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Pulmonary Health: The Lungs, Smoking and COPD

April 18, 2012 | Comments: 0 | Views: 193

The lungs in mammals and other vertebrates likely evolved from the swim bladders of fish. The swim bladder, while not primarily providing a respiratory function, is physiologically similar to lungs. That is, swim bladders in primitive fish connect to the digestive system, and can be filled by gulping in air. In other fish, gas exchanges between the swim bladder and the blood stream, eliminating the need for the fish to gulp in air at the surface. By combining these two functions, the swim bladder would essentially be a lung. Furthermore, while there are a few organisms with both gills and lungs (such as the lungfish), there are none with both lungs and a swim bladder, which would be expected if lungs evolved from swim bladders.

The lungs of mammals and birds are highly optimized for gas exchange. Warm-blooded vertebrates have high requirements for oxygen, since the base metabolic rate is so high when compared to cold-blooded creatures. Birds in particular have astronomically high needs for oxygen.

In mammals, the bronchi (tubes that carry air between the lungs and outside world) are a two-way street. That is, the air flows in and out though the same passages. This is called tidal respiration, since the air moves like ocean tides. This is not a completely efficient system, since the inhaled and exhaled breaths are not 100% oxygen and carbon dioxide, respectively.

Birds accomplish respiration more efficiently, since they have much higher demands for oxygen, and must keep a low weight. Instead of tidal respiration, bird lungs are comprised of tubes open on two ends, allowing for a continuous, one-direction flow of air. This means that oxygenated air never mixes with carbon dioxide rich air, enabling greater respiratory efficiency.

To make up for the lack of relative efficiency (mixing inhaled and exhaled air), human lungs have an enormous surface area. The inside of a lung is folded and convoluted such that if it were completely flattened out, the area would equal that of a tennis court. On the surface of a lung, the blood vessel walls are only about one cell thick. Oxygen and carbon dioxide are able to pass through them easily, from the air passages into the bloodstream.

Health professionals often warn against the dangers of smoking. Smoking generally impacts the efficiency of the lungs to transfer air between the outside world and the blood. This happens in several ways.

One way that smoking diminishes the efficiency of the lungs is by coating them with tar. This is true of any smoke, and does not have to be from tobacco. The tar simply serves as an additional barrier that oxygen and carbon dioxide must breach in order to pass into and out of the bloodstream. But tar, while the most visually disturbing effect, is not the most sinister or damaging.

Breakdown of the alveoli is more serious. The lung depends on its many folds to maximize surface area. Imagine a sponge: the smaller the holes, the more water it can hold. A sponge that has large holes like Swiss cheese will hold far less than one that does not. In the same way, as smoking destroys alveoli tissue, the area for oxygen transfer diminishes. At first this is not a problem, as the lungs have more than enough capacity to supply keep the body oxygenated when at rest. However, eventually major exertion becomes impossible, and then minor effort, such as climbing stairs becomes hard. Finally, even a resting state can leave a smoker breathless.

In addition to losing surface area the lungs also tend to harden and the passages become more narrow, allowing for less airflow. This condition is known among the medical community as chronic obstructive pulmonary disease or COPD. While COPD is a common effect of smoking or living in a highly polluted environment, it can also sometimes occur in non-smokers. Currently, COPD clinical research has not determined a clear cause of the condition in non-smokers.

Some COPD clinical testing has implicated genetics as a cause. Non-smoking family of regular smokers are probably more likely to have COPD than a non-smoking control. However, the proximity of regular smokers and second-hand smoke must also be considered.

For more information about the lungs, the human body, or COPD clinical research, see CONECTR is a clinical research organization dedicated to solving the health-related issues of the 21st century.

Source: EzineArticles
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