+}$ and bicarbonate ion, HCO${}_3$ as:
CO${}_2$ + H${}_2$O --> H${}_2$CO${}_3$ --> HCO${}_3$${}^{-}$ + H${}^{+}$
This reaction is reversible and is catalyzed by the enzyme carbonic anhydrase.
The most important constituents of blood that keep the pH value within the limits of 6.8 - 7.8 are formed by the sodium bicarbonate (NaHCO${}_3$) and carbonic acid (H${}_2$CO${}_3$). When the proportion of carbonic acid increases, the blood will become acidic. If that happens, one automatically starts to breathe more deeply to get rid of more carbon dioxide through the lungs and to become less acidic. When acidification continues the alkaline buffer, formed by sodium bicarbonate, ensures that the acid in the blood is neutralized.
Thus, the correct answer is option B.