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How do the lungs change the oxygen and carbon dioxide content of blood?
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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).
In the lungs, the blood undergoes a vital transformation through the process of gas exchange, which converts oxygen-poor venous blood into oxygen-rich arterial blood. This exchange occurs via diffusion across the thin, immense surface area of the alveoli and the surrounding pulmonary capillaries.123
Mechanisms of Exchange
- Oxygenation: Oxygen moves from the inhaled air in the alveoli into the blood, where it binds primarily to hemoglobin within red blood cells. This process is driven by the higher partial pressure of oxygen in the alveoli compared to the blood.24
- Carbon Dioxide Removal: Carbon dioxide, which is transported in the blood as bicarbonate, carbamate, and in solution, diffuses from the blood into the alveoli to be exhaled. The oxygenation of hemoglobin in the lungs triggers a structural change that facilitates the release and elimination of carbon dioxide.51
This efficient matching of ventilation and blood flow ensures that the body maintains the necessary gas concentrations to support metabolism.26