Final answer:
Carbonic acid (H₂CO₃) dissociates into CO₂ and H₂O, enabling the lungs to eliminate carbon dioxide and maintain acid-base balance in the body through the action of carbonic anhydrase and the chloride shift.
Step-by-step explanation:
Carbonic acid (H₂CO₃) dissociates in the blood into carbon dioxide (CO₂) and water (H₂O), allowing carbon dioxide to be eliminated by the lungs. This process is crucial for maintaining the acid-base balance within the body. The key enzyme involved in this reaction is carbonic anhydrase (CA), which catalyzes the reversible reaction where CO₂ combines with H₂O to form H₂CO₃. H₂CO₃ then quickly dissociates into bicarbonate ions (HCO₃) and hydrogen ions (H+).
In the red blood cells, hemoglobin binds to the free H+ ions, limiting shifts in blood pH and facilitating the transport of bicarbonate out of the cell in exchange for chloride ions, in a process known as the chloride shift. Upon reaching the lungs, the bicarbonate ions are transported back into the red blood cells and recombine with H+ to form carbonic acid, which is then converted again into CO₂ and H₂O by carbonic anhydrase. The CO₂ diffuses into the alveoli and is then exhaled, effectively removing excess CO₂ from the bloodstream and helping to regulate the body's pH levels.