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The Lung

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Lung is the chief breathing organ of mammals, birds, reptiles, and most adult amphibians. The main job of the lungs is to exchange gases. As blood flows through the lungs, it picks up oxygen from the air and releases carbon dioxide. The body needs oxygen to burn food for energy, and it produces carbon dioxide as a waste product. This article discusses the human lungs, but the lungs of other animal's function in a similar way. Parts of the lungs. Human beings have two lungs--a left lung and a right lung--, which fill up most of the chest cavity. A lung has a spongy texture and may be thought of as an elastic bag filled with millions of tiny air chambers, or sacs. If the walls of the air sacs could be spread out flat, they would cover about half a tennis court. The somewhat bullet-shaped lungs are suspended within the ribcage. They extend from just above the first rib down to the diaphragm, a muscular sheet that separates the chest cavity from the abdomen. A thin, tough membrane called the visceral pleura covers the outer surface of the lungs. The heart, large blood vessels, and oesophagus (the tube connecting the mouth and stomach) lie between the two lungs. ...read more.


Gas exchange in the lungs. In order to supply oxygen to the blood and remove carbon dioxide from it, the lungs must draw in fresh air and expel stale air. Fresh air is drawn in when the diaphragm and the muscles between the ribs contract. This action--called inspiration or inhalation--makes the chest volume larger and causes the lungs to expand. The expansion creates a slight vacuum in the lungs, and air from the atmosphere flows in. When the muscles relax, the lungs return to a smaller volume, and gas flows out into the atmosphere. This action is called expiration or exhalation. Blood entering the lungs through the pulmonary circulation is dark-coloured, low in oxygen, and high in carbon dioxide. It is pumped by the right side of the heart into the pulmonary arteries, which lead to the lungs. The pulmonary arteries divide into smaller and smaller blood vessels, ending with pulmonary capillaries in the walls of the alveoli. The alveolar walls are so thin that oxygen and carbon dioxide move through them easily. Oxygen passes from the alveoli to the blood in the capillaries. At the same time, carbon dioxide leaves the blood and enters the alveoli. ...read more.


In other cases, the particles can resist or destroy the macrophages. Because lung diseases can result from many different causes, they are usually grouped by how they affect lung functions. Obstructive lung diseases, such as emphysema, asthma, and chronic bronchitis, cause the airways to become partly blocked or narrower, making it more difficult for air to move through them. Cigarette smoking and air pollution are major causes of these diseases. Restrictive lung diseases make it harder for the respiratory system to expand. They can cause a stiffening of the lung or chest wall or make the respiratory muscles unable to respond to nerve signals. Breathing in substances such as asbestos, silica, and coal dust can cause some types of restrictive disease. Pulmonary vascular diseases affect the circulation of blood in the lungs. For example, in pulmonary hypertension, the small blood vessels of the lung become narrower, making it difficult for the right side of the heart to pump blood. Some diseases are difficult to categorize because they can harm the lungs in a number of ways. Some pollutants--particularly cigarette smoke--affect the cilia, causing the upward movement of mucus to slow or stop. Smoking cigarettes is also a major cause of lung cancer. Infectious lung diseases, such as tuberculosis and pneumonia, are caused by bacteria, viruses, or other organisms. These diseases are major killers in developing countries. ...read more.

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