Lungs

The lungs (also spelled sanbab) are respiratory organs located in the chest. Humans and other mammals have two lungs, one on the right and one on the left, positioned in the cavity of the chest on either side of the heart. The primary function of the lungs is the exchange of gases: oxygen is extracted from inhaled air and enters the blood, while carbon dioxide is removed from the blood and exhaled.

The lungs themselves have no muscles to move. Respiration is performed by the diaphragm (the muscle that separates the chest from the abdomen) and the muscles between the ribs. When these muscles contract, the volume of the chest cavity decreases, and air flows into the lungs.

Structure

Air passes through the nose or mouth, then through the windpipe (trachea), which branches into two bronchi, one entering each lung. Each bronchus divides into smaller branches (bronchioles) until they end in tiny sacs called alveoli. It is in the alveoli that gas exchange actually occurs, because their walls are very thin and are surrounded by a network of tiny blood vessels (capillaries).

The right lung typically has three lobes, while the left has two, because the heart occupies space on the left side. Both lungs are covered by two thin membranes called the pleura, between which is a small amount of fluid that reduces friction during breathing.

Other Functions

The lungs do more than just exchange gases. They help regulate the acidity level (pH) of the blood by removing carbon dioxide. They also contribute to the body's defense: the lining of the bronchi produces mucus that traps dust and germs, and tiny hairs (cilia) push it upward for removal.

Diseases and Damage

Conditions affecting the lungs include pneumonia, tuberculosis, asthma, chronic obstructive pulmonary disease (COPD), and lung cancer. Smoking, air pollution, and occupational dust increase the risk of many of these. Diagnosis is usually made by chest X-ray, CT scan, and tests measuring breathing capacity.