Read the CO2 Journey from Tissue to Alveolus
Blood carries most carbon dioxide after converting it reversibly to bicarbonate in red blood cells.
Carbon Dioxide Transport is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
At tissues
CO2 enters red cells; carbonic anhydrase speeds its hydration to carbonic acid, which dissociates to H+ and bicarbonate. Bicarbonate moves into plasma as chloride enters (Hamburger/chloride shift). Some CO2 dissolves; some binds globin amino groups as carbaminohaemoglobin.
At lungs
The process reverses: bicarbonate re-enters red cells as chloride exits. Carbonic anhydrase supports CO2 regeneration, and CO2 diffuses into alveoli for exhalation.
OlympIQ exam lens
- ✓Most CO2 travels as plasma bicarbonate.
- ✓Carbamino binding is to globin, not haem iron.
- ✓Tissues: bicarbonate out, chloride in; lungs: reverse.
The chloride shift reverses direction between tissues and lungs.
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