Page 13, Later Development, Develop. Physiol., Dr. D. Penney

Carbon Dioxide Transport:

There are three mechanisms by which CO2 is carried in the blood (Figure 3.06). Some CO2 dissolves in the water of the plasma and remains in that form.

Most of the CO2, however, diffuses into the erythrocyte and reacts with water molecules in the presence of the enzyme catalase, forming carbonic acid. This weak acid dissociates into H+ and bicarbonate ion. The bicarbonate leaves the red cell and stays in the plasma. To maintain a constant electrical charge in the red cell, chloride ion diffuses into the red cell.

Another small fraction of the CO2 binds to hemoglobin, forming a carbamino compound. Carbon dioxide carriage by the blood is affected by the extent of hemoglobin saturation with oxygen. As percent saturation rises, the percent hemoglobin saturation with CO2 falls at any given PCO2. This is known as the Christianson-Douglas-Haldane effect.

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