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Anatomy of the Respiratory System


Lt Col Reynolds
The primary function of the respiratory system is to obtain oxygen for use by the body's cells, and to eliminate the carbon dioxide that the cells produce. Dr. Green, can you tell us how the respiratory system does this?

Dr. Green
Well, Dr. Reynolds, the first step in understanding the respiratory system is to take a look at the various parts. In general, this system includes airways that lead into and out of the lungs, and, of course, the lungs themselves.

The lungs allow oxygen to enter the body in exchange for its waste product, carbon dioxide. As the oxygen passes through the nose and mouth, it is rapidly warmed and moistened to avoid injury to the delicate lining of the airways.

The nose and airways trap large particles, like dust, pollen, molds, bacteria, and chemicals, which could cause serious harm to the lungs. The air is then transported through the trachea and bronchi to smaller airways called bronchioles. These airways have branches like a tree, so that millions of small airways can carry oxygen to tiny air sacs called alveoli.

The airways have a delicate cellular lining called mucosa, which is coated with a thin layer of mucus. Foreign particles are trapped by the sticky mucus and removed from the airways through a cleansing process. Tiny hair-like structures, called cilia, move the mucus and trapped foreign particles up toward the mouth and nose where they are coughed out, sneezed out, or swallowed.

Bundles of muscles surround the airways, and the contraction of these muscles directs the flow of air.

The body needs a continuous supply of oxygen for cellular respiration, and at the same time, it must get rid of excess carbon dioxide, which is the poisonous waste product created in the body’s cells. Gas exchange is the exchange of oxygen and carbon dioxide between the air and the blood in the lungs.

Blood enters the lungs through the pulmonary arteries. It then moves through arterioles and into the alveolar capillaries. Oxygen and carbon dioxide are exchanged between blood and the air. The newly oxygenated blood then flows back to the heart through the pulmonary veins, so the heart can distribute oxygen to the rest of the body.