Smoker's Lung: Pathology Photo Essay (cont.)
What processes determine normal function of the lung?
As just indicated, the main function of the lung is the exchange of the gases
oxygen and carbon dioxide. So, the blood in the alveolar capillaries takes
oxygen from inhaled air that is in the alveoli. Then, the oxygenated blood
circulates through the body to deliver the oxygen to the tissues. In the
exchange of gases, the blood in the alveolar capillaries releases carbon dioxide
to the alveoli. Then, when we breathe out (exhale or expire), the carbon dioxide
is removed from the alveoli through the airway and eliminated from body.
Accordingly, three processes determine normal lung function:
- Ventilation
- Diffusion
- Blood supply
Ventilation is the moving of air into and out of the lung. This process
requires an open (unobstructed) airway. Increasing and decreasing the size of
the chest cavity is what accomplishes the movement of air. You see, as the chest
cavity enlarges, a vacuum is created in the airway and air rushes in. Then, with
breathing out, the chest cavity becomes smaller and air is pushed out. The
muscles in the chest wall (intercostal muscles between the ribs), and the muscles
in the diaphragm work together to change the size of the chest cavity. (The
diaphragm is a flat muscular membrane that separates the chest from the
abdomen.) In addition, when we breathe really hard, we even use muscles in the
neck (referred to as accessory muscles for breathing) to help expand the chest.
Diffusion is the process that accomplishes the actual gas exchange across the
alveolar walls. This process requires normal alveolar septae (the walls of the
air sacs) that contain intact capillaries. Finally, a normal blood supply
depends on normal capillaries, normal red blood cells (no anemia), and normal
pumping of blood by the heart. Any disease that interferes with ventilation,
diffusion, or blood supply to the lung will impair lung (pulmonary) function and
decrease delivery of oxygen to the tissues of the body.
Next: What are the abnormalities (diseases) in smoker's lung? »
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