Alveoli Picture

The alveoli are the final branching of the respiratory
tree and act as the primary gas exchange units of the lung. The gas-blood
barrier between the alveolar space and the pulmonary capillaries is
extremely thin, allowing for rapid gas exchange. To reach the blood, oxygen
must diffuse through the alveolar epithelium, a thin interstitial space, and
the capillary endothelium; CO2 follows the reverse course to reach the
alveoli

Picture of Alveoli ruptured as a result of emphysema

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