The lungs are the main organs of the respiratory system located in the lateral cavities of the chest. The lungs are separated from each other by the mediastinum. They are covered with the pleura. Each lung has the base, apex, two borders and three surfaces. The lung has the apex extending upward 3-4 centimetres (cm) above the level of the first rib. The base of the lungs is located in the convex surface of the diaphragm.
In the adults the weight of the lungs is about 1,350 g. The right lung consists of 3 lobes. It is about 15% heavier than the left one consisting only of two lobes. The vital capacity of the lungs is 3.5 litres.
The lungs take part in the production of physiologically active substances, in the regulation of blood coagulation and the metabolism.
The structure of the lung consists of an external serous coat, the visceral layer of the pleura, a subserous elastic tissue and the parenchyma or proper substance of the lungs.
In the process of respiration oxygen passes into the blood and carbon dioxide passes into the atmospheric air. The exchange of oxygen and carbon dioxide takes place in the alveoli of the lungs. It is due to the difference of partial pressure of these gases. Hemoglobin is that substance of the blood which transfers oxygen in the blood.
In the process of inspiration the volume of the chest increases and the lungs extend. The pressure in the lungs becomes less and the atmospheric air enters the lungs. In the process of expiration the volume of the chest decreases, and the lungs contract. The pressure in the lungs becomes higher and the air goes out of the lungs.
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