The lungs hare the vital organs of the respiratory system in
humans. They contain a network of tubes that range from the largest, the
trachea, to the bronchi that branch into each lung, to smaller bronchioles, and
then to the tiny sacs at the end of the branched bronchioles called alveoli.
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| <http://www.breathmatters.org/what-is-copd-lung-disease.php> |
Alveolar Structure
The alveoli are very small, spherical sacs grouped into clusters at the end of bronchioles. They have very thin walls and are surrounded by lattices of capillaries. These are the most important parts of the lungs because this is where the transport of O2 between the lungs and the bloodstream happens as the O2 diffuses from the area of high concentration (alveoli) to low concentration (bloodstream).
The average human adult has around 500 million alveoli, (1) and the area created by these is the equivalent to two tennis courts. (2)
The alveoli are very small, spherical sacs grouped into clusters at the end of bronchioles. They have very thin walls and are surrounded by lattices of capillaries. These are the most important parts of the lungs because this is where the transport of O2 between the lungs and the bloodstream happens as the O2 diffuses from the area of high concentration (alveoli) to low concentration (bloodstream).
The average human adult has around 500 million alveoli, (1) and the area created by these is the equivalent to two tennis courts. (2)
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| <http://ibbio.pbworks.com/w/page/40290209/Gas%20exchange> |
Surface Area in the Respiratory System
The human body is large and complex, containing
approximately 3.72 × 1013 cells. (3) Every
cell requires O2 to carry out its respiration function that provides
the energy that is vital to the health of not only the cell, but the entire
organism. Given that O2 is so vital, and the number of cells in the
human body is so vast, a large volume of oxygen must enter the body constantly.
We also haven’t yet mentioned the large volume of CO2, one of the
products of respiration, which must also be removed from the body constantly.
The average healthy adult human has a maximum lung capacity
of around 6 litres (4) and each resting inhalation is usually around
500ml. (5) The resting breathing rate of a healthy adult is 15–20 breaths
per minute – a breath every 3–4 seconds (let’s average it to 3.5 seconds). (6)
Air is, on average, 21% O2. That means that the
volume of O2 inhaled in a standard resting breath is: 0.21 x 500ml =
105ml.
As one mole of any gas occupies 25.4L at SLC, 0.105L is 0.004
moles. This number of moles, multiplied by 6.02 x 1023 (Avogadro’s
number) gives us the number of O2 molecules in a standard resting
breath: 2.408 x 1021.
2.408 x 1021 is an astoundingly large number.
Every 3.5 seconds, 2.408 x 1021 O2 molecules pass through
the alveoli of the human lung into the blood stream. If the rate of oxygen
transport through the alveolar walls and into the surrounding capillaries isn’t
sufficient to meet the needs of the body’s cells, those cells will quickly
perish and so will the body. It takes only a few minutes of continued O2
deprivation to permanently damage brain cell function and/or cause death. (7)
It is for this reason that the surface area of the alveoli is so vital –
without a very high rate of O2 transport, the body will very quickly
die.
What Happens when Alveolar Surface Area is Reduced?
There are many lung diseases that reduce the available
alveolar surface area. These include emphysema, pneumonia and lung cancer.
Emphysema
The alveoli of emphysema sufferers are damaged. This often arises through the inhalation of impure air containing smoke or pollutants like asbestos. The walls of individual alveoli are destroyed, turning the groups of individual spherical alveoli into large, single sacs. The loss of the individual alveolar walls is a detrimental loss of surface area, reducing the capacity of sufferers to transport respiratory gases efficiently. Emphysema sufferers are also much more likely to develop lung cancers and pneumonia. (8)
The alveoli of emphysema sufferers are damaged. This often arises through the inhalation of impure air containing smoke or pollutants like asbestos. The walls of individual alveoli are destroyed, turning the groups of individual spherical alveoli into large, single sacs. The loss of the individual alveolar walls is a detrimental loss of surface area, reducing the capacity of sufferers to transport respiratory gases efficiently. Emphysema sufferers are also much more likely to develop lung cancers and pneumonia. (8)
Pneumonia
Pneumonia is a respiratory infection where the alveoli of the lungs become coated with mucous and/or inflamed, significantly reducing the alveolar surface area available for O2 transport. Sufferers of pneumonia often have a higher breath rate than those without pneumonia to try make up for the lost surface area caused by the infection. They also cough to attempt to remove the mucous and suffer symptoms associated with oxygen deficiency that include headache, fatigue and confusion. (9)
Pneumonia is a respiratory infection where the alveoli of the lungs become coated with mucous and/or inflamed, significantly reducing the alveolar surface area available for O2 transport. Sufferers of pneumonia often have a higher breath rate than those without pneumonia to try make up for the lost surface area caused by the infection. They also cough to attempt to remove the mucous and suffer symptoms associated with oxygen deficiency that include headache, fatigue and confusion. (9)
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| http://en.wikipedia.org/wiki/Pneumonia |
Lung Cancer
Cancers often arise in the epithelial (lining) cells of the body, including in the alveolar sacs. The cancerous cells will spread quickly and reduce the surface area of healthy alveoli, making it difficult for O2 transport to take place efficiently.
Cancers often arise in the epithelial (lining) cells of the body, including in the alveolar sacs. The cancerous cells will spread quickly and reduce the surface area of healthy alveoli, making it difficult for O2 transport to take place efficiently.
In Conclusion
The structure and function of the respiratory system are
intimately and inseparably related. If the alveoli of the lungs did not have
such a huge surface area, the human body would not be supplied with the large
amounts of oxygen it requires to function and survive.
