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We can go without water for days and do without food even longer, but without air we will die in a matter of minutes. Breathing, along with the beating of our hearts, is one of the body's most essential functions, and any disruption can be deadly. Even a minor cold, by affecting our normal intake and outflow of air, can make us feel miserable.
Respiratory problems are common--indeed the most common of all physical complaints. Almost everyone experiences infections of the head, throat, and chest. These infections range from colds to influenza and pneumonia, which can be mildly debilitating or seriously life-threatening.
How the Respiratory System Works
The nose, lungs, and diaphragm are the major respiratory organs. As the diaphragm contracts, the rib cage expands. This action creates negative pressure in the lung cavity, and air is then pulled in through the nose. When the diaphragm stops contracting, the lungs recoil and push the air out. Oxygen is exchanged for carbon dioxide (C[O.sub.2]) in the blood that flows through the capillaries in any one of the lung's 300 million alveoli. Circulating blood then delivers the oxygen to the body's cells in exchange for C[O.sub.2] and metabolic waste. This trade is known as internal respiration. The lungs subsequently exhale C[O.sub.2]-containing air.
Colds and Flu
The common cold is aptly named: It ranks as the most prevalent infectious disease in humans. Indeed, the common cold accounts for just about as many trips to the drugstore as any other ailment. And although the common cold tends to be benign and brief, this nuisance illness can lead to more serious bacterial infections.
Colds are almost always caused by viral infections of the upper respiratory tract. Many different families of viruses can cause a common cold, and each family has numerous members. The sheer diversity of causative agents is why it has been impossible to develop a vaccine for the common cold.
Different viruses affect different areas of the respiratory tract and may result …