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How does blood remove carbon dioxide from body tissues?
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blood
Blood sediment in test tubes, showing plasma (clear fluid), red blood cells (red), and the release of hemoglobin into the surrounding plasma (pink).
Blood removes carbon dioxide from body tissues primarily through diffusion, driven by the higher partial pressure of carbon dioxide in the tissues compared to the blood. Once in the blood, carbon dioxide is transported to the lungs via three main mechanisms:12
- Bicarbonate Ions: About 88 percent of carbon dioxide is converted into bicarbonate. Inside red blood cells, the enzyme carbonic anhydrase rapidly catalyzes the reaction of carbon dioxide with water to form carbonic acid, which then dissociates into hydrogen and bicarbonate ions. Through the chloride shift, bicarbonate is moved into the plasma in exchange for chloride ions, allowing the plasma to serve as a storage site.134
- Carbamate: Some carbon dioxide binds directly to blood proteins, primarily hemoglobin, to form carbamate. This process is enhanced when hemoglobin releases oxygen in the tissues.1
- Dissolved Gas: A small portion, approximately 5 percent, remains dissolved in the blood without chemical change.1
These processes ensure that carbon dioxide is efficiently carried to the lungs for elimination.15